Catenated phosphorus materials, their preparation and use, and semiconductor and other devices employing them

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and where x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconductors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Rectifying Schottky junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti as junction forming top contacts. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus. The materials may be employed as protective coatings, optical coatings, fire retardants, fillers and reinforcing fillers for plastics and glasses, antireflection coatings for infrared optics, infrared transmitting windows, and optical rotators.

TECHNICAL FIELD 
This invention relates to catenated phosphorus materials, their preparation 
and use, and to semiconductor and other devices employing them. These 
materials include high phosphorus polyphosphides (i.e., phosphides where 
the polymeric nature is maintained), alkali metal polyphosphides, 
monoclinic phosphorus and new forms of phosphorus. Vapor transport is 
employed in making the crystalline, polycrystalline and amorphous 
phosphorus and polyphosphide materials in bulk, thick and thin films. 
Flash evaporation and chemical vapor deposition are used to make thin 
films. A condensed phase technique is utilized in producing crystalline 
and polycrystalline polyphosphides. Diffusion doping is employed to raise 
the conductivity of these materials. Rectifying junctions are formed with 
the materials by appropriate metal contacts. The film materials may be 
used as optical coatings. Powdered crystals and amorphous materials may be 
used as fire retardant fillers. The crystalline materials, especially the 
fibrous forms, may be employed as the high tensile components of 
reinforced plastics. 
BACKGROUND ART 
During the past several decades, the use of semiconductors has become ever 
increasingly widespread and important. Silicon based semiconductors, for 
example, have generally been successful in providing a variety of useful 
devices, such as p-n junction rectifiers (diodes), transistors, silicon 
control rectifiers (SCR's), photovoltaic cells, light sensitive diodes, 
and the like. However, due to the high cost of producing crystalline 
silicon and the ever-increasing demand for semiconductors over a 
broadening range of applications, there has been a need to widen 
correspondingly the scope of available useful semiconductor materials. 
Useful semiconductors of the present invention, have an energy band gap in 
the range of about 1 to 3 eV (more specifically 1.4 to 2.2 eV); a 
photoconductive ratio greater than 5, (more specifically between 100 and 
10,000); a conductivity between about 10.sup.-5 and 10.sup.-12 
(ohm-cm).sup.-1 (more specifically conductivity in the range of 10.sup.-8 
to 10.sup.-9 (ohm-cm).sup.-1); and chemical and physical stability under 
ambient operating conditions. Accordingly, while many materials may be 
semiconducting in the sense they are not pure metals or pure insulators, 
only these semiconducting materials which meet these criteria may be 
considered to be useful semiconductors in the context of this invention. 
Given the present need to develop alternative nonpetroleum based energy 
sources, the potential commercial utility of a semiconductor increases 
dramatically when the semiconductor also exhibits an effective 
photovoltaic characteristic, that is, the ability to economically and 
efficiently convert solar energy into electrical potential. 
From an economic standpoint, amorphous semiconductors, particularly in the 
form of thin films, are more desirable than single crystalline forms due 
to potential lower cost of production. Amorphous semiconductors also have 
better electrical qualities than polycrystalline forms of the same 
material as used in many semiconductor devices. 
The semiconductor industry has continued its search for useful new 
semiconductor materials beyond crystalline silicon, and the like. 
In the non-silicon crystalline area, single crystals of semiconducting 
compounds, including GaAs, GaP, and InP, are in commercial use. 
Many other semiconductor materials have been utilized for specialized 
purposes. For example, CdS and selenium are utilized as the photoconductor 
in many xerographic machines. 
In this application semiconductor device means a device including a 
semiconductor material whether the device employs electrical contacts, 
that is, is an electronic device, or whether it is a non-electronic 
device, such as the photoconductors employed in xerography, phosphorescent 
materials, the phosphorus in a cathode ray tube, or the like. 
Although some of the known forms of phosphorus have been stated to have 
semiconducting properties, many are unstable, highly oxidizable and 
reactive, and no known form of phosphorus has been successfully employed 
as a useful semiconductor. 
The group 3-5 materials such as gallium phosphide and indium phosphide are 
tetrahedrally bonded and thus, as will be pointed out below, are clearly 
distinguished from the compounds disclosed herein. Furthermore, their 
semiconducting properties are not dominated by phosphorus-to-phosphorus 
bonding, i.e. the primary conduction paths are not the 
phosphorus-to-phosphorus bonds. 
Others have disclosed hydrogenated phosphorus having a structure similar to 
black phosphorus and having semiconducting properties. 
Considerable work on high phosphorus polyphosphides has been done by a 
group headed by H. G. von Schnering. The various reports from this group 
indicate that the highest phosphorus containing polyphosphide compound 
they have produced is crystalline MP.sub.15 (M=group 1a metal). These 
polyphosphides are produced by heating a mixture of metal and phosphorus 
in a sealed ampule. Von Schnering reports that based on their structure 
polyphosphides are classified as valence compounds in a classical sense, 
and that this means that these compounds are, or should be, insulators or 
semiconductors, i.e. not metals. 
Monoclinic phosphorus, also called "Hittorf's phosphorus, is prepared 
according to the prior art from white phosphorus and lead as follows: 1 g 
of white phosphorus and 30 g of lead are heated slowly to a melt in a 
sealed tube to 630.degree. C. and held for a short time at that 
temperature. The solution is then cooled at the rate of 10.degree. per day 
for 11 days to 520.degree. C., and cooled rapidly to room temperature 
thereafter. It is next electrolyzed in a solution of 2 kg of lead acetate 
in 8 liters of 6% acetic acid, and the phosphorus is collected in a watch 
glass placed under the anode. Nearly square tabular crystals, about 
0.2.times.0.2.times.0.05 mm, are obtained in this way. 
The structure of this prior art monoclinic phosphorus has been determined 
by Thurn and Krebs. The crystals comprise two layers of pentagonal tubes 
of phosphorus with all of the tubes parallel, and then another pair of 
layers of all pentagonal tube phosphorus, the tubes in the second pair of 
layers all being parallel, but the tubes in the second pair of layers 
being perpendicular to the tubes in the first pair of layers. The space 
group of the crystals has been determined, as well as the bond angles and 
bond distances. See the summary of the prior art in the section 
"Phosphorus" from "The Structure of the Elements" by Jerry Donahue, 
published in 1974. 
The electronic properties of Hittorf's phosphorus crystals have not been 
reported. Because of their small size the electrical properties cannot be 
readily determined. 
The preparation of high purity electronic grade phosphorus according to the 
prior art is very complex and time consuming, thus electronic grade 
phosphorus is very expensive. 
The prior art also exhibits a need for stable phosphorus compounds for use 
as fire retardants. Crystalline forms have additional utility as 
reinforcing additives in plastics, glasses and other materials. 
DISCLOSURE OF THE INVENTION 
We have discovered a family of alkali metal phosphosphide materials 
possessing useful semiconductor, optical, and mechanical properties. 
USEFUL SEMICONDUCTOR PROPERTIES 
By "polyphosphide" we mean a material dominated by multiple 
phosphorus-to-phosphorus bonds. By "useful semiconductor" we mean not only 
that the conductivity is intermediate between insulators and metals, but 
also the demonstration of a host of useful properties: 
Stability 
Resilient material structure 
Bandgap in a useful range (typically 1 to 2.5 eV) 
High inherent resistivity, but with ability to be doped 
Good photoconductivity 
Efficient luminescence 
Ability to form a rectifying junction 
Ability to be formed at relatively low temperatures (for semiconductors) by 
processes amenable to scale-up 
Ability to be formed as large area amorphous thin films 
Ability to be formed as ductile polymeric fibers 
The polyphosphides are a unique family of materials possessing all of these 
features. 
PRESERVATION OF UTILITY IN MULTIPLE FORMS 
It is equally significant that the useful properties remain essentially 
constant over a wide range of chemical compositions and physical forms 
(crystalline and amorphous). 
To our knowledge, polyphosphides are the only useful semiconductors in 
which desirable single crystal-like properties are preserved in the 
amorphous form. This is of major technological significance because the 
amorphous form is at the least more amendable, and often essential, for 
large scale applications, such as photovoltaic cells, large area displays, 
and electrostatic copiers. 
But up to now, the problem with amorphous semiconductors is that they do 
not form readily as a stable single phase material. And even when they are 
forced to, the amorphous form loses some very desirable features of its 
crystalline counterpart. 
The dominant known semiconductor (silicon) has a tetrahedral coordination 
in its crystalline form. Any attempt to make it amorphous (to make 
amorphous Si) is known to be accompanied by a breaking of the tetrahedral 
bonds, leaving "dangling bonds" that destroy useful semiconducting 
properties. Pure amorphous Si is useless: unstable and crumbly. Attempts 
to satisfy the dangling bonds with Hydrogen or Fluorine have been only 
partially successful. 
CENTRAL ROLE OF STRUCTURE 
We believe that the preservation of useful properties among the multiple 
forms of the polyphosphides are a direct result of the structure of the 
materials which, in turn, is made possible by the unique properties of 
phosphorus, particularly its ability to form polymers dominated by 3 
phosphorus to phosphorus covalent bonds at the vast majority of phosphorus 
sites. 
In the crystalline form, the polyphosphides of the type MP.sub.15 (with 
M=Li, Na, K, Rb, Cs) have a structure formed by a phosphorus skeleton 
consisting of parallel tubes with pentagonal cross section. These 
phosphorus tubes are linked by P-M-P bridges shown in FIGS. 4, 5 and 6. 
The building block for this MP.sub.15 atomic framework can be viewed as 
P.sub.8 (formed by 2 P.sub.4 rigid units) and MP.sub.7 (formed by the 
association of MP.sub.3 and P.sub.4 rigid units). 
Using the building blocks or clusters described above, Kosyakov in a review 
article (Russian Chemical Review, 48(2), 1979) showed theoretically that 
these polyphosphide compounds could be treated as polymeric materials 
using their basic building blocks as monomers. Hence, in principle it is 
possible to construct a large number of atomic frameworks having the same 
phosphorus skeletons. 
In our work, we have synthesized by various techniques described later, 
MP.sub.15 crystals and also compositions of the type [MP.sub.7 ].sub.a 
[P.sub.8 ].sub.b with b much greater than a. These novel phosphorus rich 
compounds originally observed as 37 fibers", "whiskers", or "ribbons" are 
referred to in this investigation as MP.sub.x with x much greater than 15. 
These low metal content materials are prepared by vapor transport as thick 
films (greater than 10 microns) of polycrystalline fibers and large boules 
(greater than 1 cm.sup.3) of amorphous character. The polycrystalline 
fibers exhibit the same morphology as KP.sub.15 whiskers. 
The structural framework of the first MP.sub.x (x much greater than 15) 
crystalline materials we discovered is dominated by a phosphorus skeleton 
similar to the phosphorus framework of the MP.sub.15 compounds. 
We have found that the useful electrical and optical properties of these 
crystalline materials MP.sub.15 and MP.sub.x (x much greater than 15) are 
similar. The properties of these materials are therefore dominated by the 
multiple P-P covalent bonds of the phosphorus skeletons with a 
coordination number somewhat less than 3. To our surprise we have also 
discovered that the useful electro-optical properties of these materials 
were essentially preserved for MP.sub.15 and MP.sub.x (x much greater than 
15) crystalline materials and their amorphous counterparts. 
Unlike previously known materials, this is a one dimension rigid structure 
and is resilient in the following sense. The polyphosphide crystal 
symmetry is very low (triclinic). We believe that in the transition from 
the crystal to the amorphous form, the low symmetry material is capable of 
accommodating in a gradual way the increased structural disorder that 
characterizes the amorphous state. There is no ripping apart of strong 
tetrahedral bonds (coordination number of 4) as in silicon because the 
phosphorus, with a much lower coordination number than silicon, can accept 
much greater structural disorder without the creation of dangling bonds. 
The polyphosphides are polymeric in nature. The result is a polymeric 
amorphous structure with no apparent X-ray diffraction peaks, one with 
longer-range local order than is achievable with conventional amorphous 
semiconductors. We believe that this gradual onset, in the structural 
sense, of amorphicity is the reason for the preservation of the desirable 
crystal properties in the amorphous polyphosphides. 
DISTINGUISHABLE FROM KNOWN, USEFUL SEMICONDUCTORS 
The composition and structure of the family of polyphosphides clearly 
distinguishes them from all known, useful semiconductors: 
______________________________________ 
Group 4a (Crystal Si, amorphous Si:H, etc.) 
3a-5a (III-V) (GaAs, Gap, Inp, etc.) 
2b-6a (II-VI) (CdS, CdTe, HgCdTe, etc.) 
Chalcogenides (As.sub.2 Se.sub.3) 
1b-3a-6a (CuInSe.sub.2) 
______________________________________ 
DISTINGUISHABLE FROM KNOWN FORMS OF PHOSPHORUS 
The alkali polyphosphides (MP.sub.x, M=Li, Na, K, Rb, Cs; where x=15 and 
much greater than 15) are phosphorus rich. In cases of "high x" material 
they are almost all phosphorus. Nonetheless, their structure (parallel 
pentagonal tubes) and their properties (stability, bandgap, conductivity, 
photoconductivity) clearly distinguish them from all known phosphorus 
materials (black, white/yellow, red, and violet/Hittorf). The structural 
relationships among these various forms are discussed below. 
Our work has done much to clarify this aspect of phosphorus itself. The 
nomenclature in this area has been somewhat confusing. The following 
summarizes our current usage. 
1. Amorphous P or Red P 
Amorphous red phosphorus is a generic term for all non-crystalline forms of 
red phosphorus, usually prepared by thermal treatment of white phosphorus. 
2. Violet P 
This microcrystalline form of red phosphorus is prepared from charges of 
pure P, either white or amorphous red, by extended thermal treatment. 
3. Hittorf's P 
Crystalline form of red phosphorus structurally identical to Violet P. 
Hittorf's P is prepared in the presence of a large excess of lead. Despite 
this, the terms "Hittorf's P" and "Violet P" have often been used 
interchangeably. The crystal structure consists of double layers of 
parallel pentagonal tubes, with adjacent double layers perpendicular to 
each other in a monoclinic cell. Hittorf's P crystals are somewhat larger 
(approximately 100 microns) than violet P microcrystals. 
4. Large Crystal Monoclinic Phosphorus 
Even larger crystals (several mm), essentially isostructural with the above 
two, are described herein. These novel crystals are prepared by Vapor 
Transport (VT) treatments of alkali-phosphorus charges. The inclusion of 
the alkali is apparently essential for formation of the large crystals. 
Analysis confirms the presence of alkali (500 to 2000 ppm) in these large 
crystals of phosphorus. 
5. Twisted Fiber Phosphorus 
A crystalline form of phosphorus described herein prepared by VT treatments 
of amorphous P charges. Believed to be nearly-isostructural with 
polycrystalline MP.sub.x "ribbons". 
ROLE OF THE METAL: WHY PHOSPHORUS IS NOT GOOD ENOUGH 
The many allotropic forms of elemental P are evidence for the variety and 
complexity of the bonds and structures that are accessible with 
phosphorus. We lack a detailed, comprehensive model of exactly how the 
alkali metal works, but have developed a large body of data showing that 
the metal stabilizes phosphorus so that a single unique structure may be 
selected from the ensemble of potentially available structures. 
Without at least some alkali metal, the following undesired phenomena 
occur: 
A. The phosphorus is unstable (e.g., White P). 
B. To the extent that a known single phase is accessible to the P, it can 
only do so at high temperatures and of a size limited to microcrystals 
(e.g., Violet P), or 
C. At high pressures (e.g., black P). 
D. Without an alkali metal in the charge, the MP.sub.x type of structure is 
not formed by vapor transport. Rather, the twisted phosphorus fiber form 
we have discovered is obtained. This crystalline phase is metastable and 
the structure is not well defined as shown by our X-ray, Raman and 
photoluminescence data. 
The presence of alkali metal in vapor transport favors the all-parallel 
untwisted phase. It also, as discovered by us, favors large crystals of 
monoclinic P to form at a different temperature. 
The dominant role of structure, not composition, as the determinant of 
properties is made clear by noting that KP.sub.x (x much greater than 15) 
has properties (bandgap, photoluminescence, Raman spectra) that are 
essentially those of KP.sub.15, but are somewhat different from those of 
monoclinic P. 
It is clear that even a little alkali metal can serve to select a stable 
phase. But will non-alkalis work? Krebs reported non-alkali 
polyphosphides, with tubular structures consisting of 2b-4a-P.sub.14 
(2b=Zn, Cd, Hg and 4a=Sn, Pb). Why do these form? 
A speculative hypothesis is that these materials form in the tubular 
structure because the Group 4a element is amphoteric and can occupy a P 
site in lieu of P. 
One can compute an effective electron affinity of the P.sub.15 framework 
based on the ionization energies of the alkali metals, all of which are 
less than or equal to 5.1 eV. One can, in turn, calculate effective 
ionization potentials for other possible compositions such as the 
2b-4a-P.sub.14 compounds. All of Krebs' materials noted above have 
"effective ionization" less than or equal to 4.8 eV. 
USEFUL PROPERTIES 
Our major initial discovery was that the KP.sub.15 whiskers (single 
crystal) were stable semiconductors, with an energy bandgap corresponding 
to red light (1.8 eV) and exhibiting efficient photoconductivity and 
photoluminescence. These are the hallmarks of a semiconductor with 
potential applications in electronics and optics. Whiskers of the other 
alkali MP.sub.15 materials also have these properties (M=Li, Na, Rb, Cs). 
To realize their potential, the materials had to be prepared in a size and 
form suitable for fabricating devices and for testing. We recognized that 
the crystal habit, however, is not conducive to growth of large, single 
crystals that are free of crystallographic "twinning". Large, twin-free 
single crystals are the basis of nearly all semiconductor device 
technology today. Polycrystalline materials are less desirable because 
even if the individual grains are large, the presence of grain boundaries 
serves to destroy some desirable properties due to the physical and 
chemical discontinuities that are associated with such boundaries. Hence, 
our attention turned to the amorphous forms we had discovered. 
Useful amorphous semiconductors, whether used as a junction device such as 
a photovoltaic cell, or as a coating such as in an electrostatic copier, 
have been generally made as thin films for extrinsic reasons (cost, 
manufacturing ease, and application need) and intrinsic reasons (material 
problems in the bulk amorphous state). 
We have discovered that KP.sub.15 can be made as a stable amorphous thin 
film (by Vapor Transport). (This cannot be done with silicon: amorphous Si 
is not stable, while single crystal Si is.) 
Stable, bulk, and thin film amorphous KP.sub.x (x much greater than 15) can 
also be made by vapor transport. 
There is evidence that these polyphosphides are unusual in yet another way. 
The useful properties of these materials MP.sub.15 and MP.sub.x (x much 
greater than 15) are similar in their crystalline forms and their 
amorphous counterparts as shown in Tables XVI and XVII below. 
Applications utilizing amorphous thin film KP.sub.15 requiring no junctions 
can be readily envisioned (e.g., electrostatic copying). In fact, the high 
inherent resistivity (approximately 10.sup.8 to 10.sup.9 ohm-cm) is an 
advantage for such junctionless system applications. 
Electronic and opto-electronic devices all require that some junction be 
formed in or with the material. This requires lowering the resistivity of 
the material by doping. 
We have discovered that Ni diffused into KP.sub.15 serves the purpose of 
reducing the resistivity of the material by several orders of magnitude. 
Surface analysis has demonstrated that Ni diffusion from the solid state 
(KP.sub.15 deposited onto a layer of Ni) follows a normal diffusion 
pattern during the growth process of the film. 
Device configurations with Ni as a back contact and diffuser; and other 
metals, such as Cu, Al, Mg, Ni, Au, Ag and Ti as top contacts, lead to 
junction formation. Junction Current-Voltage (I-V) characteristics have 
been measured with these top contacts. Junction Capacitance-Voltage (CV) 
characteristics have been measured with Al and Au top contacts. The data 
indicates double junction formation with a high resistance layer near the 
top contact. 
The high resistance layer is an undoped portion of the KP.sub.15 film which 
results from the present doping procedure. 
A small photovoltaic effect (micro amp current under a short circuit 
condition) has been observed. 
SYNTHESIS OF POLYPHOSPHIDES 
Below are described the methods we have discovered that will produce 
polyphosphides of varying composition and morphology. 
A. Condensed Phase (CP) Synthesis 
This refers to the process of isothermal heat-up, soak (heating at set 
temperature), and cool down of starting charge carried out in a container 
of minimum volume. There is no vapor transport. Crystalline and bulk 
polycrystalline MP.sub.15 are produced. 
B. Single Source Vapor Transport Synthesis (1S-VT) 
A starting reactant charge is located in one area of an evacuated tube 
which is heated to a temperature, Tc, which is greater than Td, where Td 
represents the temperature(s) of other area(s) of the tube where materials 
deposit from the vapor. Crystalline MP.sub.15 ; crystalline, 
polycrystalline (bulk, and thin films) and amorphous bulk high x, MP.sub.x 
; monoclinic phosphorus; star shaped fiber; and twisted fiber phosphorus 
are produced. 
C. Two Source Vapor Transport Synthesis (2S-VT) 
Source reactant charges loaded in an evacuated chamber are separated 
physically by distance with a deposition zone between them. The two 
sources are heated to temperatures greater than the deposition zone (in 
order to get amorphous material, at least; see below). The deposition zone 
need not be the coldest one in the system, but a colder area should not be 
able to trap more than one component. 2S-VT was the first method used to 
make thin film amorphous KP.sub.15. Polycrystalline and amorphous thin 
films of MP.sub.15 and polycrystalline thin films and bulk amorphous high 
x, MP.sub.x are produced. 
D. Melt Quench 
A charge is heated in a sealed evacuated tube (isothermally, if possible) 
to temperatures greater than the "melting point" as determined by 
endotherms observed in DTA experiments, and held there for some period of 
time. The tube is then removed from the furnace and rapidly cooled. 
CsP.sub.7 glass has been produced. 
E. Flash Evaporation 
A charge in powder form is fed in small amounts, under a slight Argon flow, 
into an RF-heated susceptor, which is maintained at temperatures greater 
than about 800.degree. C. Inside the susceptor, the material is put 
through a tortuous path where it is, in theory, forced to contact hot 
surfaces. This is intended to rapidly and completely vaporize the charge 
such that the composition of the resultant vapor stream is the same as 
that of powder being injected. The vapor stream is directed into an 
evacuated chamber where it strikes cooler surfaces, resulting in 
condensed-product materials. Amorphous films have been produced. 
F. Chemical Vapor Deposition (CVD) 
In general, this refers to production of material by mixing two (or more) 
vaporized components which must undergo some chemical reaction to give 
products. As practiced by us, K and P.sub.4 are independently metered into 
furnaces where they are rapidly vaporized and carried downstream by the 
Argon flow to a cooler reaction chamber where the combined streams yield 
condensed product materials. 
The significance of CVD lies in that of these methods, it is the most 
amenable to scale-up and to doping in situ, i.e., simultaneous synthesis 
and doping of material. Amorphous thin films of KP.sub.15 have been 
produced. 
G. Molecular Flow Deposition (MFD) 
This is a multi-source vapor transport technique that draws on 2S-VT and 
Molecular Beam Epitaxy (MBE). Independently heated sources are used and 
the vaporized species are allowed to reach the substrate (also 
independently heated) at a controlled rate not achievable with 2S-VT. The 
deposition takes place in an evacuated chamber with in situ monitoring of 
the deposition (also not available with 2S-VT). The chamber may be sealed 
or continuously evacuated to control pressure. 
KP.sub.15 Materials 
A large variety of polyphosphide materials of different physical forms and 
compositions were initially prepared during our investigations. 
However, for potential useful semiconductor applications, the emphasis of 
our work has changed from the preparation of single crystal materials to 
that of amorphous materials--either in bulk or large area thin films. 
Among all the MP.sub.15 materials KP.sub.15 is a unique crystalline higher 
polyphosphide (x the same as or greater than 7) compound which exists for 
the K-P system. (In contrast, the other alkali metals can form compounds 
with x=7 or x=11, such as CsP.sub.7, NaP.sub.7, RbP.sub.11, etc.). 
KP.sub.11 and KP.sub.7 do not form as compounds. For this reason, the K-P 
system is easier to control than the other alkali-metal-P systems, where 
multiple compounds can form. 
In addition, from the results of our experimental work, it is apparent that 
whenever K+P are vaporized, by whatever means, and brought in the proper 
ratio ([P]/[K] the same as or greater than 15) to a zone whose temperature 
is in the proper window, amorphous KP.sub.15 will form. By this window we 
mean the temperature must be low enough to prevent crystallization of 
KP.sub.15 and high enough that KP.sub.x, where x is much greater than 15, 
is not deposited. 
Based on this tenet, all synthesis methods can be seen to operate on the 
same general principle. Each method simply used different means to achieve 
control of source vaporization or control of deposition. The two source 
systems (2S-VT, CVD and MFD) are particularly useful as the important 
variables can be independently controlled. 
Based on the above considerations, KP.sub.15 amorphous in thin films has 
been selected by us as our leading composition for the development of 
useful semiconductor materials. 
SUMMARY 
In a general inquiry into the nature of polyphosphides, potassium 
polyphosphide whiskers of about 1 cm in length were produced by single 
source vapor transport. In investigating the properties of this material 
it was determined by x-ray diffraction of a single crystal that the 
crystals were KP.sub.15. It was also discovered that these crystals were 
semiconductors. When measuring an emission at 4.degree. K. under argon 
laser illumination, photoluminescence was observed having an energy of 1.8 
eV, thus indicating that the material possibly had a band gap within this 
energy range. 
Later, in order to determine the conductivity of these whiskers, leads were 
attached with silver paint. In order to see if the leads were actually 
attached to a very small crystal, it was placed under a microscope while 
the conductivity was measured. Surprisingly the conductivity changed 
dramatically when the crystal was moved in the microscope, changing the 
illumination. A photoconductivity ratio of 100 was measured with the 
unilluminated conductivity of the whisker being about 10.sup.-8 
(ohm-cm).sup.-1. To establish whether the whiskers had a band gap, 
measurements were then made of the wavelength dependence of the 
photoconductivity, the wavelength dependence of the optical absorption and 
the temperature dependence of the conductivity of the whisker. These 
measurements, together with the photoluminescence measurement at 4.degree. 
K., established that the whiskers had a band gap of approximately 1.8 eV. 
Thus it was established that KP.sub.15 crystalline whiskers were 
potentially useful semiconductors. 
An amorphous film was formed on the inside of the quartz tube during the 
vapor transport production of the KP.sub.15 whiskers. This amorphous film 
was also found to have a band gap on the order of 1.8 eV and a 
photoconductivity ratio on the order of about 100. Like the whiskers, the 
amorphous film had an electrical conductivity of approximately 10.sup.-8 
(ohm-cm).sup.-1. Thus it was established that it also was a potentially 
useful semiconductor. 
The problem then presented to the inventors was whether KP.sub.15 could be 
produced as large crystals, such as silicon, used in semiconductor 
production; whether polycrystalline or amorphous films of KP.sub.15 could 
be reproducibly made and utilized for semiconductor production; and the 
full characterization of the materials produced by the vapor transport 
experiment and any analogous materials which might have the same useful 
properties. 
After many vapor transport experiments the inventors were astonished to 
find that the polycrystalline and amorphous materials that were produced 
by vapor transport where a single source of a mixture of potassium and 
phosphorus is heated and material condensed at the other end of a closed 
tube, were not KP.sub.15 but when measured by wet analysis were KP.sub.x 
where x seemed to range from about 200 to about 10,000. 
The inventors have since made the amazing discovery that the affinity of 
phosphorus for potassium, or any alkali metal for that matter, in single 
source vapor transport causes initial deposition of MP.sub.15 as the most 
stable polyphosphide. If there is an excess of phosphorus, then a new form 
of phosphorus will be deposited. (MP.sub.x where x is much greater than 
15). This new form of phosphorus has the same electronic qualities as 
KP.sub.15 and is a useful semiconductor. 
During the course of their investigations the inventors, in an effort to 
form thin films of polycrystalline and amorphous KP.sub.15 and other 
alkali metal analogs which could not be formed by single source vapor 
transport, conceived of a two source (separated source) vapor transport 
method in which the alkali metal and the phosphorus are spaced apart and 
separately heated. By controlling the temperature of a separate 
intermediate deposition zone, thin films of MP.sub.15 where M is an alkali 
metal, have been made in polycrystalline and amorphous forms. This 
technique has also led to the production of thin films of polycrystalline 
and thick films of amorphous phosphorus material of the new form, and 
other materials presumably polymer-like having the formula MP.sub.x, where 
M is an alkali metal and x is much greater than 15. 
We have also used Flash Evaporation, Chemical Vapor Deposition, and propose 
to use Molecular Flow Deposition methods for synthesizing these materials. 
We use MP.sub.x as the formula for all polyphosphides. As will be pointed 
out below, for useful semiconductors, x may range from 7 to infinity. 
Known alkali polyphosphides have the formula MP.sub.7, MP.sub.11, and 
MP.sub.15. We have discovered that presumably polymer forms exist having 
the formula MP.sub.x where x is much greater than 15. 
Also during these investigations single source vapor transport has been 
improved over the prior art by controlling the deposition temperature to 
be constant over a large area, so that large area thick films and boules 
of polycrystalline and amorphous MP.sub.x where x is much greater than 15 
have been formed. 
Large quantities of crystalline and polycrystalline MP.sub.15, where M is 
an alkali metal, have been made by isothermally heating together 
stoichiometric proportions of an alkali metal and phosphorus. This 
condensed phase method produces excellent MP.sub.x where x ranges from 7 
to 15 for use in single source vapor transport. The condensed phase method 
itself is facilitated by the prior mixing and grinding together an alkali 
metal and phosphorus in a ball mill which is preferably heated to a 
temperature in the neighborhood of 100.degree. C. This ball milling 
surprisingly produces relatively stable powders. 
All of the parallel tube polyphosphides have a band gap of approximately 
1.8 eV, photoconductivity ratios much greater than 5, (measured ratios 
have a range from 100 to 10,000), and low conductivity in the order of 
10.sup.-8 to 10.sup.-9 (ohm-cm).sup.-1. 
Since we have discovered that the amorphous forms of these materials, i.e. 
alkali polyphosphides MP.sub.x where x is greater than 6 formed in the 
presence of an alkali metal have substantially the same semiconductive 
properties, we conclude that the local order of the amorphous materials is 
the same, i.e. all parallel pentagonal tubes substantially throughout 
their extent. 
In all the polyphosphides, the 3 phosphorus-to-phosphorus (homatomic) 
covalent bonds at the majority of phosphorus sites dominate any other 
bonds present to provide the conduction paths and they all have 
semiconductor properties. 
The covalent bonds of the phosphorus atoms, all of which are used in the 
catenation providing the dominant conduction paths and the parallel local 
order in these materials, provide the good semiconducting properties. The 
phosphorus atoms are trivalent and the catenations form spirals or tubes 
having channel-like cross sections. The alkali metal atoms, when present, 
join the catenations together. Atomic species other than phosphorus, 
particularly trivalent species capable of forming 3 covalent homatomic 
bonds, should also form semiconductors. 
Thus we have invented new forms of phosphorus and methods of making the 
same, solid films of amorphous and polycrystalline MP.sub.x and methods 
and apparatus for making the same, methods and apparatus for making metal 
polyphosphides by multiple temperature single source techniques, methods 
and apparatus for making high phosphorus polyphosphides by multiple 
separated source techniques, methods and apparatus for making MP.sub.15 by 
condensed phase techniques in polycrystalline forms, semiconductor devices 
comprising polyphosphide groups of seven or more phosphorus atoms 
covalently bonded together in pentagonal tubes having a band gap greater 
than 1 eV and photoconductivity ratios of 100 to 10,000, semiconductor 
devices comprising MP.sub.x where M is an alkali metal and x is greater 
than 6, and materials having a band gap greater than 1 eV and 
photoconductivity ratios of 100 to 10,000, semiconductor devices formed of 
a high proportion of catenated covalently bonded trivalent atoms, 
preferably phosphorus, where the catenated atoms are joined together in 
multiple covalent bonds, the local order of which comprises layers of 
catenated atoms which are parallel in each layer and the layers are 
parallel to each other, the catenations preferably being pentagonal tubes, 
semiconductor devices comprising an alkali metal and said catenated 
structures wherein the number of consecutive covalent catenated bonds is 
sufficiently greater than the number of non-catenated bonds to render such 
material semiconducting, semiconductor devices formed of compounds 
comprising at least two catenated units, each unit having a skeleton of at 
least 7 covalently bonded catenated atoms, preferably phosphorus, and 
having alkali metal atoms conductively bridging the skeleton of one unit 
to another, junction devices, methods of forming such semiconductor 
devices, methods of doping such semiconductor devices, methods of 
conducting electrical current and generating electrical potential 
utilizing such devices. 
We have therefore discovered a whole class of materials to be useful 
semiconductors, some members of the class having been first produced or 
properly characterized by us, and others of which have been produced in 
the prior art with their useful semiconductor properties being unknown 
until our discoveries and inventions. 
All of these materials have a band gap within the range of 1 to 3 eV, 
preferably within the range of 1.4 to 2.2 eV and most preferably about 1.8 
eV. Their photoconductivity ratios are greater than 5 and actually range 
between 100 and 10,000. Their conductivities are within the range of 
10.sup.-5 -10.sup.-12 (ohm-cm).sup.-1, being in the order of 10.sup.-8 
(ohm-cm).sup.-1. 
Those skilled in the art will readily understand that the alkali metal 
component M of polyphosphide or any appropriate trivalent "ide" capable of 
forming homatomic covalent bonds, and having the formula MY.sub.x may 
comprise any number of alkali metals, (or combination of metals mimicking 
the bonding behavior of an alkali metal) in any proportion, without 
changing the basic pentagonal tubular structure and thus without 
significantly affecting the electronic semiconductor properties of the 
material. 
We have further discovered and invented methods of doping the materials of 
the invention utilizing doping with iron, chromium and nickel, to increase 
the conductivity. Junctions have been prepared using Al, Au, Cu, Mg, Ni, 
Ag, Ti, wet silver paint, and point pressure contacts. 
The incorporation of arsenic into the polyphosphides (all parallel tubes) 
has also been demonstrated to increase conductivity. 
These doping methods are also part of our invention and discovery. 
The semiconductor materials and devices of the present invention have a 
wide variety of uses. These include photoconductors such as in 
photocopying equipment; light emitting diodes; transistors, diodes, and 
integrated circuits; photovoltaic applications; metal oxide 
semiconductors; light detection applications; phosphors subjected to 
photon or electron excitation; and any other appropriate semiconductor 
application. 
In the course of our work we have also produced for the first time large 
crystals of monoclinic phosphorus. These crystals are obtained from vapor 
transport technique using MP.sub.15 charge or a mixture of M and P (M/P) 
in varying ratios. Surprisingly, these large crystals of monoclinic 
phosphorus contain a significant amount of alkali metals (500 to 2000 ppm 
have been observed). Under the same conditions, these crystals cannot be 
grown without the presence of alkali metals in the charge. 
Two different crystal habits have been observed for these large crystals of 
phosphorus. 
One crystal habit was identified as truncated pyramidal shape crystals as 
shown in FIG. 39. These crystals are hard to cleave. The other form is a 
platelet-like crystal and is cleavable as shown in FIG. 40. 
The largest crystals we have produced in the habit shown in FIG. 39 are 
4.times.3 mm.times.2 mm high. The largest crystals we have produced in the 
habit shown in FIG. 40 are 4 mm square and 2 mm thick. 
The crystals are metallic looking on reflection and deep red in 
transmission. Chemical analysis indicates that they contain anywhere from 
500 to 2000 parts per million of alkali metal. Their power X-ray 
diffraction patterns, Raman spectra and differential thermal analysis are 
all consistent with the prior art Hittorf's phosphorus. 
Photoluminescence of crystals grown in the presence of Cesium in FIG. 41 
and crystals grown in the presence of Rubidium in FIG. 42 show peaks at 
4019 and 3981 cm.sup.-1, which indicate a band gap of about 2.1 eV at room 
temperature for this monoclinic phosphorus. 
The crystals may be utilized as a source of phosphorus; as optical rotators 
in the red and infra-red portion of the spectrum (they are birefringent); 
as substrates for the growth of 3-5 materials such as Indium Phosphide and 
Gallium Phosphide. They may be utilized in luminescent displays or as 
lasers. 
We have grown from the same charge and deposited at a slightly lower 
temperature the star shaped fibrous crystals shown in FIGS. 44 and 45. 
We have also grown by vapor transport a crystal allotrope of phosphorus, 
the twisted fiber of phosphorus shown in FIG. 46. 
The polyphosphides may be used as fire retardants and strengthening fillers 
in plastics, glasses, and other materials. The twisted tube and star 
shaped fibers should be of particular value in strengthening composite 
materials because of their ability to mechanically interlock with the 
surrounding material. The platelets should be of particular value in thin 
sheet material where glass flakes are now employed. 
The film materials of the invention may be utilized as coatings for their 
chemical stability, fire retardant, and optical properties. 
OBJECTS OF THE INVENTION 
It is therefore an object of the invention to provide a new class of useful 
semiconductor materials. 
Other objects of the invention are to provide new methods and apparatus for 
making polyphosphides. 
Still other objects of the invention are to provide new forms of stable 
high phosphorus materials and methods and apparatus for making the same. 
Further objects of the invention are to provide new forms of phosphorus and 
methods and apparatus for making the same. 
Still other objects of the invention are to provide dopants and methods of 
doping such materials. 
Yet other objects of the invention are to provide semiconductor devices 
employing the above. 
Another object of the invention is to provide large crystals of monoclinic 
phosphorus. 
Still another object of the invention is to provide high purity phosphorus. 
Still another object of the invention is to provide new semiconductor 
materials. 
Still another object of the invention is to provide a birefringent material 
for use in the red and infra-red portion of the spectrum. 
Yet still another object of the invention is to provide methods for making 
materials of the above character. 
A further object of the invention is to provide such methods which are more 
convenient than the prior art and less expensive. 
Other objects of the invention are to provide coating materials, fillers, 
reinforcing materials, and fire retardants. 
Other objects of the invention will in part be obvious and will in part 
appear hereinafter. 
The invention accordingly comprises one or more inventive steps and the 
relation of such steps with respect to each of the others which will be 
exemplified in the methods and processes hereinafter described, 
compositions of matter possessing the characteristics, properties and the 
relationship of constituents and components which will be exemplified in 
the compositions hereinafter described, articles of manufacture possessing 
the features, properties, and the relation of elements which will be 
exemplified in the articles hereinafter described and apparatus comprising 
the features of construction and arrangement of parts which will be 
exemplified in the apparatus hereinafter described. The scope of the 
invention is indicated in the claims.

The same reference numbers refer to the same elements throughout the 
several views of the drawings. 
BEST MODE FOR CARRYING OUT THE INVENTION 
The high phosphorus materials of the invention exemplified by the high 
phosphorus polyphosphides MP.sub.15 where M is an alkali metal, and the 
new forms of phosphorus formed, are all believed to have similar local 
order, whether crystalline, polycrystalline or amorphous. We believe that 
in both crystalline and amorphous MP.sub.15, this local order takes the 
form of elongated phosphorus tubes having pentagonal cross sections as 
shown in FIGS. 4, 5 and 6. All of the pentagonal tubes are generally 
parallel on the local scale and in MP.sub.15 double layers of the 
pentagonal phosphorus tubes are connected to each other by interstitial 
alkali metal atoms. In the new forms of phosphorus of our invention, many, 
if not most of the alkali metal atoms are missing. However, it appears 
that one new form of phosphorus formed in the presence of very small 
amounts of alkali metal atoms grows from vapor deposition in the same form 
as MP.sub.15. One experiment to be discussed below indicates that at least 
one form of this is by growth of the new form of phosphorus on a layer of 
MP.sub.15. The MP.sub.15 may act as a template causing the phosphorus to 
organize in the same structure. All of the materials having these all 
parallel pentagonal phosphorus tubes have been found by us to have a band 
gap between 1.4 and 2.2 eV and most on the order of 1.8 eV. 
Photoconductivity ratios range from 100 to 10,000. Thus it is indicated 
that all high phosphorus alkali metal polyphosphides from MP.sub.7 through 
MP.sub.15 and more complex forms and mixed polymers of MP.sub.15 and the 
new form of phosphorus discovered by us (MP.sub.x where x is much greater 
than 15), which all have the all parallel pentagonal tube structure, if 
stable, will be useful semiconductor materials, barring the inclusion of 
elements that would act as traps, cause the formation of grain boundaries, 
or the like. 
In all of these materials having the all parallel pentagonal tubular 
structure, our investigations indicate that the multiple continuous 
covalent phosphorus-to-phosphorus bonds of the tubes being substantially 
greater in number than the number of other bonds will provide primary 
electrical conduction paths for electrons and holes and thus provide good 
semiconductor properties. It is further our opinion that the presence of 
alkali metals in the charge, even when resulting in trace amounts in the 
new forms of phosphorus we have discovered, promote growth of the maerials 
in forms that maintain the same structural and electronic properties as 
KP.sub.15 or as monoclinic phosphorus, depending on deposition conditions. 
The family of semiconductor members to which the subject invention is 
directed comprises high phosphorus polyphosphides having the formula 
MP.sub.x wherein M is a Group 1a alkali metal, and x is the atomic ratio 
of phosphorus-to-metal atoms, x being at least 7. Metallic elements of 
Group 1a most suitable are Li, Na, K, Rb, and Cs. Although francium 
presumably is suitable, it is rare, has not been involved in any known 
synthesis of MP.sub.x and is radioactive. High phosphorus polyphosphides 
where M includes Li, Na, K, Rb or Cs have been formed and tested by the 
inventors. 
The polyphosphide compounds of this invention as presently defined must 
contain an alkali metal. Some of the new forms of phosphorus must be 
formed in the presence of minor amounts if not unmeasurable amounts of 
alkali metal. However, other metals may be present in minor amounts as, 
for example, dopants or impurities. 
KP.sub.15 and, as we later learned, a new form of phosphorus was first 
synthesized as follows. 
Referring to FIG. 1, a two temperature zone furnace 10 comprises an outer 
sleeve 12 preferably constructed of iron. Outer sleeve 12 is wrapped in a 
thermally insulative coating 14 which can comprise an asbestos cloth. The 
furnace was constructed in the laboratory shop of the inventors. 
We used a P/K atom ratio of about twelve (12) as reactants 36 in furnace 
10. As one illustrative example, 5.5 g of red phosphorus and 0.6 g of 
potassium were transferred under nitrogen to quartz tube 32. Prior to 
transfer, the phosphorus was washed repeatedly with acetone, and air 
dried. However, this washing is considered optional, as is the solvent 
selected. 
After being charged with reactants 36, tube 32 was evacuated to, for 
example, 10.sup.-4 Torr, sealed, and then placed in furnace 10. Tube 32 
was mounted at a slight incline in the furnace. Power supplied to 
conductors 24 and 26 was adjusted to establish a temperature gradient of, 
for example, 650.degree. C. to 300.degree. C. from heat zone 28 to heat 
zone 30. With the above described inclination of furnace 10, reactants 36 
were assured of being located in the hotter temperature heat zone 28. 
After maintaining furnace 10 at these conditions for a sufficient period of 
time, for example approximately 42 hours, power to conductors 24 and 26 
were terminated and tube 32 was allowed to cool. Upon reaching ambient 
temperature, tube 32 was cut open under a nitrogen atmosphere and the 
contents of tube 32 were removed. The contents were washed with CS.sub.2 
to remove pyrophoric materials, leaving approximately 2.0 g of stable 
product. This resulted in a yield of approximately 33 percent. 
Using this form of synthesis, various phases of resultant product occur at 
well defined positions within tube 32 as illustrated in FIG. 2. A dark 
gray-black residue 40 coupled with a yellow-brown film 42 is typically 
produced at the extreme end of hot zone 30, where reactants 36 are 
initially located. Moving in a direction of decreasing temperature along 
tube 32, there is next found black to purple film deposits 42 which are a 
polycrystalline material. Next to film deposits 42 is an abrupt dark ring 
of massed crystallites 44 and immediately adjacent crystallites 44 is a 
clear zone wherein whiskers 46 are grown. A highly reflective coating or 
film deposit 48 is found on the lower portion of tube 32 in the beginning 
of cold zone 28. Above film deposit 48 a deep red film deposit 50 
occasionally occurs depending on the temperature maintained in the zone. 
The deposits 48 and 50 can be polycrystalline, amorphous or a mixture of 
polycrystalline and amorphous material depending on the reactants and 
temperature. At the extreme end of cold zone 28 is a mass or film deposit 
52 which is amorphous material. 
Since there is a continuous temperature gradient from the hot zone to the 
cold zone of the reaction tube shown in FIGS. 1 and 2, the nature of the 
materials deposited actually varies continuously from high quality 
crystalline whiskers to polycrystalline to amorphous. In order to 
manipulate the reaction and attempt to deposit large areas of uniform 
layers of material, a three zone furnace was constructed and is 
illustrated in FIG. 3. As herein embodied, the three zone furnace 54 is 
essentially identical to furnace 10 illustrated in FIG. 1, in that furnace 
54 comprises an outer iron sleeve 56, a tube 60, and a reaction tube 58. 
For purposes of simplicity, asbestos wrappings of outer sleeve 56 and tube 
58 have been omitted from FIG. 3. Furnace 54 is primarily distinguishable 
from furnace 10 in that tube 58 is much longer in comparison to tube 32, 
and is preferably on the order of 48 cm in length. In addition, furnace 54 
has associated with it three distinct heat zones, 62, 64 and 66 which are 
individually controllable to create a more definitive heat gradient along 
tube 60. Tube 60 may be supported by asbestos blocks 68 and 70 in a manner 
so as to provide for an inclination of tube 60 and reaction tube 58 toward 
heat zone 62, in order to keep reactants 36 in proper position. 
Very good quality preparation of KP.sub.15 whiskers were obtained using 
temperature set points of 550, 475, and 400 degrees centigrade in heat 
zones 62, 64 and 66 respectively. It was also found that bulky deposits 
generated in furnace 10, when loaded into inner sleeve 60 of furnace 54 
and reheated in the above-identified temperature gradient, would sublime 
to form film deposits like those of films 48-52 illustrated in FIG. 2, but 
only when a high zone temperature of at least 400.degree.-475.degree. C. 
was used. 
Unit cell structural information on KP.sub.15 crystals produced in 
accordance with the method described above was obtained by single crystal 
X-ray diffraction data, and collected with an automated diffractometer. A 
fibrous single crystal of 100 microns diameter was selected and mounted on 
a glass fiber. The structure was determined by direct methods using a 
total of 2,544 independent reflections. All the atoms were located by an 
electron map and differential Fourier synthesis. 
Typical needle-like crystals were examined by high magnification and 
scanning electronic microscopy (SEM). The resultant SEM photographs of the 
cross section of the needles show that the needles are apparently composed 
of dense fibrils rather than hollow tubes. Marked twinning of the whisker 
crystals is also discernible on the microphotographs of KP.sub.15 whiskers 
in FIGS. 7 and 8. The diameter of the primary fibrils of the whisker-type 
crystals is estimated to be approximately 0.1-0.2 microns. Larger fibrils 
seem to have a fine structure consisting of parallel lamellae of 
approximately 500 angstroms thickness. 
From the initial crystal data refinement study, the stoichiometry of the 
studied potassium phosphide compound appears to be KP.sub.15. 
The phosphorus atomic framework of the compound is formed of identical unit 
tubes with a pentagonal cross section. The tubes are unidimensional along 
the needle axis direction. The phosphorus tubes are parallel to one 
another. In the simplest description, double layers of separated 
phosphorus tubes are connected by a layer of potassium atoms. As judged by 
the inter atomic distances, the K atoms are at least partially ionically 
bonded to P atoms. A cross sectional view of a whisker is presented in 
FIG. 5. 
More specifically, each potassium site is associated with a rigid unit of 
15 consecutive phosphorus atoms having a structure as illustrated in FIG. 
4. In this rigid unit all the phosphorus atoms but one are bound to three 
other phosphorus atoms. The other phosphorus atoms are chained, with the 
missing bonds linked to a potassium atom as shown in FIG. 5. Thus, the 
potassium atom appears to link tubular phosphorus units through a missing 
P-P bridge. In the investigated structure, potassium has phosphorus atoms 
as nearest neighbors at distances of 3.6A, 2.99A and 2.76A, respectively. 
The P-P distances vary from 2.13A to 2.58A. The bond angles at the 
phosphorus chains vary between 87.degree. to 113.degree. and average 
102.degree.. 
Arsenic forms a layered structure having an average bonding angle of 
98.degree. and this is not known to be a useful semiconductor. Black 
phosphorus has a similar structure and an average bonding angle of 
96.degree.. Trivalent atoms which can form their three bonds within the 
range of 87.degree. to 113.degree. with the average above 98.degree. may 
form the same catenated structure as MP.sub.x. If the bonds are covalent 
the material can be expected to have the same electronic properties as 
MP.sub.x. 
Table I gives the crystal lattice parameters and atomic positions we found 
for crystalline KP.sub.15. 
TABLE I 
______________________________________ 
Crystal Lattice Parameters For KP.sub.15 
______________________________________ 
Triclinic system 
Unit cell parameters 
a = 9.087 A.degree. (.+-.0.15) A.degree. 
b = 11.912 A.degree. (.+-.0.10) A.degree. 
c = 7.172 A.degree. (+0.15) A.degree. 
.alpha.= 
101.4 (.+-.0.1).degree. 
.beta.= 
107.9 (.+-.0.2).degree. 
.delta.= 
89.3 (.+-.0.1).degree. 
______________________________________ 
The unit cell is primitive with one molecule per unit cell and a volume of 
723.3 Cubic Angstroms 
SE GROUP P.sub.1 
The highest attainable symmetry in the above structural configuration is a 
centrosymmetric P.sub.1 space group with the stoichiometry given by 
KP.sub.15. 
The corresponding X-ray powder diffraction data for KP.sub.15 
polycrystalline material with copper illumination is shown in FIG. 9. This 
shows the d spacing with the corresponding X-ray intensities. 
Similar X-ray powder diffraction data have been observed for whiskers and 
polycrystalline MP.sub.15 materials with M=Li, Na, K, Rb and Cs. 
In all these isostructural compounds, the structural framework can be 
viewed as formed of parallel pentagonal phosphorus tubes. These tubes are 
linked by a P-M-P bridge. 
The rigid units for this type of structure are P.sub.4 and MP.sub.3. The 
building block for the atomic framework can be viewed as [P.sub.4 
-MP.sub.3 ] or [MP.sub.7 ]. 
Therefore: 
EQU [MP.sub.7 ]+2[P.sub.4 ].fwdarw.[P.sub.4 -MP.sub.7 -P.sub.4 ] 
which represents the basic structure MP.sub.15. 
Of course, one of the building blocks in such compounds may be present in 
much larger quantities than the other. In the case of MP.sub.x, for 
example, there may exist building blocks of [MP.sub.7 ] and [P.sub.8 ], 
which are present in a ratio of a to b, respectively. In such a case 
MP.sub.x could be expressed in the form [MP.sub.7 ].sub.a [P.sub.8 
].sub.b, wherein mathematically x=(7a+8b)/(a). 
It is also possible for a compound to have b much greater than a and have 
the same basic structural framework. 
This type of polymer-like tubular structure will result in "fibers" or 
whiskers of the type MP.sub.x with x much greater than 15. 
Whiskers and polycrystalline "fibers" of the type MP.sub.x with x greater 
than 1000 (M=Li, Na, K, Rb, Cs) have been observed to crystallize at low 
temperature (about 400.degree. C.) using the vapor transport technique. 
The X-ray powder diffraction data of these materials are substantially the 
same. Data for KP.sub.x where x is much greater than 15 under copper 
illumination is shown in FIG. 10. 
We can compare the structure described above to other structures based on 
pentagonal cross section phosphorus tubes. The KP.sub.15 compound is 
isostructural to LiP.sub.15, NaP.sub.15, RbP.sub.15, CsP.sub.15. The other 
alkali metals appear to play the same role as K. 
From structural data we concluded that numerous compounds can be formed 
which will be based on pentagonal cross section tubular building blocks. 
We also found that in phosphorus materials, at least partially, the 
phosphorus atoms can be replaced by other pnictides, such as As, Bi or Sb. 
Substitution under 50 atom percent is possible, without adversely 
affecting the basic structure of the high phosphorus polyphosphides. 
In Table II are shown the various MP.sub.x compounds synthesized that we 
have found the same structure as crystalline KP.sub.15 as shown by XRD 
powder diffraction fingerprint analysis. 
TABLE II 
______________________________________ 
Rigid units MP.sub.3 and P.sub.4 
Building blocks [P.sub.4 --MP.sub.3 ] or [MP.sub.7 ] and [P.sub.8 ] 
Basic structure [P.sub.4 --MP.sub.7 --P.sub.4 ] or [MP.sub.15 ] 
M: Li, Na, K, Rb, Cs 
Compounds Isostructural With Crystalline KP.sub.15 
______________________________________ 
EQU M.sub.x M'.sub.1-x P'.sub.y P.sub.15-y 
with: 
EQU 0.ltoreq..times..ltoreq.1 
EQU y&lt;7.5 
M and M' from Group 1a 
P' from Group 5a (As, Bi, Sb) 
Initially the inventors found, as previously stated, that the crystalline 
whiskers produced in the apparatus of FIGS. 1, 2 and 3 were MP.sub.15. 
However, analysis of the polycrystalline and amorphous materials, although 
indicating that these materials had the same semiconducting properties as 
the MP.sub.15 whiskers, had widely variable stoichiometric proportions 
from MP.sub.200 to MP.sub.10,000, and surprisingly no manipulation of the 
temperatures in the three zone furnace illustrated in FIG. 3 would produce 
amorphous forms of MP.sub.15. It was therefore necessary to greatly refine 
the methods of producing these materials and to invent a new two source 
vapor transport apparatus in order to successfully produce polycrystalline 
and amorphous MP.sub.15 materials. The very high x materials which are now 
thought to be a new form of phosphorus, have also been prepared by this 
method by initially depositing MP.sub.15 and thereafter cutting off the 
source of alkali metal so that only phosphorus vapor is present for 
deposition of phosphorus. Additionally, a condensed phase process has been 
extensively investigated using molar charges of MP.sub.x materials where x 
varies from 7 to 15. In this method the stoichiometric mixtures are 
heated isothermally to reaction and then cooled. We have produced a wide 
variety of MP.sub.x materials in this manner which are crystalline or 
polycrystalline powders. 
There follows a detailed description of the methods we have employed to 
synthesize high phosphorus materials and how we have measured the 
electro-optical characteristics and demonstrated that they are useful 
semiconductors. 
PREATION OF STABLE HIGH PHOSPHORUS MATERIALS BY THE VAPOR TRANSPORT 
TECHNIQUE FROM A SINGLE SOURCE 
Introduction 
The technique of applying sufficient energy to a system to create vapor 
species which yield products on condensation or deposition, at appropriate 
temperatures, is called "vapor transport". For the following discussion, 
where the source materials are held in close contact and heated together 
at about the same temperature, the further description as a "single 
source" technique is applicable. 
The methodology described by Von Schnering was essentially a single-source 
vapor transport technique, although the charge sometimes consisted of 
separate ampoules of metal and phosphorus heated to nearly the same 
temperatures. However, the flow of vapor species to the deposition zones 
was effectively the same as when the metal and the phosphorus are first 
mixed together. More specifically, in single source vapor transport the 
vapor species are first brought together at a high temperature and then 
are deposited at a lower temperature. 
The following indicates our development of the technique as it has been 
applied to the preparation of alkali metal polyphosphides and the 
departure from von Schnering's method, which results in improved, more 
selective preparation of: crystalline metal polyphosphides of the type 
KP.sub.15 ; low alkali-metal content polyphosphides, polycrystalline 
material, of the type KP.sub.x, where x is much greater than 15; and a new 
form of amorphous phosphorus, in which the alkali metal content can be 
less than 50 ppm (parts per million). 
The studies we have made fall into several categories: type of charge, 
charge ratio, tube length and geometry, and temperature gradient profile. 
The following examples illustrate the temperature dependent product 
deposition relationships we have discovered and our improved temperature 
controlling methods that result in the selective preparation of desired 
products. 
General Methods: 
An alkali metal and red phosphorus are sealed in quartz tubes, at reduced 
pressures (about 10.sup.-4 Torr). Atom ratios of the two elements range 
from P/M=5/1 to 30/1, with 15 to 1 as the most common charge. The elements 
are generally ball-milled together, prior to loading in the quartz tubes. 
The millings are carried out with stainless steel balls and mills and last 
for at least 40 hours. The mills are usually heated to 100.degree. C. for 
the duration of the milling, to assist in the dispersion of the metal in 
the red phosphorus powder. 
The milling achieves an intimate contact of the two elements in as 
homogeneous a manner as possible. The products of the milling are 
generally fine powders which are easily manipulated in a dry box and may 
be stored with little noticeable deterioration. The powders show 
remarkable stability when exposed to air and moisture, compared to the 
stability of their constituents, especially the alkali metals. For 
instance, direct addition of water to the powders only results in 
combustion of materials in random cases and on a small scale. 
PREATION OF MP.sub.15 SINGLE CRYSTALS, POLYCRYSTALLINE AND AMORPHOUS 
MATERIALS 
A mixture of the elements (alkali metal and red phosphorus) is sealed at 
reduced pressure (less than 10.sup.-4 Torr) in a quartz tube 58 (FIG. 3), 
about 50 cm long by 2.5 cm in diameter. Tube 58 is supported inside the 
heating chamber of a Lindberg Model 24357 3-zone furnace in one of two 
ways. One method employs a second quartz tube 60 as a support piece, which 
is, in turn, held in the chamber, away from the heating elements, by 
asbestos blocks 68 and 70, such that the coupled tubes rest at an incline, 
insuring the reactants remain in the hottest zone. The other method (FIG. 
14) is to use supports built of woven tape 137,139 wrapped about the 
reaction tube in an expanding spiral, an inch wide, and filling the 
circular cross section of the heating chamber. This woven tape may be made 
of a variety of materials: Asbestos, Fiberfrax (from Carborundum Company), 
or woven-glass. The latter is preferred primarily on safety and 
performance criteria. The implications of using the two different methods 
are described below. 
The reactants are driven to products by applying energy to the system via 
the resistance elements of the furnace. If a sufficiently high temperature 
is applied to the reactants, while other portions of the tube are held at 
appropriate lower temperatures, products will deposit, or condense, from 
vapor species. The temperature differential which drives this so-called 
"vapor-transport" synthesis, is achieved in a 3-zone furnace by selecting 
different setpoint temperatures for the individually controlled heating 
elements. 
METHOD 1. See FIG. 3. The 50 cm tube, containing the reactants, is held by 
the second quartz tube in the 61 cm long heating chamber. Application of a 
thermal gradient by manipulation of the 3 set-points results in a 
generally linearly-falling gradient. That is, the slope of the gradient, 
.DELTA.T/d, where T is temperature and d is distance along the chamber, is 
approximately constant between the centers of the two outside heating 
elements. This linear gradient, applied over the long dimensions of the 
tube, functions to cleanly separate the variety of product materials 
formed in the reaction. The products occur in a characteristic pattern of 
decreasing temperature of deposition: dark purple to black polycrystalline 
films; a ring of massed crystallites; "single" crystals or whiskers; red 
films of small-grain, polycrystalline morphology; and, at coldest 
temperatures, dark grey amorphous material. 
A series of experiments have shown that the amorphous material will not 
form in these sealed tubes if the coldest temperature is greater than 
about 375.degree. C. Similarly, the occurrence of the red polycrystalline 
material could be greatly reduced by keeping the lowest temperatures at or 
above 450.degree. C. 
We have also found that polycrystalline MP.sub.15 will not form in single 
source apparatus. The polycrystalline and amorphous materials formed are 
all high x materials where x is much greater than 15. 
METHOD 2. The woven tape holders serve not only to orient the reaction tube 
but also as effective barriers to heat-transfer between the three heating 
zones. These barriers give rise to steeper drops between the zones, but a 
flatter gradient within the center zone. The result is a step-like 
temperature profile, which can be manipulated to selectively produce 
products by providing appropriate ranges of deposition temperatures. 
A. Determination of Product Deposition Temperatures 
In von Schnering's announcement of the preparation of single crystals 
(whiskers) of KP.sub.15, he described the preparation from the elements as 
entailing the heating of the elements--potassium and red phosphorus--in a 
"temperature gradient" of "600/200.degree. C.", in a 20 cm or so quartz 
tube. He further states the crystals form at "300.degree. to 320.degree. 
C.". The furnaces used were apparently single element furnaces in which 
the gradient arises via heat loss from one end of the tubes sticking out 
of the furnace. 
In the first improvement on this procedure, a three-zone furnace as shown 
in FIG. 3, with independently controlled heating elements, and a 61 cm 
long heating chamber (Lindberg Model 54357 3-zone furnace) was employed, 
to achieve and control the applied gradient. By supporting the reaction 
tube, which was not extended to approximately 52 cm long, in a second, 
open quartz tube, which was, in turn, supported by asbestos blocks, a 
generally linear temperature gradient, .DELTA.T/d, was approximately 
constant between the centers of the two outside heating elements. The 
power to these elements were controlled by a Lindberg Model 59744-A 
Control Console, which uses three, independent SCR-proportional band 
controllers to maintain the temperatures selected on manually set 
thumb-wheels. 
The linearly-falling gradient, applied over the long dimensions of the 
reaction tube, served to cleanly separate the variety of product materials 
formed in the reaction. The products occur in a characteristic pattern of 
decreasing temperature of deposition: dark purple to black polycrystalline 
films; a ring of massed crystallites; single crystals or "whiskers"; red 
films of small-grain, polycrystalline morphology, and, at the coldest 
temperatures, dark grey, amorphous materials. 
EXAMPLE I 
A Lindberg Model 54357 3-zone furnace as shown in FIG. 3 comprising heating 
elements embedded in a refractory material in separate cylindrical 
sections of 15.3 cm, 30.6 cm and 15.3 cm lengths, for a total heating 
chamber length of 61 cm, was used for this example. The diameter of the 
chamber is 8 cm. Controlling thermocouples (not shown) are located at 
about 7.0, 30.5, and 53.5 cm along the 61 cm length. 
The ends of the heating chamber were plugged with glass wool to minimize 
heat loss from the furnace. A 60 cm long by 4.5 cm diameter quartz tube 
was held at a slight angle, by asbestos blocks, in the heating chambers. 
The quartz reaction tube was round bottomed, 49 cm long by 2.5 cm in 
diameter, and reduced to a narrow addition tube 10 cm long by 1.0 cm wide. 
Under a dry nitrogen atmosphere, 6.51 g of red phosphorus and 0.62 g of 
potassium were transferred into the tube. The atom to atom ratio of 
phosphorus to metal was 13.3 to 1. The phosphorus was reagent grade (J. T. 
Baker). The tube was evacuated to 10.sup.-4 Torr and sealed by fusing the 
addition tube several cm's from the wider part of the tube such that the 
total length was 51.5 cm. The sealed tube was placed in the 3-zone furnace 
as described above and the set point temperatures of the three zones 
brought to 650.degree. C., 450.degree. C., and 300.degree. C. over a 
period of 5 hours, and held there for another 164 hours. The power was 
shut off and the oven allowed to cool to ambient temperatures at the 
inherent cooling rate of the furnace. The tube was cut open under a dry 
nitrogen atmosphere in a glove bag. The products consisted of crystalline, 
polycrystalline, and amorphous forms. 
In Table III, the different processing parameters used for several other 
runs are listed, along with the types of products observed in each run. 
Prior to being cut open, the tubes from the first three runs were 
inspected as to the positions along the tubes of several products: the 
dark ring of massed crystallites, and the start of red polycrystalline 
films. The whiskers were always observed between these two points. These 
positions were later correlated to the temperatures along the gradients 
created by the noted set points. These data are recorded in Table IV. 
TABLE III 
__________________________________________________________________________ 
P/M Time Tube 
Ref. 
Charge 
M P Press. 
T.sub.1 
T.sub.2 
T.sub.3 
Hours Length 
No.* 
Ratio.sup.a 
grams 
grams 
Torr.sup.b 
.degree.C. 
.degree.C. 
.degree.C. 
VT/Total.sup.c 
cm Products.sup.d 
Remarks 
__________________________________________________________________________ 
1 13.3 
0.21 (K) 
6.51 
1 .times. 10.sup.-4 
650 
450 
300 
164/172 
51.5 
S.C., P.C., a 
Exam- 
ple I 
2 12.5 
0.67 (K) 
6.56 
1 .times. 10.sup.-3 
600 
465 
350 
138/147 
52.0 
S.C., P.C., a 
3 15.1 
0.67 (K) 
8.02 
5 .times. 10.sup.-4 
550 
475 
400 
236/245 
52.0 
S.C., P.C. 
Tube 
approx failed 
4 15.0 
0.29 (Na) 
5.86 
7 .times. 10.sup.-5 
600 
450 
375 
72 S.C., P.C., a 
5 30.0 
0.15 (Na) 
6.00 
1 .times. 10.sup.-5 
600 
460 
350 
100.5 S.C., P.C., a 
0.55 (Rb) 
__________________________________________________________________________ 
.sup. a Atom to atom 
.sup.b Pressure at seal off, in Torr 
.sup.c Where one time is shown, it is the time at the noted gradient 
Where two times are shown the second is the total residence time in the 
furnace 
.sup.d S.C. = single crystal (or whisker, as often referred to) 
P.C. = Polycrystalline material, normally thick films (greater than 10 
microns) 
a = Amorphous material 
*The same reference numbers are used to refer to the same runs throughout 
the tables 
TABLE IV 
__________________________________________________________________________ 
Position of High .times. Products as a Function of Set Temperatures in 
3-Zone furnace 
Deposit 
Zone 
Ref. Length 
Temp. 
No. 
Profile 
T.sub.1 
T.sub.2 
T.sub.3 
Time 
Ring Temp. 
Films 
Temp. 
cm Range 
__________________________________________________________________________ 
1 1 650 
450 
300 
7 days 
26.0 cm 
475.degree. C. 
30.0 cm 
435.degree. C. 
4 cm 
40.degree. C. 
2 2 600 
465 
350 
5 days 
26.5 cm 
485.degree. C. 
33.0 cm 
450.degree. C. 
6.5 
cm 
35.degree. C. 
3 3 550 
475 
400 
10 days 
23.5 cm 
505.degree. C. 
36.5 cm 
460.degree. C. 
13.0 
cm 
45.degree. C. 
3 4 610 
485 
400 
3 days 
26.0 cm 
510.degree. C. 
34.5 cm 
455.degree. C. 
13.5 
cm 
55.degree. C. 
3 5 615 
485 
400 
3 days 
28.5 cm 
495.degree. C. 
42.0 cm 
450.degree. C. 
13.5 
cm 
45.degree. C. 
__________________________________________________________________________ 
Profiles 1, 2 and 3 were all used independently on separate samples to 
produce products. 
Profiles 4, and 5 are reheating profiles used on the reaction run Ref. No 
3 originally using profile 3 
Whiskers were found growing in all samples in the space between the ring 
and the deposited films. 
Temperature readings are estimated accurate to .+-. 5.degree. C.. 
Position readings are estimated accurate to .+-. 0.5 cm. 
The information from these two tables was used to establish the 
relationship of temperature and product-type. The single crystals of 
KP.sub.15 appear to form over a temperature range of about 
40.+-.10.degree. C., the center of which varies from run to run, but which 
lies around 465.degree.-475.degree. C. Similarly, the onset of deposition 
of red, polycrystalline materials appears to be about 450.+-.10.degree. C. 
Finally, amorphous material deposited even when the lowest temperature was 
around 350.degree. C. When this was raised to 400.degree. C., no amorphous 
material was observed. (Although the run in which this temperature was 
used eventually ended in a failure of the reaction tube, before products 
could actually be harvested, this temperature-product relationship for the 
amorphous material was confirmed in later runs using more advanced 
techniques). Assuming a mid-range value, an upper limit for deposition of 
amorphous material was taken as about 375.degree. C. The pressures in the 
heated tubes were not measured. 
B. Temperature Gradients Which Favor Growth of Single Crystals (Whiskers) 
Using the knowledge of the deposition temperature-product morphology 
relationships of Tables III and IV, improvements in the synthetic 
technique were sought which would allow greater selectivity of product 
type. Methods were sought for manipulating the temperature profiles in the 
furnaces which would result in larger areas of the tube surface being 
within the appropriate temperature ranges for given products. Several 
available materials with low thermal conductivities, and in easily 
manipulatable forms were checked for use as barriers to heat transfer in 
the furnaces. Woven tapes of asbestos proved a suitable product for both 
supporting the reaction tubes and creating complex gradients, consisting 
of areas of fairly flat, or isothermal, temperatures, separated by areas 
(across the barriers) of steep drops or gradients. These so-called 
"step-like" profiles were applied in all the subsequent examples where 
specific products were being sought in maximum yields. 
Another improvement which helped gain more reproducible temperature 
profiles from run to run was to use a more solid, ceramic type of material 
to fill the gaps in the heating chamber walls. In early runs, these were 
plugged with glass wool, which helped stem loss of heat, but not very 
efficiently. The large cylindrical gaps are present in the chamber walls 
because the furnaces are actually designed to hold a process tube along 
its length, for flow-through applications, rather than for enclosed 
systems, as are being run in these methodologies. 
The following examples were all aimed at trying to promote growth of single 
crystals, both larger in size, and in greater yields, both as a percentage 
of product forms, and in absolute yields. These results were indeed 
achieved. 
EXAMPLE II 
A Lindberg Model 54357 3-zone furnace identical in design and size as that 
of Example I was also used in this example. The elements were likewise 
driven by the same manually set model 59744-A Control Console. The ends of 
the heating chamber were plugged with a heat resistant ceramic-like 
material, to minimize heat loss from the furnace. The reaction tube was 
supported in the heating chamber by two rings of woven tape of asbestos. 
One of these was located between 16-19 cm and the other between 42 and 45 
cm along the chamber. This put both rings completely inside the center 
heating section, just beside the junctions of the center elements and 
those of the two outer sections. The rings were constructed such that the 
tube was held at a slight angle. The ring served to insulate the heating 
zones from each other by acting as barriers to heat transfer. 
The quartz reaction tube (FIG. 3) was round bottomed, 48 cm long by 2.5 cm 
in diameter, and reduced to a narrow addition tube 162, 10 cm long by 1.0 
cm wide. Under a dry nitrogen atmosphere, 5.47 g of red phosphorus and 
0.50 g of potassium were transferred into the tube. The atom to atom ratio 
of phosphorus to metal was 15.1. The phosphorus was 99.9999% pure. The 
potassium was 99.95% pure. The tube was evacuated to 10.sup.-4 Torr and 
sealed by fusing the addition tube several cm's from the wider part of the 
tube such that the total length was 52 cm. The sealed tube was placed in 
the 3-zone furnace as described above and the set point temperatures of 
the three zones brought to 600.degree. C., 475.degree. C. and 450.degree. 
C. over a period of 4 hours, and held there for another 76 hours. The 
power was shut off to all three zones at once and the oven allowed to cool 
to ambient temperatures at the inherent cooling rate of the furnace. The 
tube was cut open under a dry nitrogen atmosphere in a glove bag. The 
products consisted of crystalline and polycrystalline forms. 
Table V lists the processing parameters for a number of other such runs 
(data for the above example are from the run with reference number 10). 
TABLE V 
__________________________________________________________________________ 
P/K Tube 
Charge 
Grams 
Grams 
Press. 
T.sub.1 
T.sub.2 
T.sub.3 
Time Length 
Ref. No. 
Ratio.sup.a 
K P Torr.sup.c 
.degree.C. 
.degree.C. 
.degree.C. 
VT/Total.sup.d 
cm 
__________________________________________________________________________ 
6 15.1 
0.58 6.80 
7 .times. 10.sup.-4 
600 
485 
450 
24/28 50 
7 4.93 
1.54 6.01 
1 .times. 10.sup.-3 
600 
485 
450 
96/106 
about 48 
8 4.98 
1.53 6.03 
7 .times. 10.sup.-4 
600 
475 
450 
96/106 
about 49 
9 15.1 
0.50.sup.b 
5.98.sup.b 
1 .times. 10.sup.-4 
600 
475 
450 
144/ 52.5 
10 15.1 
0.50.sup.b 
5.97.sup.b 
1 .times. 10.sup.-4 
600 
475 
450 
144/ 52.0 
11 30.3 
0.25 6.00 
5 .times. 10.sup.-4 
600 
470 
450 
72/78 51.0 
12 29.7 
0.27 6.36 
1 .times. 10.sup.-5 
600 
470 
450 
72/78 51.0 
13 14.3 
0.18 (Rb) 
5.70 
1 .times. 10.sup.-5 
550 
475 
400 
about 50.0 
144/ 
14 15 0.30 (Na) 
6.12 
7 .times. 10.sup.-5 
600 
450 
375 
72/ about 50 
15 7 0.19 (Li) 
5.87 
7 .times. 10.sup.-5 
600 
450 
450 
72/184 
about 50 
__________________________________________________________________________ 
.sup.a atom to atom 
.sup.b high purity materials K, 99.95% P, 99.9999% 
.sup.c pressure at sealoff Torr 
.sup.d time at gradient/total resident time in hours 
All of these runs resulted in crystalline and polycrystalline forms. The 
yields of the single crystals were always greater than in Example I. The 
polycrystalline materials were always in the form of films deposited in 
the colder ends of the tubes and were usually limited to the last 10 or so 
cm of the tube, though there was usually some overlap with the single 
crystals. Single crystals from these runs were characterized by X-ray 
powder diffraction patterns as having the same structure as KP.sub.15 as 
determined from XRD data. Wet chemical analysis of the crystals were 
difficult to obtain with great accuracy, in part because of their 
stability, which required extreme conditions for digesting the materials 
for analysis. (See the tables VIII through XI on analytical data below) 
The polycrystalline films were also characterized by X-ray powder 
diffraction methods and wet methods. The films showed varying degrees of 
crystallinity, and the patterns were similar in several aspects to that of 
KP.sub.15, but yet were distinctly different in others. Furthermore, the 
wet analysis, coupled with frame emission spectroscopy consistently showed 
the alkali metal content to be in the part per million range (i.e. less 
than 1000 ppm and often less than 500 ppm), and with P/K ratios ranging 
from about 200 to 1 to about 5000 to 1. 
C. Thermal Gradients Which Favor Growth of Polycrystalline and Amorphous 
Materials 
Following the successful improvements in production of single crystal 
materials, a similar series of experiments was carried out to manipulate 
the 3-zone furnace and asbestos rings to find the stepped thermal 
gradients appropriate to selectively produce the polycrystalline and 
amorphous materials observed in earlier runs. 
These earlier runs suggested the temperatures necessary for obtaining the 
desired products. What remained to be shown was how to optimize these 
products. Table VI shows the type of profiles used and the products 
observed. 
TABLE VI 
__________________________________________________________________________ 
P/K Tube 
Charge K P Press. 
T.sub.1 
T.sub.2 
T.sub.3 
Time 
Length 
Products Observed.sup.f 
Ref. No. 
Ratio.sup.a 
grams 
grams 
Torr.sup.d 
.degree.C. 
.degree.C. 
.degree.C. 
Hours.sup.e 
cm W P a 
__________________________________________________________________________ 
16 K/P.sub.15.sup.b 
0.50.sup.b 
5.63.sup.b 
3 .times. 10.sup.-4 
600 
465 
350 
72/96 
51.0 
X* 
X X 
17 K/P.sub.5 
1.43 
5.66 
5 .times. 10.sup.-4 
600 
425 
400 
72/96 
50.5 
X X none 
4 K/P.sub.5 
1.49 
5.40 
7 .times. 10.sup.-4 
600 
375 
350 
72 about 
X X questionable 
50 
18 K/P.sub.5 
1.52 
6.00 
1 .times. 10.sup.-5 
600 
350 
350 
99.5 
24.0 
X X questionable 
19 K/P.sub.5 
1.25 
4.95 
5 .times. 10.sup.-4 
600 
225 
225 
50/77 
37.0 
X X small amount 
thin film 
20 K/P.sub.15.sup.b 
(6.1-BM).sup.b,c 
5 .times. 10.sup.-4 
600 
440 
325 
72/124 
47.0 
X X questionable 
__________________________________________________________________________ 
.sup.a atom to atom ratio 
.sup.b pure starting elements 
.sup.c BM -- ball milled mixture 
.sup.d pressure at seal off 
.sup.e time at gradient/total time in furnace 
.sup.f W -- whiskers (single xtal) 
P -- polycrystalline films 
a -- amorphous material 
*Product observed 
The first run, which is the subject of the Example III, just duplicated the 
temperatures of the ranges used in Example I, the linear falling gradients 
now changed to a stepped gradient. Not surprisingly, all product types 
were found, with some variation in quantity, compared to those of section 
A. When the coldest temperature was raised to 400.degree. C., as in the 
second run of Table VI, no amorphous material was found, as anticipated. 
With the 425.degree. C. center-section temperature, however, nearly 
two-thirds of the tube's interior was covered with polycrystalline films, 
and only a small number of whiskers were found, meaning the films could be 
produced almost exclusively. 
In the third and fourth runs, though, where the coldest temperatures were 
held at 350.degree. C. (cold enough for amorphous material to be formed in 
the first run), and the center zone temperatures were lowered to 
375.degree. and 350.degree. C., the amorphous materials were not formed in 
large amounts at all. Instead, large amounts of both single crystals and 
polycrystalline material were found over a fairly short space of the tube, 
and at best, only thin films of amorphous materials may have formed in the 
rest of the tubes. The same phenomenon was observed in the next two runs 
as well, although there were definitely thin amorphous films in one run. 
Apparently most vapor species are condensed out in the polycrystalline and 
single crystal forms and no significant vapor travels to the region which 
is cold enough to form amorphous forms. 
EXAMPLE III 
A Lindberg Model 54357 3-zone furnace identical in design and size as that 
of Example I, was also used in this example. The elements were likewise 
given by the same manually set Lindberg Model 59744-A Control Console. The 
ends of the heating chamber were plugged with heat resistant material to 
minimize heat loss from the furnace. The reaction tube was supported by 
two rings of woven asbestos tape. One of the rings was located between 
16-19 cm and the other between 42 and 45 cm along the chamber. This puts 
both rings completely inside the center heating zone, just beside the 
junctions of the center elements with those of the two outer sections. The 
rings were constructed such that the tube was held at an angle. The rings 
also served to insulate the heating zones from each other, by acting as 
barriers to heat transfer. 
The quartz reaction tube was round bottomed, 48 cm long by 2.5 cm in 
diameter, and reduced to a narrow addition tube 10 cm long by 1.0 cm wide. 
Under a dry nitrogen atmosphere, 5.93 g of red phosphorus and 0.50 g of 
potassium were transferred into the tube. The atom ratio of phosphorus to 
metal was 15. The phosphorus was 99.9999% pure. The potassium was 99.95% 
pure. The tube was evacuated to 3.times.10.sup.-4 Torr and sealed by 
fusing the addition tube several cm's from the wider part of the tube such 
that the total length was 51 cm. The sealed tube was placed in the 3-zone 
furnace as described above. The temperature gradient was driven to 
600.degree. C., 465.degree. C. and 350.degree. C. over a period of hours 
and held there for 72 hours. The power to the elements was then shut off 
simultaneously and the furnace allowed to cool to ambient temperatures at 
the inherent cooling rate of the furnace. The tube was cut open under a 
dry nitrogen atmosphere in a glove bag. The products consisted of single 
crystals, polycrystalline films, and amorphous material. 
D. Production of Cylindrical Boules of Amorphous Polyphosphides 
It was evident from the experiments described in section C that to obtain 
large amounts of amorphous material improvements needed to be made in the 
processes already being used. It was recognized that in order to get bulk 
forms of the material, as opposed to thin films, the conditions 
appropriate for growth had to be confined to a smaller space than 
previously allowed. This translated into allowing only the extreme end of 
the tube to be at or below 375.degree. C. or so. This was accomplishable 
in principle by use of the thermal barriers. However, it was also 
recognized that if the conditions for formation of other materials, i.e. 
single crystalline MP.sub.15 or polycrystalline MP.sub.x (x is much 
greater than 15), were also available over a large area of the tube, these 
materials would act as "traps" for vapor species. It was therefore, also 
necessary to discourage the formation of the other materials. This was 
accomplished by raising the center zone temperatures to levels which would 
be too high for formation of polycrystalline or single crystals. The only 
area then where these materials were favored were through the area of the 
thermal barrier, where rapid temperature drops occurred. 
As shown by the following example, and other experiments summarized in 
Table VII below, further improvements in the procedure were worked out. 
The first was the use of Honeywell Model DCP7000 Digital Control 
Programmers to drive the heating elements. This allowed the 
pre-programming of the temperature changes such that reproducible 
treatments could be made from run to run. Both controlled heat-ups and 
cool-downs could be accomplished, eliminating tube failures, and 
production of white phosphorus. The latter often occurred when tubes were 
cooled rapidly and phosphorus vapor condensed as P.sub.4. This was often 
the reason materials appeared reactive. This reactivity could often be 
removed by soaking the materials in solvents which would dissolve away the 
white phosphorus. The second improvement was the routine of applying an 
"inverted gradient" of 300.degree.-490.degree.-500.degree. C. across the 
tube from the metal/phosphorus source to the deposition zones before vapor 
transport, which cleared the deposition zones of materials, which might 
affect nucleation processes. 
By far, the most important improvement, however, was redesigning the 
geometry of the tube. Instead of a long tube of nearly uniform 2.5 cm 
diameter, the body of the tube was shortened to about 30-32 cm and the 10 
mm diameter addition tube 160 (FIG. 2) lengthened and sealed such that 
about 5-7 cm of this tube remained as available space in the interior of 
the tube. When this latter section was placed in zone 3, and the vapor 
transport gradient applied, this section became filled with solid, bulky 
cylinders of increasing length, as the conditions for growth were 
improved. 
EXAMPLE IV 
A Lindberg Model 54357 3-zone furnace, identical in design and size as that 
of Example I was also used in this example. The elements, however, were 
driven by a Honeywell Model DCP-7700 Digital Control Programmer which 
enabled processing to be pre-programmed and carried out in a reproducible 
fashion. 
The ends of the heating chamber were plugged with heat resistant material 
to minimize heat loss from the furnace. The reaction tube was supported by 
two rings of asbestos tape. The rings were constructed such that the tube 
was held at a slight angle. The rings also served to insulate the heating 
zones from each other. 
The quartz reaction tube was round bottomed, 33 cm long by 2.5 cm in 
diameter, and reduced to a narrow addition tube 162, 20 cm long by 1.0 cm 
wide. Under a dry nitrogen atmosphere, 7.92 g of a ball milled charge of 
atom to atom ratio of 15 to 1 was loaded into the tube which was evacuated 
to 1.times.10.sup.-4 Torr and sealed by fusing the addition tube 10 cm 
from the wider part such that the total length was 43 cm long. The sealed 
tube was placed in the 3-zone furnace using the woven barriers described 
above. 
With the tube between 6 and 49 cm, one thermal barrier at 16-19 cm and the 
other at about 38-40 cm, the Honeywell Programmer was used to apply an 
"inverted gradient" of 300.degree., 490.degree., 500.degree. C. for 10 
hours. After the furnace cooled at the inherent rate of the furnace, the 
tube was moved to lie between 12 and 55 cm. The thermal barriers were also 
rearranged to lie at 18.5-21.0 cm and 44.5-47 cm. The programmer then 
drove the gradient to 600.degree., 485.degree., 300.degree. C. for 64 
hours. The programmer then took the tube through a controlled cool-down 
sequence to a 180.degree., 190.degree., 200.degree. C. gradient, which was 
held for 4 hours. The furnace was then allowed to cool to ambient 
temperatures at the inherent cooling rate of the furnace. 
The tube was cut open under a dry nitrogen atmosphere and 4.13 grams of a 
2-3 cm long solid homogeneous amorphous boule recovered from the addition 
tube 162 (FIG. 3). 
The results of several other runs are shown in Table VII. 
TABLE VII 
__________________________________________________________________________ 
Wt. Press.* 
T.sub.1 
T.sub.2 
T.sub.3 
Time 
Tube Yield 
Ref. No. 
Charge 
grams 
Torr .degree.C. 
.degree.C. 
.degree.C. 
Hours 
Length cm 
Amorphous.sup.1 
__________________________________________________________________________ 
20 K/P.sub.15 BM 
6.1 5 .times. 10.sup.-4 
600 
440 
325 72/124 
47.0 not 
determined 
21 K/P.sub.15 BM 
6.05 
6 .times. 10.sup.-4 
600 
460 
300 64/78 
39.0 1.5 cm 
boule 
22 K/P.sub.15 BM 
5.72 
1 .times. 10.sup.-5 
600 
475 
300/200 
64/78 
38.0 1.5 cm 
boule 
23 K/P.sub.15 BM 
5.87 
1 .times. 10.sup.-5 
600 
485 
300/200 
64.78 
40.0 4.0 cm 
boule 
24 K/P.sub.15 BM 
8.05 
5 .times. 10.sup.-5 
600 
485 
300 64 47.0 58% 
25 K/P.sub.7 BM 
7.39 
5 .times. 10.sup.-4 
600 
485 
300 64 44.0 36% 
26 K/P.sub. 15 BM 
7.92 
1 .times. 10.sup.-4 
600 
485 
300 64 43.0 52% 
27 K/P.sub.5 BM 
7.83 
5 .times. 10.sup.-5 
600 
485 
300 104 41.0 12% 
28 K/P.sub.15 BM 
8.0 1 .times. 10.sup.-4 
600 
500 
300 104 43.5 53% 
29 K/P.sub.15 BM.sup.b 
7.95 
1 .times. 10.sup.-5 
600 
485 
300 104 45.5 54% 
30 K/P.sub.35 BM 
7.78 
5 .times. 10.sup.-4 
600 
500 
300 104 35.0 66% 
31 KP.sub.125 CP 
5.40 
5 .times. 10.sup.-4 
600 
500 
300 104 34.5 71% 
32 KP.sub.15 CP 
6.96 
1 .times. 10.sup.-5 
600 
500 
300 104 35.0 51% 
33 Rb/P.sub.15 BM 
7.50 
5 .times. 10.sup.-5 
600 
500 
300 104 45.5 43.0% 
34 RbP.sub.15 CP 
7.19 
1 .times. 10.sup.-5 
600 
500 
300 104 33.5 37.1% 
35 Na/P.sub.15 BM 
8.58 
1 .times. 10.sup.-5 
600 
500 
300 104 34 46.7% 
36 NaP.sub.15 CP 
7.45 
1 .times. 10.sup.-5 
600 
500 
300 104 34.5 53.7% 
37 Cs/P.sub.15 BM 
9.73 
5 .times. 10.sup.-4 
600 
500 
300 104 34.0 15.8% 
__________________________________________________________________________ 
.sup.1 boule length or % of charge 
CP condensed phase product as charge 
BM ball milled product as charge 
*pressure at seal off 
The results showed the yields of material to be fairly independent of the 
charge type--i.e. ball milled, or the pre-reacted condensed phase 
products. However, there was a distinct dependency of yield on the P/M 
ratio. The greater the relative amount of metal in the charge, the lower 
the yield of material. As the amorphous material is essentially 
phosphorus, this reflects a lower vapor pressure of phosphorus over a 
metal-phosphorus charge the greater the metal content; hence, a slower 
rate of growth for identical thermal conditions. 
Table VIII contains some analytical results on amorphous boules prepared. 
It shows potassium content, as determined by wet methods. It also shows 
trace constituents shown to be present by Flame Emission Spectroscopy. 
TABLE VIII 
______________________________________ 
Trace Constituents of MP.sub.x Amorphous Materials 
Constituents Detected by Emission.sup.3 
Ref. K by AA.sup.2 
in ppm at greater than 1 ppm, 
No. Charge.sup.1 
in ppm Values in ppm 
______________________________________ 
21 K/P.sub.15 
427 Fe: .4-4 
K: 20-200 
Si: 6-60 
22 K/P.sub.15 
85 Al: 4-40 
Fe: 6-60 
Si: 20-200 
K: Less than 30 
23 K/P.sub.15 
20-224 As: 2-20 
Si: 1-10 
Did not check for K 
24 K/P.sub.15 
40 Fe: .3-3 
Si: 3-30 
Did not check for K 
25 K/P.sub.7 
285 As: 20-200 
Si: 4-40 
K: 12-120 
Na: 3-30 
26 K/P.sub.15 
161 K: 20-200 
Si: 20-200 
______________________________________ 
.sup.1 Ball Milled only 
.sup.2 Atomic Absorption, on digested sample 
.sup.3 Flame emission spectrographic analysis, on undigested sample 
Tables IX, X and XI are of analytical data obtained by wet methods on 
product from vapor transport synthesis. 
The P/M ratios in the tables are atom ratios unless otherwise noted. 
TABLE IX 
______________________________________ 
SINGLE CRYSTALS (WHISKERS) 
FROM VAPOR TRANSPORT 
Ref. No. Charge P/M Total* 
______________________________________ 
38 K/P.sub.15 19.1 94.5 
6 K/P.sub.15 19.1 98.8 
10 K/P.sub.15 19.1 99.4 
11 K/P.sub.30 16.4 96.1 
17 K/P.sub.5 11.3 97.7 
______________________________________ 
*Analytical mass balance % M + % P detected 
TABLE X 
______________________________________ 
AMORPHOUS MATERIALS FROM VAPOR TRANSPORT 
Ref. No. Charge P/M Total* 
______________________________________ 
39 K/P.sub.15 
2500 W 100.3 
16 K/P.sub.15 
1750 W 99.7 
21 K/P.sub.15 
2300 W 92.8 
22 K/P.sub.15 
12200 W 97.0 
25 K/P.sub.7 3500 W 97.9 
26 K/P.sub.15 
6200 W 97.8 
23 K/P.sub.15 
greater than 
98.2 
4500 W 
24 K/P.sub.15 
7000 W 93.3 
24 K/P.sub.15 
25000 W 99.5 
27 K/P.sub.5 greater than 
99.7 
84000 E 
28 K/P.sub.15 
7800 W 98.2 
82500 E 
29 K/P.sub.15 
25000 E 94.8 
______________________________________ 
W Wet analysis 
E Flame emission spectroscopy 
*Analytical mass balance % M + % P detected 
TABLE XI 
__________________________________________________________________________ 
ANALYSIS OF VAPOR TRANSPORT PRODUCTS 
__________________________________________________________________________ 
HT Films 
Ref. Residue Ring* Whiskers Poly/Films 
Poly/Films 
Amorphous 
No. Charge 
Total 
P/M Total 
P/M Total 
P/M Total 
P/M Total 
P/M Total 
P/M 
__________________________________________________________________________ 
39 K/P.sub.15 100.3 
2500 
38 K/P.sub.15 94.54 
19.09 
98.40 
1170 
2 K/P.sub.125 95.4 
10.4 
6 K/P.sub.15 98.76 
19.10 
10 K/P.sub.15 99.40 
19.07 
9 K/P.sub.30 
92.35 
4.90 
89.56 
12.04 
96.14 
16.35 
100.4 
infinity 
95.69 
infinity 
96.88 
infinity 
17 K/P.sub.5 97.65 
13.1 
100.50 
11.3 99.51 
213 99.71 
358 
99.81 
347 98.97 
193 
16 K/P.sub.15 99.91 
2300 98.20 
54.5 99.71 
1750 
18 K/P.sub.5 97.91 
137.65 
40 K/P.sub.30 100.00 
greater 
100 1800 
than 
7000 
19 K/P.sub.5 
95.00 
2.88 
20 K/P.sub.15 
95.4 
3.17 
94.91 
13.3 97.9 
1250 98.97 
6250 
21 K/P.sub.15 
80.0 
3.67 98.2 
greater 
99 greater 
92.8 
2300 
than than 
2500 2500 
22 k/P.sub.15 
89 3.23 
88.7 
10.92 95.3 
2190 93.1 
2900 97.0 
12200 
25 K/P.sub.7 
91.2 
3.17 96.3 
2000 97.9 
3500 
26 K/P.sub.15 
89.7 
3.01 
76.70 
11.5 95.1 
4000 97.8 
6200 
23 K/P.sub.15 
91.8 
2.80 95.40 
2200 98.2 
4500 
__________________________________________________________________________ 
KP.sub.x 
Ref. Residue Whiskers 
Poly/Films 
Poly/Films 
Amorphous 
No. Charge 
Total 
P/M Total 
P/M Total 
P/M Total 
P/M Total 
P/M Remarks 
__________________________________________________________________________ 
24 K/P.sub.15 93.3 
7000 99.5 
25000 
27 K/P.sub.5 
96.0 
3.28 93.2 
greater 99.7 
greater 
.sup.E 
than than 
9803.sup.E 84,000 
28 K/P.sub.15 
87.7 
3.42 99.5 
greater 98.2 
greater 
.sup.E is greater 
than 
than than 82500 
12500.sup.E 7800 
29 K/P.sub.15 
93.6 
3.48 1250 
98.3 
15000 94.8 .sup.E is greater 
than 
pure 25000 
41 Na/P.sub.15 94.13 
greater 
97.31 
greater 
98.21 
greater 
Na not detected 
than than than 
700 700 700 
98.80 
greater 
97.23 
greater Na not detected 
than than 
700 700 
42 Na/P.sub.15 98.71 
greater 
97.12 
greater 
98.47 
greater 
Na not detected 
than than than 
700 700 700 
43 Na/Rb/P.sub.30 97.6 
1000 97.3 
1330 
Na/Rb 
4.3/1 
Na/Rb 
3.1/1 
44 Rb/P.sub.14 99 1300 
45 Li/P.sub.7 96.86 
1500 
__________________________________________________________________________ 
Total = total percent of metal and phosphorous measured 
Wet analysis unless noted 
.sup.E Metal content measured by flame emission spectroscopy in atomic 
ratio 
*High temperature (HT) films and rings, see FIG. 2 
PREATION OF METAL POLYPHOSPHIDES BY TWO SOURCE TECHNIQUES 
Polyphosphides have been prepared in two fundamentally different types of 
equipment which are both identified herein as Two Source or separated 
source techniques because in both types of equipment, the metal and 
phosphorus are separated and heated independently on either side of a 
deposition zone. All examples have been carried out on the K-P system. 
In the first method, as shown in FIG. 11, the phosphorus and potassium 
charges are held at opposite ends of a sealed quartz tube 100. The tube is 
subjected to a temperature profile as shown in FIG. 12, achieved by use of 
a three zone furnace. The profile takes the independent charges to 
elevated temperatures, relative to the center zone between the two 
constituents. In this zone, the vaporized constituents combine to form the 
deposited product of KP.sub.15, in the form of films on the reactor walls. 
(More complete details appear in Example V below) 
In the second apparatus, as illustrated in FIG. 14, a substantial section 
generally indicated at 102 is at ambient temperature held outside the 
three zone furnace 104. This section includes a stopcock 106 and 
ball-joint 108 arrangement used to achieve the low-pressures desired to 
carryout the reaction. This alternate sealing technique requires lower 
temperatures for this portion of the set up, but allows for rapid and 
nondestructive insertion of a glass "boat" which holds the phosphorus and 
metal sources. The boat 112 (see FIG. 15) also is designed to hold metal 
on glass substrates 114 (FIG. 14) upon which the films are to be 
deposited. These film/substrate configurations serve as initial starting 
points for device designs, as indicated below. 
The section outside the furnace provides a cold trap for vapor species. 
Specifically, phosphorus, which is loaded into the zone closest to the 
outside section, is deposited in the outside section in large amounts, 
generally as the highly pyrophoric white form. Because this trap exists, 
the vapor pressure conditions of the system are quite different from the 
totally-heated systems described above. It follows that the temperature 
conditions which successfully yield desired products in the first 
apparatus, are not appropriate for the second apparatus. The conditions 
appropriate for the latter were independently determined. 
EXAMPLE V 
In the 54 cm long by 2.5 cm diameter quartz tube 100, with a 10 cm long by 
1.0 cm diameter neck 116, shown in FIG. 11, phosphorus and potassium were 
loaded, under dry nitrogen conditions, into opposite ends of the tube, in 
an atom to atom ratio of 15 to 1. The potassium (99.95% pure) was loaded 
first by dropping small pieces, totaling 0.28 g in weight, into a cup 118 
with the tube oriented vertically. The pieces were then melted and allowed 
to resolidify in the cup. The phosphorus (99.9999%) was then added to the 
tube, the 3.33 grams of pieces easily being manipulated around the cup 
118. The tube was then sealed by fusion of the neck 116, at 
5.times.10.sup.-5 Torr. 
The tube was then arranged in a Lindberg Model 54357-S 3-zone furnace to 
lie centered amongst the three zones. Unlike the Model 54357, which has 
zone lengths of 6, 12 and 6 inches (15.2, 30.5, and 15.2 cm), the S model 
has zones of 8, 8 and 8 inches (20.3, 20.3, and 20.3 cm). Two woven 
asbestos tapes, spiraled around the tube, held it at the junctions of 
zones 1 and 2, and zones 2 and 3. Not only did these tapes support the 
tube, they insulated the center zone from the higher temperatures of the 
outside zones. A schematic representation of the resultant temperature 
profile is shown in FIG. 12. A Honeywell Model DCP-7700 Digital Control 
Programmer was used to drive the three heating zones through an 
appropriate warm-up period, to the 450.degree., 300.degree., 450.degree. 
gradient, which was held for 72 hours, and then through a 15 hour cool 
down sequence to ambient temperature. 
The materials formed in the tube were analyzed by the following procedure. 
First, in a dry nitrogen atmosphere, the tube was cut into seven tubular 
sections, of approximately equal lengths, by use of a silicon carbide saw. 
Pieces of the films found in the sections (generally 10 microns or greater 
in thickness), were removed and individually examined by X-ray diffraction 
techniques. The remainder of each section was subjected to analysis by wet 
methods. 
The P/K ratios of the deposits found for the sections are indicated in FIG. 
13. For the center regions, where T was approximately 300.degree. C., the 
bulk compositions were about 14/1, which falls within the accuracy limits 
of the methods employed to identify the material as KP.sub.15. More 
revealing were the X-ray powder diffraction patterns for the materials 
found having a P/K of about 14, which clearly showed they matched those of 
KP.sub.15, either from single whiskers or bulk polycrystalline material. 
Furthermore, the patterns clearly showed the presence of both 
polycrystalline and amorphous materials in about a one to one ratio, as 
manifested by broadening of the peaks. 
EXAMPLE VI 
The apparatus used in this example was modified relative to that of Example 
V. The quartz tube 119 was fabricated with "nozzles" 120 and 122 
segregating the two end chambers from the center one (see FIG. 16). Under 
dry nitrogen conditions, melted potassium (0.47 g, 99.95% purity) was 
added to the outside chamber indicated at K, and allowed to resolidify. 
The addition tube 124 was then fused shut. Phosphorus (5.58 g, 99.9999% 
purity) was then added to the other outside chamber indicated at P and the 
whole apparatus evacuated and sealed at 1.times.10.sup.-5 Torr, by fusion 
of the second addition tube 126. The phosphorus to potassium ratio in the 
system was 15 atoms to 1 atom. 
The sealed tube 119 was 41 cm long, and was centered amongst the three 
consecutive 20.3 cm zones of a Lindberg Model 54357-S 3-zone furnace. Two 
thermal barriers (TB) of woven asbestos tapes, spiraled around the tube, 
held it at the junctions of zones 1 and 2, and zones 2 and 3. In addition 
to holding the tubes, they insulated the center zone from the higher 
temperatures of the outside zones. A Honeywell Model DCP-7700 Digital 
Control Programmer was used to drive the three heating zones through a 
warm up period, to a 500.degree., 355.degree., 700.degree. C. gradient. 
(The phosphorus was at 500.degree. C., the potassium at 700.degree. C. The 
center zone temperature was selected as 300.degree. C., but because the 
insulating characteristics of the woven tape are limited, heat spillover 
from the side chambers raised the center zone temperature to the 
355.degree. C. level.) This gradient was held for 80 hours, and then a 24 
hour cool-down sequence was followed. 
When tube 119 was cut open, under dry nitrogen conditions, using a silicon 
carbide saw, it was found that nozzle 122 between the potassium zone K and 
the center zone had become clogged with material, which looked like 
polyfibrous KP.sub.15. The center zone contained thin, light red films; 
thicker, darker red films; and several, relatively large, monolithic 
boules. The two largest pieces were each about 4 cm long, by 1 cm wide, 
with a maximum thickness of about 4 mm. One side of each piece is 
relatively planar, while the other has a convex configuration, associated 
with growth against the inside walls of the circular reaction tube. 
Wet analysis of this material showed the potassium content to be extremely 
low, as a bulk analysis, at less than 60 parts per million. Electron 
Spectroscopy for Chemical Analysis (ESCA) indicated that the potassium 
content of this material decreased rapidly outwardly of the tube wall on 
which it was first deposited. At 100 angstroms the ratio of P-K was about 
50. As measured by ESCA the P-K ratio on the final surface deposited was 
in the order of 1000. X-ray diffraction studies showed the material to be 
amorphous. 
EXAMPLE VII 
Under dry nitrogen conditions, 0.19 g of melted potassium (99.95% purity) 
were transferred to one of the outermost sections 128 (5 cm long) of a 
pyrex boat 112 (FIG. 15). The metal was allowed to resolidify. Two plain 
glass substrates 114 (see FIG. 14), each about 7.5 cm long by 1 cm wide, 
were laid end to end, filling the 15.3 cm long center section 130. Next, 
1.36 grams of phosphorus (99.999% purity obtained from Johnson Matthey) 
were added to the opposite outside section 132 of the boat. The phosphorus 
is in a mixed-size granular form which readily pours out and fills in the 
bottom of section 132. Pyrex dividers 113 keep the P and K and substrates 
from sliding in the boat 112. The 35 cm long boat 112 was then carefully 
slid into the 60 cm long by 2.5 cm diameter pyrex reaction chamber 134 of 
FIG. 14, until section 128 with the potassium abutted the round bottom, 
closed end of the chamber 136. A Buna-N O-ring, size 124 was then clamped 
into the O-ring joint 102, and the Teflon Stopcock 106 (supplied by 
ChemVac, Inc) screwed down tightly. On a vacuum line, the stopcock 106 was 
reopened and the chamber pumped down to 8.times.10.sup.-4 Torr. The 
stopcock was then re-closed, sealing the reaction chamber. 
The reaction chamber is arranged in a Lindberg Model 54357-S 3-zone 
furnace. As shown in FIG. 14, two woven-glass tapes 137 and 139, spiraled 
around the tube, supported the chamber at the junctions of zones 1 and 2, 
and zones 2 and 3. These tapes forming thermal barriers (TB) were set to 
just lie completely within the center zone. A third spiraled tape 138 was 
used to support and thermally insulate the point where the apparatus exits 
the heating chamber of the furnace. A cylindrical plug 140 of a 
ceramic-like material was used to stem heat loss out of the furnace 
opening at the other end of the chamber. 
This arrangement of the apparatus results in section 128 of the boat 112 
containing the potassium to lie within the third heating zone, section 130 
containing substrates to lie in the center, or second, heating zone and 
section 132 of the boat containing phosphorus to lie in the first heating 
zone. It also results in a large segment of the apparatus being outside 
the furnace, at ambient temperature. 
A Honeywell Model DCP 7700 Digital Control Programmer was used to drive the 
three heating sections through a warmup period in which the temperatures 
were brought to 100.degree., 150.degree., 100.degree. C. in the phosphorus 
zone, the substrate zone, and the potassium zone, respectively. Then, as 
rapidly as possible (approximately 18 minutes) the gradient was driven to 
500.degree., 300.degree., 400.degree. C., where it was held for about 8 
hours. The furnace was then allowed to cool at its inherent rate, to a 
profile of 100.degree., 100.degree., 100.degree. C., which took about 10 
hours. The furnace then was allowed to cool to room temperature. 
The tube 134 was removed from the furnace. The section outside the furnace 
contained deposits of white, yellow, and yellow-red materials, all of 
which were probably phosphorus in varying stages of polymerization. The 
phosphorus heating zone was clear of material, while the potassium zone 
contained a variety of materials, ranging in color from tan, to yellow, to 
orange. 
The latter extended slightly into the center zone, which otherwise was 
covered through one-half of its length, next to the potassium zone, with a 
dark film, which transmitted red light when a source lamp was shone 
through it. The remaining half of the zone was clear of material. The 
apparatus was opened under dry nitrogen conditions, the pyrex boat 112 
withdrawn, and the glass substrates, covered with the red film, removed 
from the boat, and placed in a tightly sealed bottle, for later analysis. 
(When the remainder of the materials were exposed to ambient conditions, 
the phosphorus deposits in the exposed section of tube would generally 
burn vigorously, though those closest to the phosphorus source did not 
exhibit such reactivity. The materials which were in the potassium-source 
section of the apparatus were very reactive when exposed to moisture. They 
generally burned vigorously, apparently by the production of hydrogen via 
reduction of water.) 
The technique was repeated several times. Further examples are noted in 
Table XII. 
TABLE XII 
__________________________________________________________________________ 
TEMPERATURES DEPOSIT 
REF. 
P CENTER 
K TIME 
K P LENGTH 
No. .degree.C. 
.degree.C. 
.degree.C. 
HRS. 
GRAMS 
GRAMS 
SUBSTRATES cm FURNACE 
__________________________________________________________________________ 
46 500 
300 400 
8.0 0.19 1.47 glass 6.5 A 
47 500 
300 400 
8.0 0.19 1.43 glass and 9.0 A 
Ni on glass 
48 500 
300 400 
8.0 0.26 1.62 Ni on glass 
5.0 A 
49 475 
300 375 
8.0 0.27 1.82 glass 1.0 A 
50 500 
300 400 
8.0 0.15 1.66 glass 1.0 B 
51 550 
300 400 
8.0 0.20 1.72 glass 3.0 B 
52 525 
300 400 
8.0 0.21 1.54 glass 6.5 B 
53 525 
300 400 
8.0 0.21 1.56 Ni/Au/Ni 7.0 B 
1000A.degree./700A.degree./500A.degree. 
54 500 
300 400 
8.0 0.20 1.51 Ni/Au/Ni 8.5 A 
1000A.degree./700A.degree./1000A.degree. 
__________________________________________________________________________ 
There exist limiting conditions for the preparation of the dark films which 
transmit red light. If the temperatures in the two source zones are 
dropped slightly, as in run number 49 of Table XII, the amount of material 
formed, as manifested by the length of the deposit, drops dramatically. 
Similarly, subtle differences between the performance characteristics of 
two otherwise identical Model 54357S 3-zone furnaces require that in the 
second furnace (B), the temperature of the phosphorus source be raised to 
higher temperature (see run numbers 50, 51 and 52). Raising the phosphorus 
source temperature to 550.degree. C. gives a good result, raising it to 
525.degree. C. gives a better result. 
Analysis of materials from runs 46, 47 and 48, by Scanning Electron 
Microscope with electron diffraction analysis (SEM-EDAX) methodologies 
revealed the material to be KP.sub.15 films, on the order of 6-7 microns 
in thickness, and to be of an amorphous character, with no discernible 
structure evident in the micrographs. 
SUMMARY OF VAPOR TRANSPORT CONDITIONS 
Processing features for controlling product types are: 
(1) Use of a three zone furnace for more uniform temperature control; (2) 
Extended tube length; (3) Use of thermal barriers for temperature gradient 
control; (4) Use of thermal plugs at ends of oven; and (5) Use of extended 
narrow addition tube to obtain cylindrical boules. 
Ranges of conditions for one source vapor transport are: 
(1) Reaction zone temperatures range from 650.degree.-550.degree. C.; Cold 
zone deposition temperatures range from 450.degree.-300.degree. C. 
(2) Deposition temperature for single crystals of KP.sub.15 were found to 
range plus and minus 25.degree. C. around a center value of 
465.degree.-475.degree. C. 
(3) Deposition temperature for polycrystalline films were found to range 
from about 455.degree. C. down to 375.degree. C. 
(4) Deposition temperature for amorphous forms of the new form of 
phosphorus range from about 375.degree. C. down to at least 300.degree. C. 
(No lower temperatures were investigated to date) 
The conditions for two source vapor transport are for forming bulk 
KP.sub.15 materials are (FIG. 11 apparatus). Phosphorus, temperature at 
450.degree. C., Potassium at 450.degree. C., and deposit zone at 
300.degree. C.; deposits were thick films of mixed polycrystalline and 
amorphous KP.sub.15 ; for bulk amorphous KP.sub.x (x much greater than 15 
the new form of phosphorus, FIG. 16 apparatus): Phosphorus at 500.degree. 
C., Potassium at 700.degree. C. and deposit zone at 355.degree. C. K 
source became plugged, deposit was bulk amorphous KP.sub.x ; for thin 
films of amorphous KP.sub.15 (FIG. 14 apparatus) Phosphorus at 500.degree. 
C., Potassium at 400.degree. C., and substrate at 300.degree. C. 
For thin films of KP.sub.15, the Phosphorus source may be raised to 
525.degree. C. and amorphous KP.sub.15 is still produced. If the 
Phosphorus source temperature is dropped to 475.degree. C., the system 
does not yield KP.sub.15. If the Potassium source temperature is dropped 
to 375.degree. C., the system does not yield KP.sub.15. The substrate 
temperatures may be raised to 315.degree. C. and the system will still 
yield KP.sub.15, but not if they are raised to 325.degree. C. 
PREATION OF POLYCRYSTALLINE METAL POLYPHOSPHIDES IN LARGE AMOUNTS VIA 
"CONDENSED PHASE SYNTHESIS" 
Although not formed in a physical state appropriate to the tapping of their 
useful semiconducting properties, alkali-metal polyphosphides of the type 
MP.sub.15, MP.sub.7, and MP.sub.11, can readily be prepared in gram or 
more quantities by a technique we call "condensed-phase" synthesis. Before 
using this technique, the reactants are generally brought in intimate 
contact by a ball-milling procedure. Decagram or more quantities of the 
elements are loaded in ball-mills, under dry nitrogen conditions, in the 
desired metal to phosphorus, atom to atom ratio, e.g. P/M 15 to 1 for 
MP.sub.15. The sealed mills are then utilized for 40 or more hours to 
reduce the components to a well-mixed, homogeneous, free-flowing powder. 
The mills are generally heated during 20 hours or so of the milling, to 
about 100.degree. C. This is done to increase the fluidity of metal 
component during the milling. 
A portion of the milled mixture, generally 10 grams or more, is transferred 
to a quartz ampoule, under dry nitrogen conditions. The ampoule ranges in 
size from 2.5 cm in diameter by 6.5 cm in length, to 2.5 cm in diameter by 
25 cm in length, depending on the charge size to be processed. The tube is 
sealed at reduced pressure (generally less than 10.sup.-4 Torr). 
The reaction is carried out by subjecting the tube to an ever increasing 
temperature, under isothermal conditions, until the applied temperature 
reaches 500.degree. or 525.degree. C. By isothermal conditions we mean 
that the whole mass of material is always as nearly as practicable at the 
same temperature to prevent vapor transport from hot to cold portions 
which would result in non-uniform products. The highest soaking 
temperature is held for a substantial time, during which a powdery 
polycrystalline or crystalline product is formed. A typical soaking time 
is 72 hours. The longer the reaction, or soaking time, the more 
crystalline the product (as manifested by grain size, sharpness of X-ray 
powder-diffraction lines, etc). The hot tube is also taken through a 
cooling period (more than 10 hours) to ambient temperature. Slow cooling 
is not necessary for the reaction, but prevents tube breakage due to the 
different thermal coefficients of the products and the quartz ampoule. 
Both the heat-up and cool-down periods have been observed to best be 
devised as relatively long (more than 10 hours) with soaking at 
intermediate temperatures (e.g., 200.degree., 300.degree., 400.degree., 
450.degree. C.) for 4-6 hours. Failure to follow these slow heat-ups or 
cool-downs often resulted in explosions of the reaction tubes. However, 
the products of the condensed phase reactions were the same as in slow 
cool down except that a small quantity of residual phosphorus would be 
white rather than red phosphorus. 
EXAMPLE VIII 
19.5 grams of a ball milled mixture of reagent grade phosphorus and 
potassium, in an atom to atom ratio of 15 to 1, was transferred into a 6.5 
cm long by 2.5 cm diameter quartz tube, which tapered to a 8 cm long by 
1.0 cm diameter section. The transfer was carried out under dry nitrogen 
conditions. The tube was sealed at reduced pressure (1.times.10.sup.-4 
Torr) by fusing the narrow section a centimeter or so above the wider part 
of the tube. 
The tube was supported in the center zone of a Lindberg Model 54357 
three-zone furnace by a second quartz tube, or liner, which was, in turn, 
supported in the radial center of the heating chamber by asbestos blocks. 
The 3-zone furnace heating elements were driven by a Honeywell Model 
DCP-7700 Digital Control Programmer which enables processing to be 
preprogrammed and carried out in a reproducible fashion. Using the 
programmer, the reaction tube was subjected to the following temperatures 
for the indicated lengths of time: 100.degree. C., 1 hr; 450.degree. C., 6 
hrs.; 500.degree. C., 18 hrs.; 525.degree. C., 72 hrs.; 300.degree. C., 2 
hrs.; and 200.degree. C., 4 hrs. (When all three zones are controlled at 
the same temperature, the center zone is highly isothermal, with a 
temperature variance of less than 1.degree. C. across the zone). 
After the furnace cooled to ambient temperature, at the inherent 
cooling-rate of the furnace, the reaction tube was removed from the 
furnace. Under dry nitrogen conditions, the quartz ampoule was cut open 
using a silicon-carbide saw, and the dark purple, polycrystalline mass 
removed. A sample of the material was subjected to compositional analysis. 
Wet analysis gave a P/K ratio of about 14.2 to 1, which is accurate to 
about 6% of the theoretical value of 15 to 1. Products from similar runs 
on K/P.sub.15 charges fell in the same range values, as shown in Table 
XIII. 
TABLE XIII 
__________________________________________________________________________ 
CONDENSED PHASE PRODUCTS 
CHARGE TIME AT 
TOTAL 
REF. 
CHARGE PRODUCT TOTAL SIZE HIGHEST 
HIGH T. 
OVEN PRESSURE 
NO. RATIO P/M PRODUCT % 
GRAMS TEMP. .degree.C. 
HRS. TIME HRS. 
TORR** 
__________________________________________________________________________ 
55 K/P.sub.15 
15.3 85.5 5.5 500 120.5 140 1 
.times. 10.sup.-5 
56 K/P.sub.15 
15.5 99.0 21.2 525 305.0 320 5 
.times. 10.sup.-4 
57 K/P.sub.15 
16.2 97.2 9.2 525 266.0 380 5 
.times. 10.sup.-3 
58 K/P.sub.15 (Pure) 
14.0 99.3 8.8 525 216.0 292 5 
.times. 10.sup.-4 
59 K/P.sub.15 
14.2 94.0 19.2 525 72.0 120 1 
.times. 10.sup.-4 
60 K/P.sub.15 
13.6 96.5 17.7 525 72.0 120 1 
.times. 10.sup.-4 
61 K/P.sub.15 
14.7 97.8 16.7 525 72.0 120 6 
.times. 10.sup.-4 
62 Rb/P.sub.15 
14.9 99.8 9.4 525 216.0 292 5 
.times. 10.sup.-4 
63 Rb/P.sub.15 
12.9 97.05 16.1 525 72.0 120 N.D. 
64 Cs/P.sub.15 (Pure) 
15.5 95.5 13.9 500 120.0 390 5 
.times. 10.sup.-4 
65 Cs/P.sub.15 (Pure) 
N.D. N.D. 15.9 500 260.0 710 1 
.times. 10.sup.-5 
66 Na/P.sub.15 
19.2 97.7 9.1 525 216.0 292 5 
.times. 10.sup.-4 
67 Na/P.sub.15 (Pure) 
14.9 92.7 13.5 500 260.0 710 1 
.times. 10.sup.-5 
68 Li/P.sub.15 
16.35 96.9 7.8 525 144.0 240 1 
.times. 10.sup.-4 
69 Rb/P.sub.7 (Pure) 
6.2 96.8 16.3 500 72.0 130 1 
.times. 10.sup.-5 
70 Rb/P.sub.7 (Pure) 
N.D. N.D. 17.2 500 72.0 130 1 
.times. 10.sup.-4 
71 Cs/P.sub.7 (Pure) 
7.1 96.2 18.6 500 72.0 130 1 
.times. 10.sup.-5 
72 Cs/P.sub.7 (Pure) 
N.D. N.D. 7.9 500 172.0 290 1 
.times. 10.sup.-4 
73 Na/P.sub.7 
6.5 93.6 11.5 500 168.0 360 1 
.times. 10.sup.-5 
74 K/P.sub.15 
N.D. N.D. 14.7 525 72.0 120 5 
.times. 10.sup.-4 
75 K/P.sub.15 (Pure) 
N.D. N.D. 16.1 525 144.0 240 1 
.times. 10.sup.-3 
76 K/P.sub.15 
N.D. N.D. 31.9 500 169.0 330 5 .times. 
10.sup.-4 
77 K/P.sub.15 
N.D. N.D. 28.4 525 144.0 240 5 
.times. 10.sup.-4 
78 K/P.sub.15 
N.D. N.D. 36.4 525 144.0 240 1 
.times. 10.sup.-4 
79 K/P.sub.15 
N.D. N.D. 32.1 525 72.0 124 1 
__________________________________________________________________________ 
.times. 10.sup.-5 
*Example 
N.D. Not Determined 
**When tube sealed 
In addition, several samples from different runs were subjected to 
morphological analysis. The XRD powder diffraction patterns for these 
materials were readily matched to those obtained from the single crystal 
KP.sub.15 samples produced by the vapor-transport methods cited elsewhere. 
The methodology was carried over to other metal-phosphorus systems, as is 
indicated in the table. Comparisons of the XRD data of these materials, 
both with each other and that obtained on single crystals established the 
analogous nature of the products, i.e. they all have basically the same 
all parallel pentagonal tubes of covalently bonded phosphorus. 
MILLING METALS WITH RED PHOSPHORUS 
Introduction 
We have utilized ball milling to prepare homogeneous, intimately contacted 
mixtures of red phosphorus with Group 1a and group 5a metals. 
The milled products are relatively air stable and they provide conveniently 
handled starting materials for the previously described condensed phase 
and single source vapor transport techniques. Their stability indicates 
that polyphosphides have formed at least in part during the milling 
process. 
SUMMARY 
The Group 1a metals (with the exception of lithium) have proved to ball 
mill easily with red phosphorus. The facility of milling becomes even more 
pronounced with the lower melting metals, typified by rubidium and cesium. 
A problem arises when the Group 1a M/P ratio is varied from 1/15 down to 
1/7. The increased metal content generally results in severe agglomeration 
of the charge onto the walls of the ball mill. Fortunately, the 
agglomerated products are easily scraped from the mill and crushed through 
a 12 mesh sieve. Lithium and arsenic are somewhat difficult to mill using 
the standard ball milling procedure due to their hardness and higher 
melting points. 
REAGENT PURITY 
The initial experimental work used reagent grade metals and reagent grade 
phosphorus. We now use only high purity metals and electronic grade 
(99.999% and 99.9999% pure) red phosphorus obtained from Johnson Matthey. 
MODE OF MILLING 
A. Standard Ball Milling (Rotation) 
This was originally the method of choice for the alkali M/P systems. 
However, we have used more intensive grinding processes (cryogenic and 
vibratory milling) for the other group 5a metals. 
The stainless steel ball mills were fabricated "in house" and as shown in 
FIG. 17 comprise a cylinder 150 with these dimensions--4.5" O.D..times.6" 
height.times.1/2" wall thickness. The top of the mill is provided with an 
inner flange 151 to accept a Viton O-ring 152. A stainless steel top 154 
is held in place by a bar 155 tightened down with a screw 156. 
One mill has smooth inside walls. The second mill was constructed with 
three baffles welded onto the walls from top to bottom. These act as 
lifters for the balls and reagents and result in more efficient grinding. 
A total of less than 50-60 g reagent charge is desirable. Initial milling 
experiments used 1/4" stainless steel balls; we have since achieved better 
results with a mixture of 1/4" and 1/8" stainless steel balls. 
CRYOGENIC MILLING (-196.degree. C.) 
This was accomplished using the Spex freezer mill (available from Spex 
Industries, Metuchen, N.J.). 
Due to equipment limitations, only small quantities (2-3 g) can be milled 
in a single operation--however, this can be done quickly at liquid 
nitrogen temperatures (in a matter of a few minutes). Thus, this technique 
finds applicability in reducing to powder form, the harder and higher 
melting metals such as lithium and arsenic. These can then be co-ground 
with red phosphorus in the rotating ball mill or vibratory mill. 
VIBRATORY MILLING 
The equipment (Vibratom) is available from TEMA, Inc., Cincinnati, Ohio. 
This is essentially a ball mill, but instead of using a rotating motion, 
circular vibrations are generated--similar to that of a paint shaker. The 
dimensions of the mill are 51/4" O.D..times.3.5" height.times.1/8" wall 
thickness. 
The mill does not contain baffles. We have used this mill for the difficult 
to mill elements such as As. 
TIME OF MILLING 
There has been considerable variation here. Generally, the duration of hot 
milling is not less than 40 hrs. nor more than 100 hrs. To some extent, 
this has been determined by the system being milled. Less time is required 
for the lower melting Cs and Rb systems. 
TEMPERATURE OF MILLING 
This has either been at ambient temperature or the mills have been 
externally heated to approximately 100.degree. C. with a heat lamp. 
Ambient temperatures are suitable for low melting point metals such as Cs 
(28.7.degree. C.) and Rb (38.9.degree. C.). External heat lamp application 
to 75.degree.-100.degree. C. for 3-4 hours was definitely beneficial for 
the Na (97.8.degree. C.) and K (63.7.degree. C.) systems. Heating to 
100.degree. C. was of no value with Li (108.5.degree. C.). We conclude 
that stable products are the result of milling melted alkali metal and 
phosphorus. 
Ball Milling of K/P.sub.15 
EXAMPLE IX (Reference No. 88, Table XIV) 
Under nitrogen in a dry box, an unbaffled stainless steel ball mill 
containing 884 g of 1/4" stainless steel balls was charged with 6.14 g 
(0.157 atom) 99.95% pure K (from United Mineral and Chem. Co.) and 72.95 g 
(2.36 atom) of 99.9999% pure red P (from Johnson Matthey Chemicals). The 
mill was sealed and rotated on a roll station for a total of 71 hours. The 
mill was heated to approximately 100.degree. C. for 4 hours by playing a 
heat lamp on its surface. The mill contents were discharged in the dry box 
to a 12 mesh sieve and pan. No agglomeration of the product was observed. 
The steel balls were separated from the product on the sieve. A total of 
76.4 g of black powder product was obtained. 
Ball Milling of Cs/P.sub.7 
EXAMPLE X (Reference No. 115, Table XIV) 
Under nitrogen in a dry box, a baffled stainless steel ball mill containing 
450 g 1/4" and 450 g 1/8" stainless steel balls was charged with 12.12 g 
(0.0912 atom) of 99.98% pure Cs (from Alfa/Ventron Corp.) and 19.77 g 
(0.638 atom) of 99.999% pure red P (from Johnson Matthey Chemicals). The 
mill was sealed and rotated on a roll station for 46.5 hours at ambient 
temperature. (no external heat source applied). Upon opening the mill in 
the dry box, almost total agglomeration of the product was observed on the 
mill walls. This material was scraped off with a spatula and discharged to 
a 12 mesh sieve and pan. The chunks of product were then crushed through 
the sieve. A total of 27.8 g of product was collected in the pan. 
Table XIV summarizes the results of milling various metals with red 
phosphorus. As previously noted, these materials are surprisingly stable. 
3 TABLE XIV 
MILLING OF METALS WITH RED PHOSPHORUS CHARGE TOTAL REF. *MODE OF 
RATIO WEIGHT AND REAGENT MILLING NO. MILLING (ATOM) REAGENT PURITY 
SUPPLIER TIME (HRS) TEMPERATURE RESULTS 
80 BM (a,e) K/P.sub.125 0.15 g K-reagent grade J. T. Baker 42.0 
ambient 12.6 g powder- 15 g P-reagent grade J. T. Baker no agglomera 
tion 81 BM (a,e) K/P.sub.30 1.00 g K-reagent grade J. T. Baker 50.0 
ambient 22.7 g powder- 23.8 g P-reagent grade J. T. Baker slight 
agglomeration 82 BM (a,e) K/P.sub.15 1.69 g K-reagent grade J. T. Baker 
41.0 ambient 19.7 g powder-no 20 g P-reagent grade J. T. Baker 
agglomeration 83 BM (a,e) K/P.sub.15 4.20 g K-reagent grade J. T. Baker 
94.5 ambient 52.4 g powder-slight 50 g P-reagent grade J. T. Baker 
agglomeration 84 BM (a,e) K/P.sub.15 4.20 g K-reagent grade J. T. Baker 
66.0 98.degree. C.(66 hrs) 49.9 g powder-no 50 g P-reagent grade J. 
T. Baker agglomeration 85 BM (a,e) K/P.sub.15 2.68 g K-99.95% United 
Min.-Chem 94.5 108.degree. C.(3.5 hrs) 28.6 g powder-1.8 g un- 31.8 g 
P-99.9999% Johnson Matthey milled P-no agglomeration 86 BM (a,e) 
K/P.sub.15 4.20 g K-reagent grade J. T. Baker 43.5 75.degree. C.(43.5 
hrs) 52.6 g powder-no 50 g P-reagent grade J. T. Baker agglomeration 
87 BM (a,e) K/P.sub.15 4.20 g K-reagent grade J. T. Baker 88.0 75.degree 
. C.(65.5 hrs) 54.0 g powder-no 50 g P-reagent grade J. T. Baker 
agglomeration 88 BM (a,e) K/P.sub.15 6.14 g K-99.95% United Min-Chem 
71.0 100.degree. C.(4 hrs) 76.4 g powder 72.95 g P-99.9999% Johnson 
Matthey 89 BM (c) K/P.sub.15 6.14 g K-reagent grade J. T. Baker 41.5 
100.degree. C.(3 hrs) 154.8 g powder 72.95 g P-reagent grade J. T. 
Baker (0.43 g unmilled K) 90 BM (c,d) K/P.sub.15 5 g K-reagent grade 
J. T. Baker 46.5 100.degree. 
C.(4 hrs) 63 g powder-no 59.4 g P-reagent grade J. T. Baker 
agglomeration 91 BM (b,e) K/P.sub.11 4.89 g K-99.95% United Min-Chem 
79.0 100.degree. C.(1 hr) 44.6 g powder-no 42.61 g P-about 99.95% 
Atomergics Chemetals agglomeration 92 BM (c,d) K/P.sub.7 5 g K-reagent 
grade J. T. Baker 49.0 100.degree. C.(3 hrs) 30.2 g powder crushed 
27.72 g P-reagent grade J. T. Baker thru 12 mesh sieve- severe 
agglomeration 93 BM (b,d) K/P.sub.7 7 g K-reagent grade J. T. Baker 69.0 
100.degree. C.(3 hrs) 43.7 g agglomeration 38.8 g P-reagent grade J. 
T. Baker 94 BM (b,e) K/P.sub.7 10 g K-reagent grade J. T. Baker 48.5 
100.degree. C.(4 hrs) 62.6 g crushed thru 12 55.45 g P-about 99.95% 
Atomergic mesh sieve-considerable Chemetals agglomeration 95 BM 
(b,d) K/P.sub.7 5.18 g K-99.95% Alfa/Ventron 48.0 100.degree. C.(3 hrs) 
29.7 g crushed thru 28.72 g P-99.999% Johnson Matthey 12 mesh 
sieve-severe agglomeration 96 BM (b,e) K/P.sub.5 8 g K-reagent 
grade J. T. Baker 52.0 100.degree. C.(3 hrs) 36.2 g crushed thru 
31.68 g P-approx. Atomergic 12 mesh sieve-severe 99.95% Chemetals 
agglomeration 97 BM (a,e) K/As.sub.2 /P.sub.13 2.5 g K-reagent grade J. 
T. Baker 66.5 101.degree. C.(66.5 hrs) 36.0 g powder-no 9.58 g 
As-99.9% Alfa/Ventron agglomeration 25.74 g P-reagent grade J. T. 
Baker 98 BM + CM + VM K/As.sub.4 /P.sub.11 3.35 g K-99.95% Alfa/Ventron 
(1) 285 BM 100.degree. C.(2.5 hrs) As did not mill (b,e) (a,e) 25.68 g 
As lump-99.9999 Johnson Matthey (2) 94 VM ambient As still did not mill 
29.19 g P-99.999% Johnson Matthey (3) separated out 4, 2 min. cycles 
As finally divided As & cryomilled at-196.degree. C. (Spex 
Mill)(CM) (4) recombine & ambient no agglomeration ball mill 
50 hrs 99 BM (c,d) K/As.sub.7 /P.sub.7 2.5 g K-reagent grade J. T. Baker 6 
8.5 approx. 100.degree. 
C. powder-no 33.53 g As powder-99.9% Alfa/Ventron (3 hrs) agglomerat 
ion 13.86 g P-reagent grade J. T. Baker 100 BM K/Bi.sub.2 /P.sub.13 
2.16 g K-99.95% Alfa/Ventron 133.0 approx. 46.4 g crushed thru 12 
23.08 g Bi-99.9999% Alfa/Ventron 100.degree. 
C.(3 hrs) mesh sieve-considerable 22.23 g P-99.9999% Johnson Matthey 
agglomeration 101 BM (b,d) K/Sb.sub.2 /P.sub.13 3.18 g K-99.95% 
Alfa/Ventron 115.5 ambient 54.4 g powder-no 19.80 g Sb-99.9999% 
Alfa/Ventron agglomeration-some (-100 mesh) shock sensitivity 
32.74 g P-99.999% Johnson Matthey 102 BM (a,e) Na/P.sub.15 1 g Na-reagen 
t grade J. T. Baker 72.0 106.degree. C.(23 hrs)19.6 g powder (no 20.2 
g P-reagent grade J. T. Baker agglomeration) 103 BM (d) Na/P.sub.15 
1.92 g Na-99.95% Alfa/Ventron 88.0 approx. 100.degree. C. 39.3 g powder 
(no 38.8 g P-99.999% Johnson Matthey (6.5 hrs) agglomeration) 104 BM 
(b) Na/P.sub.11 5.89 g Na-99.95% United Min-Chem 108.5 approx. 100.degree 
. 
C. 91.5 g powder (no 87.28 g P-approx. Atomergic (4 hrs) agglomerati 
on) 99.95% Chemetals 105 BM (b) Na/P.sub.7 6.28 g Na-99.95% United 
Min-Chem 70.0 ambient 63.9 g powder (no 59.21 g P-approx. Atomergic 
agglomeration) 99.95% Chemetals 106 BM (a,e) Li/P.sub.19.05 0.8 g 
Li-99.9% Alfa/Ventron-rod 67.5 approx. 100.degree. C. 52.5 g powder 
(0.17 g 53.56 g P-reagent grade J. T. Baker (67.5 hrs) unmilled Li) 
107 BM (b) Li/P.sub.9.65 1.6 g Li-99.9% Alfa/Ventron- 70.0 ambient 50.36 
g powder (0.44 g (shot) unmilled Li) 49.99 g P-approx. 
Atomergic 99.95% Chemetals 108 BM (a,e) Rb/P.sub.15 5.56 g Rb-99.93% 
Alfa/Ventron 69.0 ambient --powder (no 30.22 g P-reagent grade J. T. 
Baker agglomeration) 109 BM (a,e) Rb/P.sub.15 5.74 g Rb-99.93% 
Alfa/Ventron 115.5 ambient 35.7 g powder (no 31.2 g P-99.999% Johnson 
Matthey agglomeration) 110 BM (b,e) Rb/P.sub.7 11.22 g Rb-99.93% 
Alfa/Ventron 48.0 ambient 36.2 g crushed thru 28.46 g P-99.999% 
Johnson Matthey 12 mesh sieve-almost total agglomeration 111 
BM Cs/P.sub.15 14.47 g Cs-99.98% Alfa/Ventron 47.5 ambient 60.2 g 
crushed thru 12 50.58 g P-99.9999% Johnson Matthey mesh sieve-consid 
erable agglomeration 112 BM (b,d) Cs/P.sub.15 5.82 g Cs-99.98% 
Alfa/Ventron 67.0 ambient 23.76 g powder (no 20.34 g P-99.999% 
Johnson Matthey agglomeration) 113 BM (b,d) Cs/P.sub.7 12.30 g 
Cs-99.98% Alfa/Ventron 48.0 ambient 29.1 g crushed thru 20.06 g 
P-99.999% Johnson Matthey 12 mesh sieve-severe agglomeration 
114 BM (b,d) Cs/P.sub.7 12.36 g Cs-99.98% Alfa/Ventron 88.5 ambient 26.5 
g crushed thru 20.16 g P-99.999% Johnson Matthey 12 mesh sieve-sever 
e agglomeration 115 BM (b,d) Cs/P.sub.7 12.12 g Cs-99.98% 
Alfa/Ventron 46.5 ambient 27.8 g crushed thru 19.77 g P-99.999% 
Johnson Matthey 12 mesh sieve-almost 100% agglomerated 
BM Ball Milling 
CM Cryo Milling 
VM Vibratory Milling 
ANALYSIS OF PRODUCTS 
Table XV summarizes the various MP.sub.x (X=15 and x much greater than 15, 
the new form of phosphorus) materials synthesized from vapor transport 
with one source (1S-VT), from vapor transport with two source (2S-VT), 
condensed phase processes and chemical vapor deposition (CVD). 
TABLE XV 
______________________________________ 
MP.sub.x M = Li, Na, K, Rb, Cs 
X X = 15 X much greater than 15 
______________________________________ 
1S-VT single X X 
crystals 
poly. B, TF 
amorphous B 
2S-VT single 
crystals 
poly. TF TF 
amorphous TF B 
Condensed 
single 
Phase crystals X 
poly. B* 
CVD amorphous TF 
______________________________________ 
X: = crystals/whiskers 
B: = Bulk greater than 10 micrometers thick 
TF: = Thin film less than 10 micrometers thick 
B* = Powder 
The materials obtained from these techniques were crystals or whiskers, 
referred to as X; solid polycrystalline bulk, referred to as B; solid thin 
film, referred to as TF; solid amorphous, referred to as B and TF; and 
bulk powder from condensed phase synthesis referred to as B*. 
The analysis of MP.sub.15 crystalline materials was given above with 
reference to FIGS. 7-10. As indicated in Table XV, the polycrystalline and 
amorphous MP.sub.15 materials have only been produced in the form of thin 
films. 
Polycrystalline bulk and thin films of KP.sub.x (x much greater than 15) 
were obtained by vapor transport (one source and two sources). These 
polycrystalline thin films nucleate on glass substrates (or glass walls) 
and show dense packing of parallel whiskers growing perpendicular to the 
substrate. SEM photomicrographs, FIGS. 18, 19, and 20 of such materials 
show a large physical separation between the KP.sub.x whiskers. 
These polycrystalline thin films are formed at low temperatures from around 
455.degree. C. to 375.degree. C. where the amorphous phase begins to form. 
Analysis on these materials wet chemical, XRD and EDAX consistently show x 
to be much greater than 15 (typically greater than 1000). A typical powder 
XRD diagram fingerprint of crystalline MP.sub.x (x much greater than 15) 
is shown in FIG. 10. 
As indicated in Table XV, amorphous MP.sub.x materials can be formed in 
bulk form (boules) by the vapor transport techniques. These boules are 
formed in the narrow end 160 of tube 32 (FIGS. 1 and 2), the narrow end 
162 of tube 58 of FIG. 3, or as pieces of material in zone 2 of FIG. 16. 
These materials show no x-ray diffraction peaks. 
XRD powder diagrams were used in our study to characterize the degree of 
amorphicity of the materials obtained by these techniques. These amorphous 
MP.sub.x materials where x is much greater than 15 can be cut, lapped and 
polished using conventional semiconductor techniques for wafer processing. 
This is even true of material containing no more than 50 to 500 parts per 
million of M, a new form of phosphorus. 
The resulting high x, KP.sub.x amorphous wafers or substrates were shown to 
have useful semiconductor properties with electro-optical response almost 
identical with whiskers of KP.sub.15. We therefore conclude that the local 
order of all MP.sub.x materials where x=15 or is very much greater than 15 
(when solidified in the presence of alkali metal) exhibit the same local 
order substantially throughout their extent. This local order is the all 
parallel pentagonal phosphorus tubes. 
Amorphous high x, KP.sub.x materials were prepared with mirror finish 
surfaces for electro-optical evaluation. Routine surface preparation of 
these amorphous materials includes several processing steps such as 
cutting, embedding, lapping, polishing, and chemical etching. Surface work 
damage induced during such processing steps are known to affect the 
electro-optical performance of semiconductor materials. Therefore, 
attention was focused on assessing techniques and processing steps leading 
to a "damage free" surface. The following processing steps have been found 
to be suitable for the preparation of high quality mirror finish surfaces. 
Embedded boules of high x, KP.sub.x (about 1 to 2 cm in length) from Table 
VII were cut with a slow speed diamond saw using minimum pressure. Each 
wafer was sliced to a thickness of approximately 1 mm. The wafer was then 
immersed in a bromine/HNO.sub.3 solution. To remove sufficient cutting 
damage the thickness of each wafer was reduced by this chemical etching by 
approximately 50 micrometers. The wafers were then washed and checked for 
inclusions and voids. The high x, KP.sub.x amorphous material appears to 
be void free. 
A standard low temperature wax (melting point about 80.degree. C.) was used 
to mount the high x, KP.sub.x wafers onto a polishing block. The wafers 
were then lapped at 50 rpm at 2 minute intervals individually with a 400 
and 600 SiC grit using distilled water as a lubricant with a 50 g/cm.sup.2 
weight until a smooth surface was achieved. 
The final polishing step was carried out for one hour at 50 rpm with 50 
g/cm.sup.2 weight on a Texmet cloth with 3 micrometers diamond compound 
and lapping oil as extender. This polishing step was followed by an 
additional fifteen minute polishing step at 50 rpm with 50 g/cm.sup.2 
weight on a microcloth with a slurry of 0.05 micrometers of gamma alumina 
suspension in distilled water. All procedures require scrupulous in 
between cleaning steps in a sonic bath with subsequent rinsing and drying. 
Samples prepared by this technique have a high quality mirror finish 
surface. The final polishing step was performed on standard metallographic 
Buehler polishing equipment. 
Chemical etching plays a prominent role in wafer preparation, surface 
treatment, pre-device preparation, metallization and device processing. 
Numerous review articles are available covering the chemistry and the 
practical aspects of etching processes. However, most information on 
specific etchants is widely scattered throughout the scientific 
literature. An attempt was made to bring together essential information 
that should be useful to the selection of an etching process relevant to 
these amorphous high x materials. Special attention was placed on etching 
procedures and processes used for surface preparation. It was found that 
some of the etching solutions and procedures currently used for GaP and 
InP are applicable but with different etching rates. 
The following etching solutions were selected and tested: 
5-10% Br.sub.2 95-90% CH.sub.3 OH for general etching and polishing 
1% Br.sub.2, 99% CH.sub.3 OH for polishing high quality surface 
(approximately 1 micron/minute) 
5% by weight NaOCl solution for chemical polishing 1HCl: 2HNO.sub.3 (1% 
Br.sub.2) for removing work damage after cutting and lapping 
1HCl: 2HNO.sub.3 for removing surface layer. 
Several samples were prepared for optical absorption measurements. The 
above technique was used to slice and polish on both sides amorphous 
wafers of high x material as thin as 0.5 mm. Reference samples of GaP and 
GaAs crystals were also polished on both sides and used to measure the 
band gap by optical absorption. 
Etching techniques were developed to reveal microstructures and to thin 
down small areas to 0.2 mm thick for optical absorption. 
Several etching solutions were selected and tested. The best chemical 
solution was found to be a mixture of 6.0 g potassium hydroxide, 4 g red 
potassium ferric cyanide and 50 ml distilled water at 70.degree. C. 
Application to reveal an etching pattern takes less than 60 seconds. This 
solution is very stable and can be used with reproducible etching rates. 
After embedding, cutting and polishing, several samples of amorphous 
KP.sub.x, (x much greater than 15) from Tables VII and VIII have been 
etched. Typical microstructures were revealed from this chemical etching 
treatment after 30 seconds. 
FIG. 21 is a photomicrograph at 360 magnification of the etching pattern on 
a surface cut perpendicular to the axis of an amorphous boule of high x 
material grown by single source vapor transport (Reference No. 28, Table 
VII) showing honeycomb microstructures with well defined domains a few 
microns in size. These honeycomb microstructures are characteristics for 
an etching pattern on a material having a two dimensional atomic framework 
(such as parallel tubes). 
FIG. 22 is a photomicrograph at 360 magnification of the etching pattern on 
a surface cut perpendicular to the axis of growth of the amorphous high x 
material grown by two source vapor transport in Example VI. FIG. 23 is a 
photomicrograph of the same etched surface as shown in FIG. 22 at 720 
magnification. FIG. 24 is a photomicrograph at 360 magnification of an 
etched surface perpendicular to the surface shown in FIGS. 22 and 23 and 
shows an etching pattern characteristic of tubular packing. 
Thus we conclude from the available evidence that our MP.sub.x materials 
where M is an alkali metal where x is much greater than 15, i.e. where the 
amount of alkali metal is as little as 50 parts per million, all have as 
their local order the pentagonal phosphorus tubes either all parallel (the 
MP.sub.15 form) or double alternating perpendicular layer (monoclinic 
phosphorus). 
ELECTRO-OPTICAL CHARACTERIZATION OF HIGH PHOSPHORUS MATERIALS FROM ONE 
SOURCE VAPOR TRANSPORT 
The electro-optical characterization was carried out on single crystal 
whiskers, on polycrystalline films, and amorphous films and boules. The 
characterization consists of (1) optical measurements on samples with no 
electrical contacts (absorption edge, photoluminescence) (2) electrical 
measurements with simple contacts of linear behavior (conductivity, 
temperature dependent conductivity, photoconductivity, wavelength 
dependence of photoconductivity, conductivity type) (3) electrical 
measurements with non-linear or rectifying contacts with metals which are 
indicative of the semiconducting behavior. 
From the above data we extracted the properties which indicate that all 
materials produced have electrical criteria for useful semiconductors, 
that is, they all have an energy band gap from 1-3 eV; conductivity 
between 10.sup.-5 -10.sup.-12 (ohm-cm).sup.-1 ; a photoconductivity ratio 
from 100 to 10,000, and chemical and physical stability under ambient 
operating conditions. 
Measurements were carried out on the following equipment: 
______________________________________ 
(1) Absorption edge Zeiss 2 beam IR and visible 
spectrometer 
Photoluminescence 
Low temperature (4.degree. K.) cryostat 
and laser excitation 
(2) Conductivity 2 probe and 4 probe measurements 
Temperature Depen- 
from 300.degree. K. to 550.degree. K. in 
dent conductivity 
evacuated chamber 
Photoconductivity 
with light source of 
approximately 100 mW/cm.sup.2 
Wavelength dependent 
Xe lamp light source and mono- 
photoconductivity 
chromator 
Conductivity type 
thermoelectric power measurement 
with hot and cold probes 
(3) wet silver paint was used to provide a temporary 
junction to materials, with a photovoltaic opeln circuit 
of 0.2 V measured under illumination. 
______________________________________ 
Metallic and pressure contacts forming junctions were evaluated for their 
current voltage characteristics on a Tektronix curve tracer. 
Data on samples from the broad class of materials under investigation are 
summarized in Tables XVI, XVII, XVIII and XIX. 
Table XVI summarizes the basic physical, chemical and electro-optical 
properties of the prototype material, namely KP.sub.x, x ranging from 15 
to much greater than 15, in various physical forms and chemical 
composition. 
TABLE XVI 
__________________________________________________________________________ 
Typical data on material obtained by single source vapor transport from 
K/P.sub.15 starting charge 
POLYCRYSTALLINE (KP.sub.x) 
AMORPHOUS (KP.sub.x) 
PROPERTIES SINGLE CRYSTAL (KP.sub.15) 
.sub.x much greater than 15 
.sub.x much greater than 
__________________________________________________________________________ 
15 
Electro-Optical 
Conductivity 
10.sup.-7 -10.sup.-8 
10.sup.-7 -10.sup.-8 
10.sup.-8 
(ohm-cm).sup.-1 
Photoconductivity 
10.sup.2 -10.sup.4 
10.sup.2 10.sup.2 
(Light/Dark) (ratio) 
Photoconductivity 
1.4-1.8eV 1.4-1.8eV 1.4-1.8eV 
Peak at 
Activation Energy 
1.2eV 1.4eV 1.6eV 
(2 Eg) from temp- 
erature dependence 
of conductivity 
Absorption 1.8eV 1.4eV -- 
Edge 
Luminescence, 
1.8eV -- -- 
4.degree. K. 
Luminescence, 
1.7eV 1.7eV 
300.degree. K. 
Type -- n-Type n-Type 
Photovoltaic 
-- 0.2eV -- 
(Open Circuit 
Voltage) 
Thermal 
DTA Sharp endotherm 
630.degree. C.-first heat 
615-first heat 590-first heat 
630.degree. C.-second heat 
590-second heat 
590-second heat 
TGA 450.degree. C. 
-- -- 
Decomposition 
450.degree. C. 
-- -- 
Temperature 
(Mass Spectrometer) 
400.degree. C./3hrs. 
Stable up to 450.degree. C. 
Stable up to 400.degree. C. 
Stable up to 350.degree. C. 
Chemical Reagent 
Room Temp.-3 hrs. 
85% H.sub.3 PO.sub.4,95% H.sub.2 SO.sub.4 
Stable Stable Stable 
50% HF, 37.5% HCl, 
Stable Stable Stable 
50% NaOH 
Boiling H.sub.2 O 1 hr. 
Stable Stable Stable 
__________________________________________________________________________ 
Stablility is based upon visual inspection. 
DTA Differential thermal analysis 
TGA Thermal gravimetric analysis 
Table XVII shows the properties of Group 1a (alkali metal) polyphosphides 
of various compositions and physical form. We observed that the 
electro-optical properties are independent of the metal whether it be Li, 
Na, K, Rb, Cs; physical form--crystal, polycrystal, amorphous (boule or 
film); and chemical composition, x=15 or much greater than 15. 
TABLE XVII 
__________________________________________________________________________ 
Polyphosphide -- structural and eletro-optical properties 
A = pattern similar to KP.sub.15 
B = pattern similar to KP.sub.x where .sub.x is much greater than 15 
X-RAY 
POWDER PHOTO- 
CHEMICAL 
DIFFRACTION 
CONDUCTIVITY 
CONDUCTIVITY 
BANDGAP 
MATERIALS 
ANALYSIS 
PATTERN (OHM-CM).sup.-1 
RATIO (eV) 
__________________________________________________________________________ 
M = K 
crystalline 
KP.sub.15 
A 10.sup.-8 -10.sup.-9 
10.sup.2 -10.sup.3 
1.8 
polycrystalline 
KP.sub.x x &gt;&gt; 15 
B 10.sup.-7 -10.sup.-9 
10.sup.2 1.8-2.0 
amorphous 
KP.sub.x x &gt;&gt; 15 
amorphous 
10.sup.-8 -10.sup.-9 
10.sup.2 1.8-2.0 
M = Na 
crystalline 
NaP.sub.15 
A 10.sup.-8 10.sup.2 1.8 
polycrystalline 
NaP.sub.x x &gt;&gt; 15 
B 10.sup.-7 10.sup.1 -10.sup.2 
1.8 
amorphous 
NaP.sub.x x &gt;&gt; 15 
amorphous 
10.sup.-7 -10.sup.-9 
10.sup.3 1.8 
M = Rb 
crystalline 
RbP.sub.15 
A 10.sup.-7 -10.sup.-8 
10.sup.2 1.8 
polycrystalline 
amorphous 
M = Cs 
crystalline 
CsP.sub.15 
A 10.sup.-8 10.sup.2 1.8 
polycrystalline 
amorphous 
__________________________________________________________________________ 
Table XVIII summarizes the properties of mixed polyphosphides and shows 
those formed of mixed alkali metals have no substantial changes in 
properties; partial substitution of As on P sites is possible and produces 
a reduction in resistivity and possibly in the band gap (i.e. 
substitutional doping). 
TABLE XVIII 
__________________________________________________________________________ 
Mixed Polyphosphides -- electro-optical properties 
CHEMICAL 
X-RAY 
STARTING 
POWDER 
CONDUCTIVITY 
PHOTOCONDUCTIVITY 
BANDCAP 
MATERIAL 
CHARGE PATTERN 
(OHM-CM).sup.-1 
RATIO eV 
__________________________________________________________________________ 
K.sub.y Na.sub.1-y P.sub.x 
crystalline 
K.sub.12 /Na/P.sub.160 
A 10.sup.-8 -10.sup.-9 
10.sup.2 1.8-2 
K.sub.y Li.sub.1-y P.sub.x 
crystalline 
K.sub.6 /Li.sub.2 P.sub.10 
A 10.sup.-9 10.sup.2 1.8 
Na.sub.y Rb.sub.1-y P.sub.x 
crystalline 
Na/Rb/P.sub.30 
A 10.sup.-8 10.sup.2 1.8 
amorphous 
Na/Rb/P.sub.30 
amophous 
10.sup.-9 10.sup.2 1.8-2 
K.sub.y As.sub.z P.sub.x-z 
crystalline 
K/As.sub.2 P.sub.13 
A 10.sup.-9 10.sup. 1.8 
amorphous 
K/As.sub.2 P.sub.13 
amorphous 
10.sup.-7 10.sup.2 approx. 1.6 
K.sub.y As.sub.z P.sub.x-z 
crystalline 
K/As.sub.11 P.sub.4 
A 10.sup.-9 10.sup.2 1.8 
__________________________________________________________________________ 
A = pattern similar to crystalline KP.sub.15 
Table XIX summarizes materials and properties obtained from different 
starting charge ratios. We find that the best properties are obtained with 
materials formed from starting charge proportions of P to K of about 15 
(i.e. between 10 to 30). Below 10 the yield decreases; above 30 the 
physical properties of the amorphous boules begin to deteriorate. 
TABLE XIX 
__________________________________________________________________________ 
KP.sub.x from different starting charges analyzed 
in Tables IX, X, and XI above 
X-RAY PHOTO- 
STARTING 
CHEMICAL 
POWDER 
CONDUCTIVITY 
CONDUCTIVITY 
CHARGE ANALYSIS 
PATTERN 
(ohm-cm).sup.-1 
RATIO 
__________________________________________________________________________ 
K/P.sub.15 reagent 
crystalline 
x = 15 A 10.sup.-8 -10.sup.-9 
10.sup. -10.sup.3 
polycrystalline 
x &gt;&gt; 15 
B 10.sup.-7 -10.sup.-9 
10.sup.2 
amorphous 
x &gt;&gt; 15 
amorphous 
10.sup.-8 -10.sup.-9 
10.sup.2 
K/P.sub.15 pure 
crystalline 
x = 15 A 10.sup.-9 10.sup.2 
polycrystalline 
x &gt;&gt; 15 
B 10.sup.-8 10.sup.2 
amorphous 
x &gt;&gt; 15 
amorphous 
10.sup.-8 10.sup.3 
K/P.sub.30 
crystalline 
x = 15 A 10.sup.-9 10.sup.2 
polycrystalline 
x &gt;&gt; 15 
B 10.sup.-9 10.sup.2 -10.sup.3 
amorphous 
x &gt;&gt; 15 
K/P.sub.5 
crystalline 
x = 15 A 10.sup.-9 10 
polycrystalline 
x &gt;&gt; 15 
B 10.sup.-8 10 
amorphous 
K/P.sub.125 
crystalline 
polycrystalline 
amorphous 
x &gt;&gt; 15 poor physical 
properties 
__________________________________________________________________________ 
A = pattern similar to crystalline KP.sub.15 
B = pattern similar to crystalline KP.sub.x 
We conclude that all these materials in whatever form have a band gap 
between 1 and 3 eV, more particularly in a range from 1.4 to 2.2 eV, since 
1.4 eV is the lowest photoconductivity peak we measured and 2.2 eV is the 
estimated band gap of red phosphorus. The data further indicate that the 
band gap of the best form of these materials is approximately 1.8 eV. 
Furthermore, their surprising high photoconductivity ratios of from 100 to 
10,000 indicate that they are very good semiconductors. 
DOPING 
Bulk amorphous MP.sub.x boules obtained by single source vapor transport 
(Tables VI, VII, X and XI above) in our three zone furnace having a 
composition x much greater than 15 can be processed by cutting, lapping, 
polishing, and etching into high quality, mirror finish wafers of about 
0.5 cm diameter. 
It is on these samples that we have been able to perform electrical 
measurements with different geometrical arrangements of electrical 
contacts to determine accurately the bulk conductivity of the materials. 
By 2 probe and 4 probe measurements, we ascertained the bulk conductivity 
of these materials to be 10.sup.-8 to 10.sup.-9 (ohm-cm).sup.-1. This 
conductivity is too low for the material to be able to form a sharp 
junction with rectifying properties. Therefore, it was our aim to find a 
foreign element (dopant) which would affect the conduction mechanism in 
the material and increase conductivity. As is typical of other amorphous 
semiconductors, the presence of small amounts of impurities in the 
material do not affect the conductivity and, above room temperature, we 
find intrinsic behavior with an activation energy equal to approximately 
half the bandgap, indicative of a midgap Fermi level. The low conductivity 
and large photoconductivity ratio indicate a small number of dangling 
bonds. This indicates that a strong perturbation of the electronic wave 
function of the P-P bond will be required to modify the conductivity and 
conductivity type. 
Two approaches were taken: (1) substitute As or Bi into the P site; (2) 
diffuse a foreign element into the amorphous matrix. 
In the first method K/As.sub.2 /P.sub.13 has As incorporated into the 
matrix. The conductivity is increased by 2 orders of magnitude (Table 
XVIII), and the material remains n type. 
In the second method, after trying many conventional diffusers (e.g. Cu, 
Zn, Al, In, Ga, KI) in vapor, liquid and solid phase diffusion with no 
success, we found a surprising success with the diffusion of Ni and then 
Fe and Cr from the solid phase. For example, a layer of Ni was deposited 
by vacuum evaporation onto a well prepared surface of a high x, KP.sub.x 
wafer. After annealing for several hours, the Ni was found to diffuse for 
about 0.5 micrometers into the substrate and the conductivity increased by 
more than 5 orders of magnitude. The conductivity is still n type. 
More specifically, 1500 angstroms of Ni were deposited onto the wafer in a 
Varian resistance heated vacuum evaporator under pressure of 10.sup.-6 
Torr. The sample was sealed in an evacuated Pyrex tube and heated for 4 
hours at 350.degree. C. The top Ni layer was removed. The conductivity 
measured by the two probe method showed an increase from 10.sup.-8 to 
greater than 10.sup.-4. Electro spectroscopy for chemical analysis (ESCA) 
depth profiling of the sample showed the diffusion depth to be 0.4 
micrometers and the chemical bonding of the Ni to be Ni.degree., i.e. free 
Ni in the material. The wavefunction of the Ni overlaps with electronic 
wavefunctions in the P-P matrix, affecting the conduction (mobility). The 
Ni concentration is greater than about 1 atom percent. 
Evaporated gold top contacts or dry silver paint in coplanar fashion form 
ohmic contacts to the doped layer. 
Variations in the diffusion temperature show 350.degree. C. to be optimum 
for Ni diffusion. 
Variation in the diffusion time follow the diffusion equation (diffusion 
depth is proportional to square root of time) and 1500 angstroms of Ni 
heated at 350.degree. C. for 60 hours, showed diffusion depth of 1.5 
micrometers as measured by ESCA. 350.degree. C. approaches the highest 
temperature these amorphous materials may be subjected to. 
Ni diffusion can also be accomplished from the liquid phase, such as from a 
Ni-Ga melt, or from the vapor phase, such as from Ni carbonyl gas. 
It was further found that Fe and Cr show similar behavior under the above 
processing procedures. 
For example, we took a cut wafer from a bulk amorphous high x boule 
obtained by the single source vapor transport and evaporated 500 angstroms 
of iron onto it and then diffused it into the wafer at 350.degree. C. for 
sixteen hours. Applying two pressure probes to the doped material gave a 
full non-linear characteristic on the Tektronix curve tracer. 
On another wafer of high x material we evaporated 300 angstroms of nickel 
and 200 .ANG. of iron, then heated the wafer to 350.degree. C. for sixteen 
hours. We then evaporated two 1 mm radius aluminum contacts 2000 angstroms 
thick and upon measuring the current voltage characteristic with the 
Tektronix curve tracer between the aluminum dots, again obtained a full 
non-linear characteristic. 
On another wafer of high x material produced by single source vapor 
transport, we evaporated 500 angstroms of nichrome and then heated the 
wafer for diffusion at 350.degree. C. for sixteen hours. We then 
evaporated two aluminum 1 mm radius dots 2000 angstroms thick onto the 
wafer and again measured a full non-linear characteristic between the two 
aluminum dots. 
We thus conclude that nickel, iron and chromium are useful diffusants in 
these materials for lowering conductivity and that on the lower 
conductivity material junctions can be effected with wet silver paint, 
pressure contacts and aluminum contacts. 
Other elements besides Ni, Fe and Cr with occupied d or f outer electronic 
levels that can overlap with the phosphorus levels are expected to be able 
to affect the conductivity in these materials such as to give p-type 
material and form p/n junctions for solid state devices. 
AMORPHOUS HIGH PHOSPHORUS MATERIAL BY TWO SOURCE VAPOR TRANSPORT 
Two types of materials were obtained by this method and the properties of 
these were investigated. 
(1) Amorphous bulk KP.sub.x, (Example VI) where x equals approximately 50 
on one side and x is much greater than 15 on the other. Surface analysis 
supports the hypothesis of the template effect, which is very strong in 
this instance. The surface of a cut and polished sample is of very high 
quality, low number of defects and voids, uniform etching pattern. 
The conductivity measured was by the two probe technique 10.sup.-10 
(ohm-cm).sup.-1 and the photoconductivity ratio under illumination of 100 
mW/cm.sup.2 is greater than 10.sup.3. The photoconductivity peak is 
approximately at 1.8 eV, indicating a bandgap of that order. The data 
indicates that the P-P bond dominates the electrical and optical 
properties of this material as well as those in Tables XVI, XVII, XVIII 
and XIV, and its strong photoconductivity ratio is consistent with a 
highly reduced level of dangling bonds. 
(2) Amorphous thin films of KP.sub.15, (Reference No. 47 Table XII) 
deposited onto glass slides which have a metal layer deposited on them for 
a back contact to the thin film. The success in the thin film deposition 
of KP.sub.15 opens the opportunity to manufacture many types of thin film 
devices. 
The amorphous KP.sub.15 thin films deposited by the 2 source technique have 
a thickness of approximately 0.5 micrometers over an area of 3 cm.sup.2. 
The film is uniform and the surface roughness does not exceed 2,000 
angstroms. The film is chemically stable. FIG. 25 is a photomicrograph at 
2000 magnification of the surface of one of these KP.sub.15 films. The 
adhesion to the substrate is excellent. Quantitative analysis of the film 
was performed using a Scanning Electron Microscope (SEM) and an Energy 
Dispersive X-ray (EDAX) measurement. The composition of the film was found 
to be in agreement with the KP.sub.15 nominal composition. The uniform 
composition, homogeneity, and pinhole free surface leads to uniform 
electro-optical properties across the films. 
In view of the diffusing capability of Ni into bulk amorphous KP.sub.x, an 
Ni film 172 was evaporated onto the glass substrate 170 to form a back 
contact for the amorphous KP.sub.15 layer 174 as shown in FIG. 26. 
The Ni serves as a back contact and a diffuser. ESCA and SEM profiling 
shows Ni to diffuse significantly into the KP.sub.15 film 174 at a rate of 
200 angstroms per hour during the KP.sub.15 growth process. 
In more detail, we deposited by vacuum evaporation 1500 angstroms of Ni 172 
onto a glass slide 170 at 10.sup.-6 Torr. pressure. Part of the Ni surface 
is then masked with a Ta mask in order to have a material free zone for 
electrical contact. 
Two micrometers of amorphous KP.sub.15 174 is deposited in our two source 
apparatus onto the Ni film 172. The composition of this film has been 
identified to be KP.sub.15, it is amorphous and has more than 1% Ni 
diffused into the film. 
Pressure contact with an electrical probe was applied to the top of the 
KP.sub.15 film. The two leads, from the back contact and the top pressure 
contact, were connected to a Tektronix Curve Tracer 176 to observe the 
current voltage characteristics. The forward characteristic of the 
rectifying pressure contact junction is shown in FIG. 27, which indicates 
a junction with a barrier height of 0.5 eV and current in the mA range. 
As shown in FIG. 28, we also deposited by vacuum evaporation a 2 mm radius 
Cu contact 178 onto the top surface 180 of a KP.sub.15 amorphous layer 182 
grown by the two source technique on a Ni layer 184 deposited on a glass 
substrate 186. We connected the Tektronix curve tracer 176, as shown, and 
measured the full forward and reverse biased junction curve shown in FIG. 
29, which thus indicated that Cu forms junctions with these materials. 
Subsequently, smaller metal dots were deposited as top contacts in order to 
reduce the effect of leakage currents at the edges of the contacts. 
10.sup.-3 cm.sup.2 area top contacts and 10.sup.-5 cm.sup.2 top contacts 
were deposited in the vacuum evaporator through mechanical masks. The I-V 
characteristics shown in FIG. 31 were observed with Cu, Au, and Al top 
contacts. They appear as the breakdown voltages of two back to back diodes 
in each instance. Similar curves were obtained with Ni, Ti, Mg, and Ag as 
the top contacts. 
The most significant difference appears in the fact that Au contacts change 
the I-V characteristic after applying 10 V to the device. The I-V 
characteristic become asymmetric, as shown in FIG. 32, and a more ohmic 
contact is formed at the Au interface after this "forming" process. The 
"forming" is consistently observed with Au, and intermittently observed 
with Ag and Cu top contacts. The "forming" does not permanently affect the 
device, but it reappears every time a voltage is applied. Heating the 
device at 300.degree. C. does not affect the phenomenon. Cooling the 
device to -20.degree. C. results in very sharp I-V characteristics (FIG. 
33). 
It appears as if the "forming" may be a breakdown of a high resistance 
layer remaining between the diffused part of the device and the top 
contact. Capacitance--voltage (C-V) characteristics shown in FIGS. 34, 35, 
and 36 point in the same direction. Al and Au top contacts have C-V 
characteristics of double diodes, but convert into single diode behavior 
in the case of Au contacts. If we assume a dielectric constant of 
approximately 10, we can extract a carrier concentration of approximately 
10.sup.16 carriers per cm.sup.3 near the junction and a carrier mobility 
of approximately 10.sup.-2 to 1 cm.sup.2 /volt second. Frequency 
dependence of the capacitance and resistance in FIG. 37 can be used to 
model the multiple junctions that can form in such a structure with a 
graded diffusion profile in the active material. In addition, poor bulk 
material quality (low density) and rough surface morphology could 
contribute to the complex observations. Nonetheless, junction formation 
capability on amorphous two-source thin film KP.sub.15 has been 
demonstrated. 
Some of the above phenomena, such as "forming" with Au top contacts was 
also observed with flash evaporated thin films deposited on Ni. This film 
is not pure KP.sub.15, but has excellent quality. No C-V dependence was 
seen in this case. The device, which was very thin, had a good response to 
light and a small (10.sup.-6 amps) current was drawn from it under short 
circuit conditions when illuminated with visible light. 
We expect that KP.sub.15 thin films made by CVD technique will result in 
similar behavior when the films are sufficiently thick. At the moment they 
have been too thin and have been found to short out. 
The formation of junctions with these materials indicates that they may be 
utilized to form pn junctions, Schottky diodes, or Metal Oxide 
Semiconductor (MOS) devices. 
We expect that by utilizing the above noted classes of dopants, that the 
materials can be converted to p-type conductivity and thus will be useful 
in the entire range of semiconductors. 
The photoconductivity ratio was obtained in all these by forming a 
semiconductor device comprising our material and means attached to the 
material for electrically communicating with it. This means comprised two 
single electrodes 80 and 82 attached to the material, as illustrated in 
FIG. 30. 
More specifically, for a single crystal of MP.sub.15, two copper strips 80 
and 82 were adhesively attached to a glass substrate 84. A sample 86 of 
KP.sub.15, made according to the above teachings, was bridged across 
strips 80 and 82 at one end thereof and attached thereto by silver paint 
88. Meter 90 attached to the opposite ends of strips 80, 82 introduces an 
electrical potential to the KP.sub.15, and thereby permits measurement of 
the resistivity of the KP.sub.15. 
The resultant device of FIG. 30 and similar devices using our other 
materials established that our high phosphorus materials can in fact be 
used to control the flow of electrical current, at least as a 
photosensitive resistor. 
In addition, our materials show luminescence characteristics with an 
emission peak at 1.8 eV at temperatures of four degrees K., and 
luminescence at ambient temperatures. 
PREATION OF LARGE CRYSTAL MONOCLINIC P 
Rubidium 
We have found that the RbP.sub.15 can be utilized to produce large crystal 
monoclinic phosphorus. 
A 0.62 g sample of RbP.sub.15 encapsulated, in vacuo, in a 10 mm 
O.D..times.6 mm I.D..times.5.0 cm quartz tube was vertically positioned in 
a crucible furnace and subjected to a temperature gradient such that the 
RbP.sub.15 charge was maintained at 552.degree. C. while the top of the 
tube was maintained at 539.degree. C. After heating for approximately 22 
hours, the tube was opened and single crystals of monoclinic phosphorus, 
as large as 3.0 mm on edge, in the form of truncated pyramids were found 
in the upper (cooler) region of the tube. 
We found that large crystal monoclinic phosphorus can also be prepared from 
mixtures of Rb and P in the atom ratio of 1 to 15 (RbP.sub.15). 
CESIUM AND SODIUM 
Large single crystals of monoclinic phosphorus were also grown via vapor 
transport using either CsP.sub.15 or NaP.sub.15 charges formed in our 
condensed phase process. In each run approximately 0.5 g of the 
appropriate alkali metal polyphosphide was sealed in vacuo in a quartz 
tube (10 mm O.D..times.6 mm I.D.) of length 8.9 cm. The tubes were then 
subjected to a temperature gradient such that the alkali metal 
polyphosphide charges were maintained at 558.degree. C. while the tops of 
the tubes were maintained at 514.degree. C. After 48 hours, large deep-red 
crystalline stacked square platelets of monoclinic phosphorus formed from 
the CsP.sub.15 charges. 
The morphologies of the monoclinic phosphorus crystals grown from 
CsP.sub.15 and NaP.sub.15 condensed phase charges appear to be very 
similar, that is, stacked square platelets. This is in contrast to the 
truncated pyramidal habit of the monoclinic phosphorus crystals grown from 
a RbP.sub.15 charge. 
We found that large crystal monoclinic phosphorus can also be prepare from 
Cs/P.sub.11, and Cs/P.sub.11 and Cs/P.sub.15 mixtures maintained at high 
temperatures. 
POTASSIUM 
Using similar processes we have also produced monoclinic phosphorus 
crystals from condensed phase KP.sub.15, and from mixtures of K/P.sub.30 
and K/P.sub.125. 
LITHIUM 
No experiments have been conducted with lithium/phosphorus charges. 
However, we expect that large crystal monoclinic phosphorus can be 
prepared from the materials under similar conditions. 
EFFECT OF TEMPERATURE 
While the nature of the alkali metal present seems not to be important, the 
temperature at which the charge is maintained is apparently very important 
to the crystal growth process. In the case of the Cs/P.sub.11 ball milled 
system, large crystals were produced in experiments where the charge was 
maintained at 555.degree. C. and 554.degree. C. However, in experiments 
where the charge was held at 565.degree. C. and 545.degree. C., no large 
monoclinic crystals were produced. 
Referring to FIG. 38, using our preferred apparatus, we sealed a 0.6 gm 
sample of RbP.sub.15 prepared by our condensed phase process in vacuo in a 
12 mm O.D..times.6 mm I.D..times.8 cm long glass tube 270. The top was 
sealed with a 16 mm diameter flat glass surface 272. Fill tube 274 is 
provided with a constriction 276 at which it is sealed after charging and 
evacuation. 
The tube was subjected to a temperature gradient such that the flat surface 
272 at the top of the tube was maintained at 462.degree. C., while the 
charge at the bottom of the tube was maintained at 550.degree. C. After 
heating for 140 hours approximately half of the original charge had been 
transported to the flat surface. 
The resulting button-like boule was cleaved and examined. It was made up 
entirely of uniform light-red fibers--not the desired large crystal 
monoclinic phosphorus. FIGS. 44 and 45 are SEM photomicrographs of this 
product at 200 and 1000x magnification, respectively. 
The SEM photomicrographs of FIGS. 44 and 45 proved to be a surprise. The 
individual "fibers" consist of bundles of long platelets which are 
attached such that they appear to be star-shaped rods when viewed from the 
end. This material is thus quite different in appearance from the "twisted 
tube" fibrous phosphorus produced via vapor transport from a 99.9999% red 
phosphorus charge (see below). 
We conclude that the condensing temperature to form large crystal 
monoclinic phosphorus should be in the range of 500.degree. to 560.degree. 
C. Further experiments indicate that the preferred condensing temperature 
is about 539.degree. C. 
The charge must be heated to a temperature above 545.degree. C. and below 
565.degree. C. as previously indicated. Our preferred range is 550.degree. 
to 560.degree. C. with about 555.degree. C. giving the best results. 
EFFECT OF COMPOSITION 
We have produced monoclinic phosphorus from charge ratios of P to alkali 
metal of 11 to 125. However, a ratio of about 15 seems to work best. 
CHARACTERISTICS OF MONOCLINIC PHOSPHORUS CONDENSED FROM VAPOR IN THE 
PRESENCE OF AN ALKALI METAL 
FIG. 39 is a photomicrograph at 50X magnification showing a pyramidally 
shaped monoclinic crystal of phosphorus prepared from a RbP.sub.15 charge. 
These crystals are hard to cleave. Similar crystals are produced from 
charges utilizing sodium as the alkali metal. We have produced crystals as 
large as 4.times.3.times.2 mm. 
FIG. 40 is a photomicrograph, at 80X magnification, of a crystal of 
monoclinic phosphorus produced from a ball milled mixture of Cs/P.sub.11. 
These platelets are easy to cleave into mica-like sheets. Similar crystals 
can be produced from a charge of K/P.sub.15. We have produced crystals in 
this habit as large as 4 mm on a side and 2 mm thick. 
We have determined that the crystals are birefringent. When placed between 
crossed polarizers in a polarizing microscope, they rotate the light and 
allow some of it to pass through. Thus they may be utilized as 
birefringent devices such as optical rotators in the red and infra-red 
portion of the spectrum. 
Chemical analysis indicates that they contain anywhere from 500 to 2000 
parts per million of an alkali metal. They are made in a process which 
takes as little as 22 hours versus the 11 days employed in the process of 
the prior art to produce Hittorf's phosphorus. 
The powdered X-ray diffraction pattern of these crystals is consistent with 
that of the prior art Hittorf's phosphorus. 
The photoluminescence spectra shown in FIGS. 41 and 42 were taken with an 
Argon laser Raman spectrometer. A broad peak at 1.91 eV is clearly 
observed with a half width of about 0.29 eV. This indicates a band gap of 
about 2.0 eV at room temperature. 
The FIG. 41 spectrum was taken utilizing a monoclinic crystal of phosphorus 
prepared in the presence of cesium, while the FIG. 42 spectrum was taken 
using monoclinic phosphorus condensed in the presence of rubidium. 
The Raman spectrum of FIG. 43 was taken utilizing a monoclinic phosphorus 
crystal formed in the presence of Rubidium. The peaks 280, 282, 283, 284, 
and 285 are at wave numbers 285, 367, 465, 483, and 529. 
Evaporated dots about 25 micrometers in diameter were deposited on large 
crystals of monoclinic phosphorus (from a Rb/P.sub.15 source) for 
electrical measurements. The resistance of the crystals was found to be 
10.sup.6 ohm to 10.sup.7 ohm and practically independent of the geometry 
of the crystal and the size of the contacts. This reflects surface 
resistance. 
These crystals may be utilized as the substrate for depositing 3-5 
materials such as Indium Phosphide or Gallium Phosphide. They may be 
utilized as phosphors in luminescent displays, semiconductors, lasers, and 
as starting materials for other semiconducting devices. 
TWISTED FIBER PHOSPHORUS 
The presence of the alkali metal in the charge appears to be critical to 
the production of large crystal monoclinic phosphorus. We attempted to 
produce large single crystals of monoclinic phosphorus from 99.9999% pure 
red phosphorus by mimicking the conditions used successfully with the 
various alkali metal/phosphorus systems. This attempt failed. No 
monoclinic phosphorus was produced. For example, a 0.6 g sample of 
99.9999% pure red phosphorus was heated at 552.degree. C. in a sealed 
evacuated tube in a vertically positioned 10 mm outside diameter.times.6 
mm inside diameter quartz tube. The temperature gradient between the 
bottom and top of the two and three-quarter inches long tube was 
43.degree. C. After heating for 24 hours, more than half of the charge had 
been transported to the top third of the tube where a boule had formed. 
Surprisingly, the boule was found to consist entirely of a red fibrous 
material. Several long (approximately 1.5 mm) fibers were found in the 
vapor space at the bottom of the boule. Microscopic examination of the 
deep red fibers revealed that they are twisted. 
XRD data secured on the fibrous material were found to match those secured 
earlier on polycrystalline KP.sub.x where x is much greater than 15. FIG. 
46 is an SEM photomicrograph at 500 magnification of these fibers. 
Differential thermal analytical data was found to be similar to that 
secured on polycrystalline high x material. For two DTA determinations, 
the first heat plot consists of a single endotherm at 622.degree. C. 
(average). The second heat plot consists of a single endotherm in both 
cases--at 599.degree. C. The DTA data secured earlier on polycrystalline 
high x material consists of a first heat single endotherm--at 614.degree. 
C. and a second heat single endotherm--at 590.degree. C. Thus, we observed 
substantial similarities between the fibrous phosphorus prepared from 
99.9999% red phosphorus and polycrystalline high x material. 
FLASH EVAPORATION 
We have succeeded in forming stable thin film amorphous coatings on glass 
and nickel coated glass substrates using a flash evaporation process. The 
flash evaporation apparatus is generally indicated at 302 in FIG. 47. It 
comprises a glass cylinder 304 connected to a vacuum system (not shown) 
through tubing 306. Argon is supplied at inlet 308 of supply tube 310. 
Reservoir 312 is filled with powdered KP.sub.15 formed by the Condensed 
Phase method. It is agitated by means of a vibrator generally indicated at 
314 and picked up by the flow of Argon gas through the venturi generally 
indicated at 316. It then flows into the reactor 304, passing through tube 
317 into a steel susceptor 318. The susceptor is heated by means of a RF 
coil 319 to a temperature of at least 900.degree. C., which causes the 
KP.sub.15 to vaporize. At the end of tube 317, as shown in FIG. 49, a 
nozzle is formed by incorporating a plurality of small tubes generally 
indicated at 320 in FIG. 48, having a plurality of small orifices 321. 
Tubes 317 and 320 are alumina and tubes 320 are held within the end of 
tube 317 by means of magnesium oxide cement 322. 
The KP.sub.15 upon vaporization dissociates into its constituents and the 
vapor is carried by the Argon gas through the orifices 321. The film is 
deposited on a cooler substrate 324. The substrate may be heated by means 
of hot wires 326 fed by electrical connections 328. 
Alumina tube 317 has a one-quarter inch outside diameter and one-eighth 
inch inside diameter. Tubes 320 have a one-sixteenth inch outside 
diameter, are one-quarter inch long and have four one-sixteenth inch 
diameter holes through them. 
The apparatus is operated under a vacuum of 0.1 to 0.5 mm Hg. Amorphous 
films of up to 1 micron thick may be formed in runs of up to fifteen 
minutes. At the end of a run, the substrate 324 reaches a temperature of 
200.degree.-300.degree. C., depending on whether it starts out at room 
temperature or is initially preheated to 200.degree. C. 
CHEMICAL VAPOR DEPOSITION 
We have prepared thin films of KP.sub.15 by means of Chemical Vapor 
Deposition. 
A typical chemical vapor deposition reactor is shown in FIG. 50. It is 
constructed of Pyrex. The reactor chamber 401 is a 26 mm I.D..times.27.0 
cm long tube in the center of which is positioned a 6.0 mm I.D..times.30.0 
cm long tube 402 which serves as both a thermowell and substrate holder. 
The thermowell is held in position by an adjustable O-ring collar 403. The 
vent tube 404 allows for the continuous removal of the gaseous exhaust 
stream. It is attached to a trap (not shown) which removes the unreacted 
phosphorus before venting of the stream to air. The vent tube 404 and 
O-ring collar 403 are attached to the reactor chamber 401 through a 2.0 cm 
I.D. O ring joint 405. The reactor chamber 401 is located in a resistance 
furnace generally indicated at 406. 
Molten phosphorus is metered by a piston pump (not shown) through a 1.0 mm 
I.D. capillary tube 407 into a vaporization chamber 408. The molten 
phosphorus is evaporated in the vaporization chamber 408 by a stream of 
argon which is injected into the vaporization chamber 408 through the 6.0 
mm I.D. inlet tube 409. The gaseous phosphorus/argon stream enters the 
reactor chamber through nozzle 410. The nozzle 410 has an opening of 4.0 
mm. The evaporation chamber 408 is located in a resistance oven generally 
indicated at 411. 
A gaseous mixture of potassium and argon is metered into the reactor 
chamber 401 through inlet tube 412 which has a 6.0 mm I.D. Neat argon, 
which acts as a shroud for the potassium/argon stream, enters the system 
through 6.0 mm I.D. tube 413. Both the potassium/argon stream and neat 
argon stream enter the reaction chamber 401 at 414. The potassium/argon 
and neat argon lines (412, 413) are located in a resistance oven generally 
indicated at 415. 
The substrate 416 is positioned on the thermowell 402. The temperature of 
the substrate 416 is determined by a thermocouple 417 positioned directly 
below the substrate 416 on the thermowell 402. 
During operation, ovens 406, 411, and 415 are maintained at appropriate 
temperatures. The gaseous reactant streams enter the reactor chamber at 
410 and 414. The exhaust gas mixture leaves the reaction chamber through 
the vent tube 404. The desired film forms on the substrate 416. 
The substrates are maintained at a temperature of 310.degree.-350.degree. 
C., the temperature being maintained constant to plus or minus 2.degree. 
C. 
In a typical run 1.24 g of white phosphorus and 0.13 g of potassium are 
delivered into the reactor over a two hour period. The total Argon flow 
rate is maintained at 250 ml per minute during the run. 
A number of experiments were conducted in which phosphorus/argon and 
potassium/argon were fed simultaneously into the reactor. The 
phosphorus/argon stream was maintained at approximately 290.degree. C. and 
the potassium/argon stream at approximately 410.degree. C. The calculated 
atom ratio of reactants in the reactor was P/K approximately 15. The 
reactor was maintained at 300.degree.-310.degree. C. In a typical 
experiment the liquid phosphorus feed rate was 0.34 ml per hour. 
Amorphous KP.sub.15 films were prepared using nickel-on-glass substrates. 
The films are about 0.3 millimeters thick. 
With a run time of 1.0 hour, the films produced were found to have nominal 
KP.sub.15 composition. The thickness of the film was dependent on the 
position of the particular substrate in the reactor. Examination of the 
films using SEM showed them to be quite uniform. 
PURIFICATION OF PHOSPHORUS 
50 grams of Atomergic phosphorus, "99.95% pure", was subjected to a 
450.degree.-300.degree. C. gradient for 75 days. After this admittedly 
very long time, 21% of the material remained behind and 60% of the charge 
ended up as amorphous, bulk deposits. 
Previous analysis showed the Atomergic phosphorus to be less than 99.90% 
pure, probably closer to 99.80%, with aluminum, calcium, iron, magnesium, 
sodium, and silicon as major impurities (all greater than 0.01%, and some 
greater than 0.05%). This material costs about $220 per kilogram. In 
comparison, "99%" P from Alpha Ventron is $17/lb., or $37.5/Kilo. 
Table XX summarizes the results of flame emission spectroscopy on three 
materials generated by the aforementioned treatment. 
TABLE XX 
______________________________________ 
IMPURITY LEVELS BY FES* 
Atomergic Material Material 
Material 
Element "99.95" A B C 
______________________________________ 
Al 0.03-0.3% 0.02-0.2% 20-200 less than 1 
Ba 3-60 40-400 2-20 
Ca 30-600 6-60 3-30 less than 2 
Cu .4-4 20-200 less than 1 
less than 1 
Fe 40-400 0.03-0.3% 4-40 less than 1 
Pb .6-6 3-30 
Mg 0.01-.1% 6-60 3-30 less than 1 
Mn 6-60 3-30 less than 2 
Mb .6-6 
Ni 3-30 
Na 0.4-4% MC 30-300 less than 20 
Si 0.04-0.4% 0.3-3% 0.02-0.2% 
less than 1 
Sn 6-60 MC 3-30 
Ti 1-10 1-10 
V 0.6-6 
______________________________________ 
*Flame Emission Spectroscopy 
All values in ppm, except where noted 
0.1% = 1000ppm 
MC = major component measured at greater than 1% 
Material A was a residue, dark brown in color, throughout the charge zone, 
which did not undergo vapor transport. Material designated Material B was 
a hard boule of material, light in color, which did not vaporize, 
primarily because its position in the charge zone results in it being at a 
slightly lower temperature than 450.degree. C. Material C was an amorphous 
boule in the cold zone. 
Clearly, most of the impurities of the charge remain in Material A at 
fairly concentrated amounts. The high impurity levels would be expected to 
give rise to a lower vapor pressure of phosphorus at a given temperature. 
The impurity level of the material pretty well reflects the values for the 
initial charge material. The boule, Material C, is a pretty pure material, 
with the sodium content being the major observed contaminant. Taking the 
sum of contaminants, at their maximum indicated levels, this material has 
a purity level of 99.997%, at worst. The comparable material, obtainable 
from commercial sources, as 99.999% P, costs about $1,800/kilogram. 
Clearly, we have illustrated a cost effective method for purifying red 
phosphorus to a high degree. 
REINFORCED MATERIALS 
The use of phosphorus compounds as fire retardant additives is well known. 
Because of the highly stable nature of the alkali metal containing 
phosphorus materials disclosed herein, they may be utilized for such 
purposes. 
The fibrous and plate-like forms of the materials disclosed herein, for 
example, fibrous KP.sub.15 and KP.sub.x where x is much greater than 15, 
the plate-like monoclinic phosphorus habit, the twisted tube form of 
phosphorus, and the star-shaped material of FIGS. 44 and 45, all show 
promise as reinforcing additives for plastics and glass. The twisted tube 
fibers and star-shaped fibers should be of particular value due to their 
ability to mechanically interlock with the matrix of a composite material. 
Their fire retardant qualities should also prove useful in such materials. 
COATINGS 
As previously discussed, many of the materials disclosed herein form high 
stable amorphous coatings, with good adhesion to metal and glass. The 
MP.sub.15 amorphous films are particularly stable and provide good 
adhesion to metal and glass. Thus they may be utilized as corrosion 
inhibiting coatings on metals and as optical coatings on glass. 
A coating of approximately 1000 angstroms on an appropriate infrared 
optical component such as germanium, will provide a window transparent to 
infrared but showing absorption in the visible. Such coatings when 
combined with coatings of other materials of differing optical index, can 
be utilized to provide anti-reflection coatings on infrared optics. 
Our experiments show that MP.sub.x material can be deposited as films with 
good adhesion on steel, aluminum, and molybdenum. The films are ductile, 
non-porous, polymeric, and non-brittle. 
Thus the materials shown herein should find wide application as coatings 
and thin films. 
INDUSTRIAL APPLICATION 
Thus we have disclosed an entirely new class of high phosphorus 
semiconductor materials. These semiconductors comprise catenated covalent 
atoms where the catenated covalent bonds serve as the primary conduction 
paths in the materials. The catenated atoms form parallel columns as the 
predominant local order. Preferably the atoms are trivalent and have 
bonding angles that permit tubular, spiral or channel-like columns. The 
columns may be joined by atoms of one or more different elements bonded to 
two or more of the catenated columns. 
We have disclosed in particular high phosphorus and mixed pnictide 
semiconductor materials of this class. These include high phosphorus 
polyphosphides of the formula MP.sub.x where x ranges from 7 to 15 and 
entirely new materials where x is very much greater than 15--for all 
practical purposes pure phosphorus. 
These materials can be characterized as containing groups of seven or more 
atoms organized into pentagonal tubes. They may be characterized as having 
the formula MP.sub.x where x is greater than 6 and they may be 
characterized as comprised of phosphorus in a molar ratio of phosphorus to 
any other atomic constituent greater than 6; they may be characterized as 
high phosphorus materials where the phosphorus atoms thereof in 
substantially all local orders comprise phosphorus atoms joined together 
by multiple covalent p-p bonds organized into layers of all parallel 
pentagonal tubes. They may be characterized as polyphosphides containing 
alkali metal atoms wherein the number of consecutive covalent 
phosphorus-to-phosphorus bonds is sufficiently greater than the number of 
non-phosphorus-to-phosphorus bonds to render the material semiconducting. 
They may be characterized as having a skeleton of at least seven 
covalently bonded phosphorus atoms having associated therewith at least 
one alkali metal atom, conductively bridging the phosphorus skeleton of 
one unit with the phosphorus skeleton of another unit; they may be 
characterized as a polyphosphide having the formula MP.sub.x where M is an 
alkali metal and x is at least 7. 
These materials may be further characterized by having a band gap greater 
than 1 eV, that is, from 1.4 to 2.2 eV, and for the best materials we have 
discovered, approximately 1.8 eV. They may be characterized by having a 
photoconductivity ratio greater than 5; more particularly, within the 
range of 100 and 10,000. 
These materials may be further characterized by their trivalent dominant 
atomic species; the homatomic bonds formed by the dominant species; the 
covalent nature of these bonds; the materials' coordination number of 
slightly less than 3; the materials' polymer nature; their formation in 
the presence of an alkali metal or metals mimicking the bonding of alkali 
metals with the dominant species; in the crystalline form, their 
pentagonal parallel tubes either all parallel in KP.sub.15 -like 
materials, paired parallel crossed layers in monoclinic phosphorus, or all 
parallel twisted tubes in twisted fiber phosphorus; their ability to form 
amorphous films and boules retaining their electronic qualities; and by 
their methods of manufacture; and other qualities made apparent in the 
preceding description. 
The amorphous materials we have discovered maintain the electronic 
qualities of the KP.sub.15 all parallel pentagonal tube structure and in 
theory, at least, it appears that that structure is maintained in the 
local scale in our amorphous materials. However, we do not wish to be 
bound by any particular theory in this matter. In particular, the claims 
appearing below should be interpreted broadly to cover all aspects of our 
invention, regardless of later acquired knowledge that might be said to 
conflict with the theories and hypothesis we have put forth, both 
explicitly and implicitly. 
We have disclosed junction devices, photoconductive (resistive) devices, 
photovoltaic devices and phosphors made from these materials. 
We have disclosed resistance lowering dopants, namely Nickel, Chromium and 
Iron, leading to the conclusion that substantially the entire group of 
atomic species having occupied d or f outer electronic levels may be 
utilized if of the appropriate atomic size. 
We have disclosed resistance lowering substitutional doping with Arsenic 
which indicates that all Group 5a metals may be utilized. 
We have disclosed junction devices having a back contact of Ni, Ni diffused 
therefrom, and top contacts of Cu, Al, Mg, Ni, Au, Ag, and Ti. 
We have disclosed new forms of phosphorus wherein the local orders are all 
substantially parallel pentagonal tubes, twisted fiber phosphorus and 
monoclinic phosphorus. We have formed these new forms of phosphorus by 
vapor deposition. The all parallel and monoclinic form require the 
presence of an alkali metal during deposition. 
We have disclosed both amorphous and polycrystalline films of MP.sub.15 
where M is an alkali metal. We have constructed various semiconductor 
devices from all of the all parallel pentagonal tube materials, including 
wafers of MP.sub.x where x is much greater than 15, including a new form 
of phosphorus, amorphous thin films of KP.sub.15 and amorphous thin films 
of KP.sub.x. 
We have disclosed methods of making metal polyphosphides and two new forms 
of phosphorus by controlled two temperature single source techniques. 
We have disclosed methods of making our high phosphorus materials by two 
source vapor transport. 
We have disclosed a method of making high purity phosphorus. 
We have disclosed methods of making crystalline and amorphous forms of 
MP.sub.x where x ranges from 7 to 15 by condensed phase methods. 
We have disclosed chemical vapor deposition, flash evaporation and 
molecular flow deposition methods. 
Industrial applications of the semiconductor materials and devices we have 
discovered are manifest, running the whole gamut of semiconductor 
applications. The crystalline materials may be used as reinforcing fibers 
and flakes for plastics, glasses and other materials. The materials of our 
invention may be used as coatings on metals, glass, and other materials. 
The coatings may protect a substrate from fire, oxidation, or chemical 
attack. The coatings may be employed for their infrared transmitting, 
visable light absorbing qualities. They may be employed with other 
materials as antireflection coatings on infrared optics. The materials may 
be used as fire retardant fillers and coatings. Monoclinic phosphorus may 
be used an an optical rotator. 
It will thus be seen that the objects set forth above among those made 
apparent from the preceding description are efficiently attained and that 
certain changes may be made in carrying out the above methods, processes 
and in the above articles, apparatus and products without departing from 
the scope of the invention. It is intended that all matter contained in 
the above description shall be interpreted as illustrative and not in a 
limiting sense. 
It should be understood that we have used crystalline to mean single 
crystals or polycrystalline material unless otherwise stated. Amorphous as 
distinct from single crystal or polycrystalline, means amorphous to X-ray 
diffraction. All periodic table references are to the table printed on the 
inside front cover of the 60th edition of the Handbook of Chemistry and 
Physics published by the CRC Press Inc., Boca Raton, Fla. Alkali metals 
are identified thereon and herein in Group 1a and pnictides in Group 5a. 
All ranges stated herein are inclusive of their limits. 
By semiconductor device we mean any device or apparatus utilizing a 
semiconductor material. In particular, semiconductor device includes 
Xerographic surfaces and phosphors regardless of how they are excited, as 
well as photoconductors, photovoltaics, junctions, transistors, integrated 
circuits and the like. 
It is also to be understood that the following claims are intended to cover 
all of the generic and specific features of the invention and discovery 
herein described and all statements of the scope thereof which as a matter 
of language might be said to fall therebetween. 
Particularly it is to be understood that in said claims, ingredients or 
compounds recited in the singular are intended to include compatible 
mixtures of such ingredients whenever the sense permits.