AMORPHOUS SEMICONDUCTOR METHOD AND DEVICES

Abstract: Amorphous semiconductors produced to form a wide variety of semiconductor devices, including photovoltaic devices suitable for solar energy conversion. Films produced by the invention have higher relative quantum efficiencies and sensitivities extending to a greater range of wavelengths than films of the prior art. According to the process of the invention, reactants, including the selected polysilanes, are applied to a reaction chamber (260) in the form of an envelope (261). The reaction chamber (260) contains a substrate (262) upon which amorphous silicon is to be deposited. The reaction chamber (261) has an inlet (263) and an outlet (264). The inlet provides entry for selected polysilanes or a monosilane-polysilane mixture through a control valve (251) which allows the gaseous mixture to be supplemented by one of more dopant gases from sources (252) and (255). Positioned below the inlet (263) is a support (265) for a holder (266) of the substrate (262). The substrate holder (266) is a cartridge heater with a wound ceramic core and a ceramic binder encompassing a resistive element (266r). A manometer (270) is mounted on the chamber (261) to give an indication of the internal pressure. The temperature of the substrate (262) is monitored by a gauge (not shown) included in the wiring for the heater (266r). The substrate (262) is typically of glass. In order to make the desired amorphous silicon deposit, the gaseous mixture G is passed over the substrate, being drawn toward the outlet (264) by the effect of a vacuum pump (not shown). The substrate (262) is operated at a temperature in the range from about 350`C. to about 500`C. resulting in pyrolytic decomposition of at least a portion of the gaseous stream G. The decomposition components are indicated by the arrows B shown in dashed line form. The balance of the gaseous mixture, in the form of an exhaust E is drawn through the outlet (264).

Description: 1 AMORPHOUS SEMICONDUCTOR METHOD AND DEVICES Background of the Invention This invention relates to the production of amorphou semiconductors, particularly for use in semiconductor device This is a continuation-in-part of U.S. Serial No. 242,707, filed March 11, 1981. Amorphous semiconductors are useful in a wide variet of devices. Examples include memories, field effect and thin film devices, displays and luminescent devices. 0 Amorphous semiconductors are particularly useful for photovoltaic devices which provide a voltage when subjected to radiation, or radiate when electrically energized. Un¬ fortunately, photovoltaic devices are not presently competi¬ tive with conventional sources of electrical energy. This 5has been caused primarily by the cost of manufacturing suit¬ able semiconductive materials. Initially, expensive and relatively thick single crystal material was required. More recently, amorphous material with suitable photosensitivity has been fabricated by glow discharge in a gaseous atmospher 0 Amorphous material in the form of hydrogenated silico prepared by glow discharge has proved to be particularly suitable. Illustrations are found in U.S. patents 4,064,521 4,142,195; 4,163,677; 4,196,438; 4,200,473 and 4,162,505. Although the glow discharge manufacture of amorphous silicon is less costly than the production of single crys¬ tal material, cost considerations continue to limit the general employment of this technique. One attempt to provide a lower cost material has involved the production of amorphous silicon by pyrolytic decomposition of monosilane (SiH.) . Other techniques employed with monosilanes have included sputtering and vac¬ uum evaporation. Unfortunately, the amorphous silicon produced by the pyrolytic decomposition of monosilane, commonly known as "chemical vapor deposition" (CVD) has shown limited photo- voltaid or photoconductive behavior- This has continued to 3 ~ ~ ~ ~ ~ ' ~ '~ regarded as a defect density in the material. Similarly, amorphous silicons prepared by sputtering and vacuum evaporation of monosilanes have exhibited less photores- ponse than that provided by glow discharge materials. Other attempts have been made to produce amorphous silic from various fluorosilanes as described, for example, in U.S. patents 3,120,451 and 4,125,643. Eere again, while the photore ponsive properties of the resultant materials have been similar to those associated with hydrogenated amorphous silicon produce by glow discharge, the costs of the process are still considera Another method of preparing amorphous silicon is by the decomposition of silanes at a comparatively high temperature {1 to 1600°c.) in a high vacuum reactor required to be held at pre sures below 10 -4 Torr. The resulting gas stream is then direct onto a substrate held at a lower temperature as se * t forth in U. patents 4,237,150 and 4,237,151. This technique is cumbersome, requires the use of high temperatures and high vacuums, and lea to films of rather low photoconductivities (10 —7 (Λ- cm)—1 or lower) . Accordingly, it is an object of the invention to achieve the efficient and low cost production of semiconductive materia with suitable photoresponsive properties. A related object is to achieve suitable photovoltaic and photodetecting devices. Another object of the invention is to provide for the pr duction of semiconductive material with suitable photosensitivi with less cost and complexity than for single cyrs al materials A further object of the invention is to achieve amorphou silicon material at less cost and with less complexity than for glow discharge, sputtering and vacuum evaporation -techniques. Summary of the Invention In accomplishing the foregoing and related objects, the invention provides a method of preparing an amorphous semiconductor with suitable photosensitivity by the pyrolytic decomposition of one or more gaseous phase polysemiconduc- tanes at a temperature below about 500°C. This technique distinguishes from the prior art pyrolytic decomposition of silanes and fluorsilanes in which significantly lower photo¬ conductivity and inferior photovoltaic properties have re- suited. This procedure lends itself to continuous processing as opposed to batch processing, and eliminates the costly and complex equipment associated with the production of single crystal and amorphous silicon by glow discharge, sputtering and vacuum evaporation. In accordance with one aspect of the invention, the decomposition takes place at a temperature in the range about about 300°C. to 500°C. and is preferably in the range from 350°C. to 450°C. In accordance with another aspect of the invention, the decomposition takes place at a partial pressure of poly- silane less than about one atmosphere and above about one micron of mercury, and is preferably above one Torr. The * pressure is desirably in the range from about one Torr to about 100 Torr in order to limit gas phase nucleation of particles during pyrolytic decomposition. ' In accordance with a further aspect of the invention, the polysemiconductances are selected from the class ranging from disemiconductanes to and including hexasemiconductanes, re-presented by the formula ScnH Δ-Xi-r.Z«, where "Sc" refers to a semiconductor such as silicon or germanium, and n ranges from two to six. The polysemiconductanes are desirably obtained from the reaction product of a semiconductide, such as magnesium suicide (Mg-Si) with an aqueous acid such as phosphorus acid (H^PO^) , aqueous strong sulfuric acid (H_S0 4 ) hydrogen fluoride (HF) , and hydrogen chloride (HC1) . The SUBSTITUTE SHEET semiconductanes of an order higher than'disemiconductanes are separated by multiple trap distillation. If higher purity disilane is desired, the disilane that has been trapped may be further purified by multiple traps to trap distillations, by lower temperature, by low temperature fractionation, or by other procedures such as gas chromotography, etc. The polysemiconductanes may also be prepared by reduc¬ tion of semiconductor halides, such as disilicon hexachloride with a hydride such as lithium aluminum hydride. In accordance with a still further aspect of the inven¬ tion, the gaseous phase includes an inert gas carrier. Suit¬ able inert gas carriers are argon, helium and hydrogen. The gas phase material is advantageously decomposed on a heated substrate and the decomposition temperature is that of the substrate. • In accordance with still another aspect of the inven¬ tion, amorphous semiconductive devices are prepared by form¬ ing a body through the pyrolytic decomposition of one or more gaseous phase polysemiconductanes and providing con- tacts for the body. The body is desirably formed on a sub¬ strate in one or more separate layers which can include dopants according to the conductivity type desired. Auxi- ' liary layers, such as metal to form an interface, and anti- reflection layers, can be included. -m-msTl t u n.. Ξr_j_____.T < g! j _t OM Description of the Drawings Other aspect of the invention will become apparent after considering several illustrative embodiments, taken in conjunction with the drawings, in which: FIGURE 1A is a flow chart of the method in accordance with the invention for preparing amorphous semiconductors; FIGURE IB is an adaptation of the flow chart of FIGURE 1A showing the method of preparing amorphous silicons; FIGURE 2A is a schematic diagram of an illustrative arrangement for the production of suitable semiconductanes; . FIGURE 2B is a schematic diagram of an illustrative reaction chamber for preparing amorphous semiconductors in accordance with the invention: FIGURE 2C is a graph of relative quantum efficiency against wavelength illustrating the difference between film produced i in accordance with the invention and those pro¬ duced by other techniques; FIGURE 3 is a schematic diagram of a photodetector prepared in accordance with the invention and associated circuitry; FIGURE 4 is a schematic diagram of a heterojunction semiconductor in accordance with the invention; FIGURE 5 is a cross sectional view of a Schottky barrier photovoltaic device prepared in accordance with the invention; FIGURE 6 is a cross sectional view of a P-I-N photo¬ voltaic device prepared in accordance with the invention; FIGURE 7 is a cross sectional view of a P-N photo¬ voltaic device prepared in accordance with the invention; and FIGURE 8 is a cross sectional view of a further heterojunction photovoltaic device prepared in accordance with the invention. ^-Tz OMPI Detailed Description of the Method With reference to the drawings, FIGURE 1A sets forth a flow charge 100A for the general practice of the invention, while FIGURE IB provides a flow chart 100B for the particu- lar preparation of amorphous silicons having the special properties in accordance with the invention. Semiconductanes for the practice of the invention are selected from Group IV of the Periodic Chart and thus can include germanium or tin, and from Group VI of the Periodic Chart and thus can include selenium and tellurium. As noted below, a particularly suitable semiconductor is silicon. Once the polysemiconductanes are prepared, they are introduced into a reaction chamber illustrated by process block 102A. " While in the chamber the polysemiconductanes are pyrolytically decomposed as represented in process block 103A. Pyrolytic decomposition involves the effect of heat at a suitable temperature on a gaseous material under con¬ sideration in converting the material into an amorphous semiconductor on the surface of the desired substrate. It is to be noted that by contrast with the prior art the polysemiconductanes produced by pyrolytic decomposition do not display the hydrogen defect characteristic commonly found in the production of amorphous semiconductors from monosemiconductanes. As a result it is not necessary to subject the resulting product to hydrogen ion ' implantation or heavy doping. In particular, the invention is suitable for the pro¬ duction of amorphous silicon in accordance with the flow chart 100B of FIGURE IB. In this process, the polysemicon- " ductanes take the form of polysilanes in accordance with process block 101B. Once produced the polysilanes are intro¬ duced into a reaction chamber pursuant to process block ■ 102B. While in the chamber the polysilanes are subjected to heating in accordance with process block 103B. This decomposes them into amorphous silicon. The material is OMPI prepared under homogenous, controlled conditions at tempera¬ tures substantially less than necessary to decompose mono- silanes. In addition, the amorphous silicon product result¬ ing from the decompositon of polysilanes does not require subsequent treatment to compensate for hydrogen deficiencies. As in the case of semiconductors prepared in accordance with -the flow chart of FIGURE 1A, the amorphous silicon produced in accordance with FIGURE IB is generally useful in a wide variety of semiconductor devices. In the general case, amorphous semiconductors produced in accordance with the invention can be substituted for semiconductors produced in other ways in a wide variety of semiconductor devices. This is particularly true of photovoltaic, photoconductive and current rectification devices. In the case of polysilanes, useful members include disilanes, trisilanes, tetrasilanes pentasilanes and hexa- silanes. Isomeric members of the family are also suitable. The only limit on the class of useful members is governed by the stability of the polysilanes involved in the desired reaction. As the order of polysilanes increases there is a reduction in overall stability but this usually can be compen¬ sated by suitable operating condictions. Polysilanes that are decomposed pyrolytically may take the form of a mixture of polysilanes or be provided by a single polysilane alone. In addition,- as long as there is at least one polysilane present, the gaseous mixture may include a monosilane. This has the effect of reducing the the gaseous phase partial pressure so that operating condi¬ tions have to be adjusted accordingly. The gaseous mixture may further include dopants and inert gaseous carriers. A suitable operating pressure is about one atmosphere, but lower pressures may be employed as low as down to the pressure of about one Torr. The pressure desirably lies in the range from about one Torr to about 100 Torr in order 1 in part from the gas phase mixture. Very high order silanes, for example beyond hexasilane ha little effect on the production of the desired amorphous silicon film at standard temperatures and pressures because they have ne 5 gible vapor pressures at room temperature. However, when the higher order silanes are heated to produce a significant vapor pressure, for example above one millimeter of mercury, they also can provide high quality amorphous silicon film. An illustrative arrangement for preparing amorphous semic 10 ductors in accordance with the invention is illustrated in FIGURE 2A and 2B. The arrangement is in two sections, 210 for the prod tion of suitable semiconductanes and 250 for the conversation of the semiconductanes to the desired amorphous semiconductors. The arrangement 210 is specifically adapted for the produc 15 tion of amorphous silicon by pyrolytic decomposition, but it will be understood that appropriate modifications may be made for the production of other amorphous semiconductors. The arrangement 21 includes a reaction chamber 211, an acid source 212, a suicide source 213 and a series of traps 214,215. 20 In the. illustrative conversion section 250, reactans, incl ding the selected polysilanes, are applied to a reaction chamber 260 in the form of an envelope 261. The reaction chamber 260 ill tratively contains a substrate 262 upon which amorphous silicon is to be deposited. The chamber 261 is of a material which will 25 not contaminate the substrate 262. Suitable materials include quartz, glass and stainless steel. The illustrative reaction chamber 261 of FIGURE 2 has an inlet 263 and an outlet 264. The inlet provides entry for selecte polysilanes or a monosilane-polysilane mixture through a control 30valve 251 which allows the gaseous mixture to be supplemented by one or more dopant gases from sources 252 and 255. Postioned belo the inlet 263 is a support 256 for a holder 266 of the substrate 262. The substrate holder 266 illustrative is a cra idge heater with a wound ceramic core and a ceramic binder encompassing a re- 35 sistive element 266r. The latter is energized by suitable wiring which extends to the support along the holder. A stainless steel _ case isolates the ceramic core from the incoming gaseous stream represented by the arrow G. A manometer 270 is mounted on the chamber 261 to give an indication of the inter- ^-r- e T c r O PI 262. Suitable materials include quartz, glass, and stainless steel. The illustrative reaction chamber 261 of FIGURE 2 has an inlet 263 and an outlet 264. The inlet provides entry for selected polysilanes or a monosilane-polysilane mixture through a control valve 251 which allows the gaseous mixture to be supplemented by one or more dopant gases from sources 253 and 255. Positioned below the inlet 263 is a support 265 for a holder 266 of the substrate 262. The substrate holder 266 illustratively is a cartridge heater with a wound ceramic core and a ceramic binder encompassing a resistive element 2664. The latter is energized by suitable wiring which extends to the support along the holder. A stainless steel case isolates the ceramic core from the incoming gase- ous stream represented by the arrow G. A manometer 270 is mounted on the chamber 261 to give an indication of the internal pressure. The temperature of the substrate 262 is monitored by a guage (not shown) included in the wiring for the heater 266r. The substrate 262 is typically of glass. in order to make the desired amorphous silicon deposit the gaseous mixture G is passed over the substrate, being drawn toward the outlet 264 by the effect of a vacuum pump (not shown) . The substrate 262 is operated at a temperature in the range from about 350 β C. to about 500°C- resulting in pyrolytic decomposition of at least a portion of the gaseous stream G. The decomposition cospents are indicated by the arrows B shown in dashed line form- The balance of the gaseous mixture, in the form of an exhaust E, is drawn through the outlet 264. As an alternative to the dynamic system described above, a static deposition system nay also be used. In static deposition, the semiconductanes are introduced into the evacuated reactor through a valve- The exhaust and inlet valves are then shut, causing a specified volume of gaseous mixture to be trapped in the chamber. Because of SUBSTITUTE SHEET In addition, the electrical properties of the deposited amorphous silicon are controlled according to the nature of the dopant gases from the sources 252 and 255. For p-type doping, the dopant gas 252 can be a boron hydride such as B 2 H g , B τ n H i4' etc., while for n-type doping the dopant gas 255 is a phosphoru hydride such as PH., or _ _ • Alternatively, the desired dopant hydrides can be formed in the gas mixture by incorporating magn sium boride and/or magnesium phosphide in the reactants. It wi be appreciated that any of a wide variety of other dopants may be used. In some cases it is desirable for the same dopant gas to be selectively applied from two or more spearate sources, su as the sources 252 and 253. It is to be noted that the major portion of the gaseous mixture G desirably is of an inert carrier gas in order to inhi bit spontaneous combustion of the reactants in the event of the fracture of the chamber 261. While the substrate 262 of FIGURE 2 has been chosen as glass for reasons of economy, metal sub¬ strates, particularly steel, may also be employed. For depositing amorphous germanium, diger ane (Ge 2 Hg) ca be used and the deposition performed at a temperature in the range of 150°C. to 220°C. As an alternature to digermane, mon germane (GeH.) can also be used, but the rate of deposition is somewhat slower than for digermane. Other higher germanes can also be used, such as triqermane (Ge_H„) . 3 o The practice of the invention is further illustrated wit respect to the following nonli iting examples, as summarized in Table I τ in which the gases are high order silanes as prepared as heretofor described. OMPI gaseous mixture G desirably is of an inert carrier gas in order to inhibit spontaneous combustion of the reactants in the event of the fracture of the chamber 261. While the substrate 262 of FIGURE 2 has been chosen as glass for reasons of economy, metal substrates, particularly steel, may also be employed. For depositing amorphous germanium, digermane (Ge_H g ) can be used and the deposition performed at a temperature in the range of 150°C. to 220 β C. As an alternative to diger- mane, monogermane (GeH.) can also be used, but the rate of deposition is somewhat slower than with digermane. Other higher germanes can also be used, such as tigermane (Ge_Hg) . The practice of the invention is further illustrated with respect to the following nonlimiting examples, as summarized in TABLE I. ^0REA T OMPI LΠ RADIATION DARK RESIS- RESISTANCE (OHMS)* TANCE (OHMS) ADDITIVE PRESSURE TEMP. DEPOSITION THICKNESS OR RESISTIVITY OR RESISTIVITY EXAMPLE (PERCENT) (TORR) (°C) TIME (A°) (OHMS-CMS) (OHMS-CMS) I 65 390 2 hrs. 3,600 • II 65 410 2 hrs. 7,000 1.5 X io 10 OHMS 4.2 x IO 12 III 65 430 2 hrs. 7,000 1.5 X 10 10 OHMS 2.8 x io 12 IV 100 400 2 hrs. 11,000 8.0 X 10 9 OHMS 1.0 x io 12 V 100 420 2 hrs. 13,000 1.5 X 10 9 OHMS 2.0 x io 12 OHMS- •CM OHMS-CM * Under 70m /cm Detailed Description of Devices Amorphous semiconductors produced in accordance with th invention can be used to form a wide variety of semiconductor devices. It is important to note that the amorphous silicon films produced by the present invention are different from the usual glow discharge and high vacuum deposited films. Films according to the present invention are not subjected to ion da age. As an example"of the.-different characteristics of the present films and those of the prior art, FIGURE 2C compares the spectral response of a typical glow discharge film with a film according to the present invention. In the curves of FIGU 2C relative photovoltaic quantum efficiency is plotted against the wavelength of excitation radiation. It is apparent from FIGURE 2C that by contract with glow discharge films, amorphous silicon films produced by the invent have a spectral response with higher relative quantum efficienc and extend to larger wavelengths. In addition, by comparison with high vacuum deposited films, those " of the invention achieve significantly higher phot conductivity, e.g. 10 -6 to 10-4 ohms per centimeter (bhms-cm-1) as opposed to a range of 10 -9 to 10-7 ohms-cm-1 for the high vacuum deposited films of U.S. patent 4,237,150 and 4,237,151. One such device is the photodetector 300 of FIGURE 3. A glass substrate 301 with an amorphous silicon deposit 302 is provided with aluminum contacts 303 and 304 and connected in circuit through a * battery 305 to a load 306. When incident lig 307 falls on the amorphous silicon layer 302, it creats electro hole pairs which are acted upon by the voltage of the battery 305 and produce a corresponding voltage increase in the load 306 according to the number of hole-electron pairs created. Another device which makes use of amorphous silicon pro¬ duced in accordance with the invention is the heterojunction semiconductor device 400 of FIGURE 4. This device has differen junctions Jl and J2 between p-type material 403 and intrinsic (i-type) material 402 on the one hand, and between * the intrinsi material 402 and the n-type semiconductor material 401 on the __ OMPI ~ other hand. The bandgaps of the p- and n-type materials 403 and 401 are different than for the intrinsic material 402. Both the intrinsic material 402 and the n-type material 403 are forme by chemical vapor deposition. In the case of the n-type materia a-,dopant such as phosphine is included. The p-type material 403 is also made by chemical deposition with a suitable dopant, such as boron. In addition, the p-type materials gaseous stream in- " eludes methane or acetylene in order to produce a silicon carbon allow (a-(Si,C):H) . The resultant device 400 is a P-I-N semiconductor device controlled by a grid contact 404 and deposited desirably upon a substrate 405. The device 400 has the advantage over other similar devices of permitting a greater amount of light to enter the intrinsic layer 402 by virtue of the amorphous silicon carbo alloy layer 401, which has a higher bandgap than the intrinsic layer 402. In general, desirable semiconductive devices can be produc by substituting semiconductor layers prepared in accordance with the invention for semiconductor layers prepared by other techni- ques. For example, the various devices of illustrative U.S. pat ent 4,064,521 can be adapted in accordance with the present inve tion by substituting pyrolytically decomposed polysemiconductane for the glow discharge amorphous silicon of the prior art. The average density of localized states of the CVD amorpho silicon prepared from si n H 2n+ 2 n = 2-δ ) is believed to be or deduced to be from device performance to be in the 10 /cm to 10 /cm range, and much lower than that of amorphous silicon fabricated by other means, i.e., for sputtered or evaporated amo *" _ a phous silicon. The average density of localized states is 10 / cm or greater. This low density or defects states leads to longer depletion widths and low recombination, thus producing good quality devices. One such device is the Schottky barrier solar cell 500 of FIGURE 5 formed by a substrate 512 with a ' body 514 of amorphous silicon. The device 500 also includes a metallic layer 516, an interface 518, an antireflective layer 520, an incident surface 522 for solar radiation 526 and a grid electrode 524. If the surface resistivity of the electrode 628 at the first -doped layer is on the order of about 10 ohms/ or more, it is preferable to also have a gride contact like that descri¬ bed in FIGURE 5, on .the first doped layer 613 for collection of the current generated in the body 614. An electrical contact 627 is on the surface of the second doped layer 615 opposite the transmissive electrode 268. The electrical contact 627 is of a material having reasonable electr cal conductivity, such as aluminum, chromium, tantalum, antimony niobium or stainless steel. As previously described in FIGURE 5, the absorption coeffi cient of the amorphous silicon films prepared by chemical vapor deposition of s i n H 2n+2' w ^ ere n equals 2 through 6, is larger than that of a single crystal silicon in the visible range. For this reason only a thin layer of amorphous silicon is needed for sufficient solar radiation absorption. Typically the intrinsic region of amorphous silicon is about one micron or less in thick ness, while the first and second doped layers 613 and 615 are each a few hundred Angstroms in thickness. Referring to FIGURE 7, a semiconductor device 710 is a pho voltaic device, and more particularly a P-N junction solar cell. The photovoltaic device 710 includes a region 711 of amorphous silicon fabricated by the polysilane chemical vapor deposition • method in accordance with the invention, with appropriate doping gases. The region 711 comprises a first doped layer 752 of one conductivity in contact with a second doped layer 754 of an oppo site conductivity with a P-N junction 756 inbetween. For pur¬ poses of discussion, it is assumed that the first coped layer 752 is of p-type material and the second doped layer is of n- type conductivity. Both the first and second doped layers 752 and 754 are the body 714 of the photovoltaic device 710. The region 711 includes a third doped layer 758 on the surface of the second doped layer 754 which has a higher doping concentra¬ tion than the second doped layer 754. Thus the third doped layer 758 is of n-type conductivity. The third doped layer 758 assists in making ohmic contact in the body 714. Although the embodiments described in FIGURES 5, 6 and 7 have been described as solar cells, it is anticipated by the pre- OMPI sent invention that these embodiments can also be utilized as high frequency photodetectors, i.e., devices which respond to radiant energy. Referring to FIGURE 8, a further embodiment of the semico ductor device of the present invention is designated 810. The semiconductor device 810 is described as a heterojunction photo voltaic device for the purpose of explaining the sixth embodime of the present invention. The photovoltaic device 810 includes a body 814 of amorphous silicon fabricated by pyrolytic decom- position. The body 814 of amorphous silicon has the same chara teristics as the body 402 of the second embodiment of the prese invention. The fabrication of the photovoltaic device 810 is similar that of the embodiments previously described. The semiconducto 860 may function as the support in the conversion apparatus (as previously described in FIGURES 4 and 5) for the deposition of the body 814 of amorphous silicon. As an alternative method of fabrication, the body 814 can be formed by pyrolysis of disilan • and the semiconductor region 860 can then be sputtered onto the body 814. Next the first electrode 866, the intermediate layer 868 and the second electrode 870 are formed by masking and evap ation techniques well known in the art. While the sixth embodiment of the present invention has been described as a photovoltaic device, it is obvious to those skilled in the semiconductor art that such a device can also fu tion as a rectifier. If the device 810 was operated as a recit there would be no need for the semiconductor region 860 to beof material which is -semitransparent or transparent to solar radia tion. In addition, there would also be no need for an incident surface 854 which is capable of solar radiation impinging there While various aspects of the invention have been set fort by the drawings and specification, it is to be understood that t foregoing detailed descriptions are for illustration only and th various changes, as well as the substitution of equivalent cons tuents for those shown and described may be made without departi from the spirit and scope of the invention as set forth in the appended claims. OMPI can also function as a rectifier. If the device 430 was operated as a rectifier, there would be no need for the semiconductor region 860 being of a material which is semi- transparent or transparent to solar radiation. In addition, there would also be no need for an incident surface 864 which is capable of solar radiation impinging thereon. While various aspects of the invention have been set forth by the drawings and specification, it is to be understood that the foregoing detailed descriptions are for illustration only and that various changes, as well as the substitution of equivalent constitutents for those shown and described may be made without departing from the spirit and scope of the invention as set forth in the appended claims. -17A- Nomenclature of Devices (Figs. 3-8) 300 Photodetector 301-glass substrate 302-amσrphous ' silicon deposit 303-aluminum contact 304-aluminum contact 305-battery 306-load 307-incident light 400 Heterojunction Device 401-n-tyρe material 402-intrinsic material 403-p-type amorphous silicon carbon alloy 404-grid contact. 405-substrate 500 Schottky Barrier Photovoltaic Device 512-substrate 514-amorphous silicon body 516-metallic layer 518-interface 520-antireflection layer 522-incident surface 524-grid electrode 526-solar radiation 10 P-I-N Photovoltaic Device 613-first doped layer 614-amorphous silicon body 615-second doped layer 617-intrinsic layer 626-solar radiation 627-electrical contact 628-transmissive electrode 629-incident surface 10 P-N Photovoltaic Device 711-amorphous silicon 714-body of device 726-solar radiation 728-transmissive electrode 729-incident surface 752-first doped layer 754-second doped layer 756-P-N junction 757-electrical contact 758-third doped layer 10 Heterojunction Photovoltaic Device 814-amorphous silicon 826-solar radiation 854-incident surface 860-semiconductor 862-heterojunction 866-first electrode 868-intermediate layer 870-second electrode OMPI

Claims: - - WHAT IS CLAIMED IS: 1. A method of preparing amorphous semiconductor which comprises pyrolytically decomposing one or more gaseous phase polysemiconductanes at a temperature below about 500°C. 2. The method of claim 1 wherein the pyrolytic decompo- sition takes place at a temperature in the range from about 300 to about 500°C. 3. The method of claim " 2 wherein said temperature is in the range from about 350°C. to about 450°C. 4. The method of claim 1 wherein the pyrolytic decompo¬ sition takes place at a partial pressure of greater than about one micron of mercury and less than about one atmosphere. 5. The method of claim 4 wherein said pressure lies in the range from about one Torr. 6. The method of claim 5 wherein said pressure lies in the range from about one Toϊr to about 100 Torr, thereby to lim gas phase nucleation of particles. 7. The method of claim 1 wherein said polysemiconductan are selected from the class ranging from disilanes to and inclu ing hexasilanes represented by the formula Si H. «, where n ranges from two to six. 8. The method of claim 1 wherein said gaseous phase in¬ cludes one or more dopant gases. 9. The method of claim"8 wherein said dopant gases are selected from the class including phosphorus and boron contain¬ ing gases. 10. The method of claim 9 wherein said phosphorus conta ing gas is phosphine (PH,) and said boron containing gas is di- borane (B-Hg) . 11. The method of claim 1 wherein said gaseous phase includes an inert gas carrier. 12. The method of claim 11 wherein said inert gas carri is argon or helium. 13. The method of claim 1 wherein one or more of said polysilanes are decomposed on a heated substrate. - 14. The method of claim 13 wherein the decomposition takes place at the temperature of the substrate. O PI W --15- 15. The method of preparing an amorphous silicon semicon¬ ductive device which comprises the steps of: (a) forming a body by pyrolytically decomposing one or more gaseous phase polysilanes, and (b) providing one or more contacts to said body. 16. The method of claim 15 wherein said body is formed on a substrate. 17. The method of claim" 15 wherein said body is formed by a plurality of separate decompositions each forming a separate layer. 18. The method of claim 17 wherein one or more of said layers include dopants therein. 19. The method of claim 18 wherein the doped layers are of one or more conductivity types. 20. The method of claim 19 wherein the conductivity types include p and n. 21- The method of claim 17 further including the provi¬ sion of a metallic interface with one ' or more of the deposited layers. 21. The method of claim 19 further including the provi¬ sion of an anti eflection layer in said device. 22. The method of preparing an amorphous semicond ctor Schottky device which comprises the steps of: (a) forming a heavily doped amorphous silicon layer on a conducting substrate by pyrolytic decomposition, of one or more polysilanes and a dopant; (b) depositing an undoped amorphous silicon layer on the said doped layer by pyrolytic decomposition of one or more poly- silajips . (c) depositing a metal on said undoped layer to form a Schottky barrier. 23. The method of preparing an amorphous silicon junction ■ device which comprises the steps of ( a ) forming a first doped a-Si layer on a conducting sub¬ strate by pyrolytic decomposition of one or more polysilanes and a " dopant; OMPI (b) forming a second doped a-Si layer on the said first doped layer by pyrolytic decomposition of polysilanes and a dopa (c) forming third doped a-Si layer of a conductivity type opposite to that of the " first doped layer on top of the lig ly doped layer by pyrolytic decomposition of polysilanes and a dopant; (d) providing a conducting ohmic contact to the second doped layer. 24 The method of claim 23 wherein the second doped a- Si layer is substituted for an undoped a-Si layer, deposited by . pyrolytic decomposition of one or more polysilanes. 25. The method of producing a solar photovoltaic device according to claim 22 wherein the Schottky barrier is semitrans¬ parent to solar radiation. __6. The method of producing a solar photovoltaic device according to claim 22 wherein the conducting substrate is semi- transparent to solar radiation. 27. The method of producing a solar photovoltaic device according to claim 26 wherin the conducting substrate is glass covered with a semitransparent conducting electrode. 28. The method of claim 27 wherein the semitransparent conducting electrode is doped tin oxide (Sn0 2 ) or indium oxide (ln 2 0 3 ) or an alloy thereof. 29. The method of producing a solar photovoltaic device according to claims 23 or 24 wherein either the ohmic contact or the conducting substrate is semitransparent to solar radia¬ tion. 30. The method of producing a solar photovoltaic device according to claim 23 or 24 wherein the conducting substrate is a metal ' upon which the amorphous silicon junction device is de¬ posited and the ohmic contact is semitransparent to solar radia¬ tion. 31. The method of producing a solar photovoltaic device according to claim 29 wherein the conducting substrate is glass coated with a semitransparent conducting electrode. 32. The method of producing a solar photovoltaic device according to claim 31 wherein the semitransparent conducting elec trode is doped tin oxide (Sn0 2 ) indium oxide (ln 2 0,) , or an alloy thereof. . -2.1 - 33. The method of producing an amorphous silicon semiconducting heterojunction device which comprises the steps of: (a) forming a first doped a-Si layer on a conducting substrate by pyrolytic decomposition of one or more polysi¬ lanes and a dopant; (b) forming a second doped a-Si layer on the first doped layer by the pyrolytic decomposition of one or more polysilanes and a dopant; (c) depositing a doped semiconductor material of a polarity type which forms a heterojunction with the second doped layer thereon, the heterojunction so formed being of an opposite polarity type to the type of the junction formed between the first doped layer and the second doped layer; and (d) providing a * ohmic contact to the semiconductor material of step (c) . 34. The method of producing the device of claim 33 " wherein " the said semiconductor material is selected from a class consisting of gallium arsenide (GaAs) , silicon (Si) , indium oxide (In, 0,) , tin oxide (SnO-) , alloys of indium oxide and tin oxide, cadmium sulfide (CaS) , zinc sύlfide (ZnS) , and alloys of cadmium sulfide and zinc sulfide. OMPI WIPO -22- 35. The method of producing the device of claim 33 * wherein the semiconducting material has a larger bandgap than the second doped a-Si layer. 36. The method of producing the device of claim 33 wherein the fabrication steps are reversed, namely the third doped semiconducting material forming the heterojunction is the substrate on which are successively deposited the said second doped a-Si layer and the first said doped a-Si layer, followed by forming ohmic contacts on the first and third doped semiconductor substrate. 37. The method of producing the device of claim 36 wherein the ohmic contacts are semitransparent to solar radiation. 38. The method of claim 37 wherein the said semitrans¬ parent contact is doped tin oxide (Sn0 2 ) or indium oxide (In-O.) , or an alloy of indium oxide, or an alloy of indium oxide and tin oxide. 39. The method of claim 33 wherein the said conduct¬ ing substrate is semitransparent to solar radiation. 40. The method of claim 39 wherein the semitransparent conducting substrate is glass coated with a semitransparent con¬ ducting electrode including doped Sn0 2 , In 0^, or an alloy of In-0, and Sn0 2 , or a thin metal film. 41 The method of claim 33 wherein the second doped a-Si layer is replaced by an undoped a-Si layer, deposited by pyrolytic decomposition of one or more polysilanes. 42. The method of claim 22 wherein said undoped a-Si layer is replaced by a doped layer, deposited by pyrolytic decomposition of one or more polysilanes and a dopant. 43. The method of claim 1 wherein said polysemiconductane are selected from the class ranging from digermanes to and in¬ cluding hexagermanes,represented by the formula Ge H_ 2 , where n ranges from two to six. 44. The method of claim 43 wherein the temperature of said decomposition is between 150°C. and 220°C.

Inventors: KISS ZOLTAN J, MACDIARMID ALAN G
Applicants: CHRONAR CORP, KISS ZOLTAN J, MACDIARMID ALAN G
Application year: 1982
Main classification: C01B33
IPC codes: C01B33, C23C16, H01L21, H01L29, H01L31