Zone Leveling and Solution Growth of Complex Compound 

Semi conductors in Space 

Final Report 

by Klaus J. Bachmann 

North Carolina State University, Raleigh, NC 27695-8204 

Professor of Chemistry and Materials Science and Engineering -- 

Concerning research funded by 

NASA Grant NAG 1-354 

Langley Research Center 

May 1, 1983 - September 30, 1986 

is cu. +GIN I Abstract 

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cro A research program on complex semiconducting compounds and alloys has been 

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completed that addressed the growth of single crystals of CdSeyTel-y, 

E.%:; I Zn,Cdl,xTe, MnXCdl-,Te, InP As 

'01 - I OW ' physico-chemical properties characterizing the above materials. 

and CuInSe2 and the measurement of fundamental 

The purpose of 

4 Ir1 b-4 t3 I Y 1-Y 

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(n incro 

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noc qvl this ground based research program was to lay the foundations for further 

cm $ $2 research concerning the growth of complex ternary compound semiconductors in 2 

t? H 

h, H 

0 kio microgravity environment. This work has resulted in 6 publications, 7 presen- t? zz 

GI tations at national and international meetings and supported the completion of 

> Cn a PhD thesis in Materials Science and Engineering by Mr. K. Y. Lay that was 

v 

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*a 2: successfully defended on 9.26.86. A research proposal concerning a follow-up &e (r 

(330 4 -.e I program incorporating a plan for a future flight experiment is being forwarded OLS, & 

u, h, 

2 to NASA Headquarters at this time. 

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1. Background Information 

During the period from July 1, 1983 to September 30, 1986 we conducted 

ground based research concerning the growth of bulk single crystals of 

semiconducting ternary compounds and alloys. The work on alloys relates to 

infrared optical imaging technology that is of interest to NASA's mission in the 

1 
context of satel 1 i te based sensors. 

vigorously as the presently most successful materials system for the fabrication 

of IR photodiode arrays and a detailed study of bulk crystal growth of this 

material is presently under way at Marshall Space Flight Center within the 

framework of NASA's Microgravity Science and Applications program (1,2). 

a related effort is made at the MIT concerning the growth of CdTe that is the 

most commonly used substrate for heteroepi taxial growth of CdZHgl-,Te (3). 

Both efforts are meaningful since photoconductive CdZHgl-,Te detectors fabricated from bulk single crystals still are important for a variety of IR applications while heteroepi taxial structures are better suited for the fabrication 

of diode arrays that are the primary sensing elements in focal plane sensor 

systems. Although the lattice mismatch of HgTe and CdTe, 0.3% at room temperature, is small it still leads to a substantial density of misfit dislocations 

at the CdZHgl-,Te/CdTe interface and to concomitant problems in the growth of 

abrupt double heterostructures and multiple quantum well heterostructures that 

are desirable for future advances in CdZHgl,Te technology. 

exists currently considerable interest in exactly lattice matching 11-VI alloy 

substrates that provide for lower defect density and improved metal 1 urgical 

interfaces. 

CdZHgl,Te bulk crystal growth, we added work on 3 alternative exactly lattice 

matching 11-VI alloys; CdSeyTel-,, ZnXCdl,Te and MnXCdl,Te; that completely 

cover the lattice constant range in the CdTe-HgTe pseudobinary system for 0 < z 

- < 1 and x, y < 0.1. 

known and exhibit in the cases of MnXCdl-,Te and CdSeyTel,y very narrow 

sol idus-1 iquidus separations for dil Ute a1 loys. 

are suitable for normal freezing type crystal growth techniques. The 

ZnXCdl,Te and CdZHgl,Te systems are characterized by wider sol idus-1 iquidus 

In particular, CdiHgl,iTe is being pursued 

A1 so, 

Therefore, there 

Although we started our program on 11-VI alloys with work on 

- 

The phase relations for the above 11-VI alloy systems are 

Therefore, these two systems 
separations that require the application of zone leveling to achieve axially 

uniform composition on a macroscopic scale. 

more complicated cases needing more sophisticated hardware and attention to 

constitutional supercooling in the selection of the growth rate. 

substantial Hg pressure must be sustained in thermal equilibrium with the 

mol ten zone for CdZHgl,Te which represents thus the experimentally most complicated case. 

of bulk vs. epitaxial CdzHgl,Te and because of the similarity of the fundamental research issues that are to be addressed in the context of materials 

processing in space in all 4 alloy systems, we tend now to give preference to 

MnxCdl,xTe and ZnXCdl,Te for reasons that will be presented more fully in 

section 2 of this report. 

Therefore, these systems present 

In addition, 

In view of the above assessment concerning the relative merits 

Ternary chalcopyrite structure isoelectronic analogs of the 111-V and 11-VI 

compounds of the type 11-IV-V2 and I-111-VI2 are of general interest for nonlinear optics applications since compounds with high figures of merit are known 

in both classes, e.g. ZnGeP2 and AgGaS2, respectively (4). Also, the unusually 

steep absorption edge of some of the I-111-VI2 compounds, e.g. CuInSe2 and 

CuInS2, makes these materials interesting candidates for photovoltaic solar 

energy conversion since the photogeneration of minority carriers proceeds in 

this case well within the depletion layer leading to almost maximum theoretical 

collection efficiency even in simple polycrystalline thin film solar cell 

structures. 

guaranty high power conversion efficiency, thin film CUI~S~~/Z~~C~~-~S solar 

cells with 12.5% power conversion efficiency a AM1 and excellent stability have 

been reported by several industrial research groups (5). 

solar cells are unusually resistant to radiation damage. 

property and the light weight of thin film CdS/CuInSe2 or ZnO/CuInSe2 cells 

they are of potential use for space applications. 

A1 though efficient carrier collection alone is not sufficient to 

Also, CuInSe2 based 

Because of this 

Further improvements by the 

3 
u t i l i z a t i o n o f I-111-VI, alloys and tandem cell structures in combination with L 

-Si:H appear to be possible which motivated an extensive study of the fundamental properties of CuInSe2 (7-10) and its alloys with CuInS2 (11,121 and CuGaSe2 

(13) in our laboratory. 

with SERI, and we comment in this report only on those aspects of our research 

A major part of this work was pursued under contract 

that are relevant to the microgravity related research covered in this project. 

There exists a considerable incentive for continuing research on CuInSe2 in the 

context of materials processing in space since this material represents a model 

case for the melt growth of a non-cubic semiconductor with specific problems 

that could be overcome in a microgravity environment and that will have a 

significant impact on other technological developments. Further details will 

be presented in sections 3 and 4. 

In addition to the above work on 11-VI alloys and on their I-111-VI2 

isoelectronic analogs we pursued research concerning InPyAsl-y and CdSnP2 that 

are examples of 111-V ternary alloys and their 11-IV-V2 isoelectronic analogs. 

Although we continue to have an interest in these two systems we believe that 

in view of the high decomposition pressures and safety risks in handling 

InPyAsl-y and the limited access to experimentation in space the above identified 11-VI and I-111-VI2 systems are more important for further exploration. 

For an assessment of critical research issues concerning the above ternary 

compounds and alloys we refer to the attached preprint of an invited paper 

presented at the 7th International Conference on Ternary and Multinary Compounds, Snowmass, Colorado, September 10-12, 1986 (14). 

2. Training of Graduate Students, Research Interactions and Conference 

Presentations 

The funding provided by this grant supported fully the research of one 

graduate student of Materials Science and Engineering, Mr. K. Y. Lay and helped 

through research interactions in the education of three other graduate stu4 
dents, Ms. N. Giles-Taylor and Mr. K. Park in the Department of Physics, and 

Mr. B. Abid in the Department of Chemistry. Mr. Lay started his thesis on The 

Growth and Characterization of CdTe-Based 11-VI Alloys in May 1983 and successfully defended this thesis on September 26, 1986. 

at 11-VI Inc., Saxonburg, Pennsylvania where he will pursue further research on 

11-VI alloy systems for infrared applications. 

He has accepted a position 

Three post-docs, Dr. P. Lange and Dr. H. Goslowsky from the Hahn-Meitner 

Institut, Berlin, FRG and Dr. H. Neff of Brown Boveri & Cie, Baden, Switzerland, who were supported primarily through other research programs contributed 

to the research covered by this report. 

of Prof. J. F. Schetzina and Prof. G. Lucovsky of the Department of Physics at 

NCSU in our early photoluminescence studies and in the XPS measurements, respectively. The UPS measurements on our MnXCdl,Te were performed by Dr. R. 

Kotz of Brown Boveri & Cie, at Baden, Switzerland. 

The results of our work were presented by Mr. Lay at the First State-ofAlso, we acknowledge the expert help 

the-Art Program on Compound Semiconductors (SOTAPOCS), ECS Meeting, New 

Orleans, Louisiana, October 9-10, 1984 and at the MRS Workshop on Materials 

Characterization, Research Triangle Park, NC, September 17, 1985. The PI 

presented a contributed paper at the International Conf. on Crystal Growth, 

York, England, July 14-16, 1986 and two invited papers at the PYA R&D Meeting, 

Denver, Colorado, May 13-15, 1986 and at the 7th International Meeting on 

Ternary and Mu1 tinary Compounds, Snowmass, Colorado, September 10-12, 1986. 

Further presentations by Mr. Park at the MRS Symposium on Diluted Magnetic 

(Semimagnetic) Semiconductors and an invited paper by the PI at the MRS Symposium on Materials for Infrared Detectors and Sources will be included into 

the Fall Meeting of the MRS, December 1-6, 1986 at Boston, Massachusetts. 

5 
3. Technical Results 

The growth of CdSeyTel-y, MnXCdl-,Te and CuInSe2 crystals was carried out 

in a modified vertical Bridgman furnace while InPyAsl-y and ZnXCdl,Te were 

grown by horizontal zone leveling, in the latter case using liquid encapsulation 

with B2O3 to counteract physical vapor transport from the molten zone to the 

colder parts of the fused silica enclosure. Photoluminescence and electron 

microprobe scans of the 11-VI alloys showed axially uniform composition of the 

alloys on a macroscopic scale although striations on a microscopic scale were 

revealed by etching for InPyAsl-,,. 

show deep luminescence features corresponding to the 1.42 eV deep emission in 

CdTe that is shifted by the band gap change of the alloys. 

consistent with the interpretation of this deep 1 uminescence as D-A transitions 

with minimum shifts in the depth ofthe relevant donor and acceptor levels upon 

alloying. However, in several alloy crystals, particularly MnXCdl,Te for x < 

0.2, no deep emission was observed. Also, room temperature band to band emisThe PL spectra of the three 11-VI alloys 

This result is 

sion was observed in selected crystals of CdSeyTel-y, 0 c y < 0.10. The -- 

twinning probability for comparable alloy concentration increased in the order 

CdSeyTel-y, ZnxCdl,Te, MnXCdl,Te while the microhardness increased in the 

order CdSeyTel,, MnXCdl,Te, ZnxCdl,Te. 

attached reprint of ref. 15. A study of the broadening of both the PL and 

photoreflectance (PR) signals shows that up to 20% Mn the spectra are dominated 

by a1 loy broadening while at higher concentrations extended defects become 

dominant (see attached reprint of ref. 16). Recent unpublished transmission 

electron microscopy studies reveal that these defects are planar domains of -40 

A thickness and up to 5000 A diameter that we characterize tentatively as 

microtwins. Figure 1 shows such microtwins in Mno.3Cdo.7Te. 

the pub1 i shed phase diagram of the pseudobi nary system CdTe-MnTe (17 1 suggests 

stable zincblende structure solid solutions up to x = 0.75 recent total energy 

For further detail s we refer to the 

However, a1 though 

6 
calculations (18) show that Cdn EMnnKTe should separate into CdTe and MnTe. 

Since the computation refers to zero K it does not necessarily pertain to room 

temperature, but further studies of the phase relations of the CdlWxMnxTe 

system below the solidus is needed to clarify this matter. 

controversy concerning alloys with x > 0.5 we restricted our investigation to x 

< 0.45. 

applications in conjunction with CdZHgl,Te solving the problem of twinning 

would be a major breakthrough in the technology. 

Since the substitution of Cd2+ by paramagnetic Mn2+ introduces localized 

".* v.* 

Because of the 

However, even for the dilute alloys that are suitable for substrate - 

magnetic moments there exist in MnXCdl,Te solid solutions interesting spinspin interactions between these localized magnetic ions and the extended 

states. 

that reveal for the first time decayed exciton contributions to the PC of 

Cdl,xMnxTe. The binding energy of the exciton decreases with increasing temperature in accord with the PL results in ref. 19 that suggest a magnetic localization of the excitons by interactions between the hole spin with the Mn2+. 

The s h i f t o f the binding energy towards the position of the free exciton line 

is thus explained as an increasing excitation of magnetically localized excitons into the free exciton state. 

Figure 2 shows results of PL and photoconductivity (PC) measurements 

Figure 3 shows the PC spectra for the same crystal at higher T. Note that 

after a maximum at lOOK the PC gain decreases to -160K and increases at higher 

T, i.e. it has a minimum at -2.0 eV. Figure 4 shows PL spectra of MnXCdl,Te 

as a function of x revealing 2.0 eV emission even at energy gaps Eg < 2 eV. 

This emission becomes dominant at values of x where Eg > 2 eV. 

observations establish unequivocally the existence of p-d transitions, i.e.. 

the communication of the Te p-level derived valence band edge with normally 

empty Mn d electron states that under the conditions of an optical transition 

The above 

7 
are located 2.0 eV above the valence band edge. The increasing band gap with 

increasing x is due to the upwards shift of the s-like conduction band edge upon 

replacement of Cd(5s) by Mn(4s) in the zincblende structure as indicated in the 

insert in fig. 5. 

terms of s-d exchange that has a maximum when the CBE coincides with the 

energetic position of the Mn d states. Also, the normal behavior in the PL at 

Eg < 2.0 eV reflects the usual excitation behavior between the VBE and the CBE 

while at Eg > 2.0 eV where the s-like CBE is located in energy above the Mn d 

states the latter act as a trap for photoexcited carriers dominating the recombination behavior. Since hot electrons trapped in Mn d 

even before they are located in energy below the CBE, above band gap 2.0 eV 

emission is observed for dilute alloy compositions. It should be mentioned 

that the above information is in conflict with the prevailing interpretation of 

optical transitions in MnXCdl,Te that are explained as intraion d-d* transitions (20). However, our results are consistent with recent unpubl i shed band 

structure calculations by Wei and Zunger that predict p-d transitions near 2.0 

eV and d-d* transitions at higher energies (21). Although clearly being a side 

product the above work is thus contributing to the understanding of the fundamental physical properties of diluted magnetic semiconductors which in view of 

their unusual magnetooptical properties deserve further attention. 

The minimum of the PC near Eg = 2.0 eV is interpreted in 

states can recombine 

In the context of substrate applications in CdZHgl,Te heteroepi taxy 

fundamental physical studies are important for the selection of the optimum 

material out of the 3 alloy systems under consideration. Because of the 

favorable microhardness of ZnXCdl,Te current crystal growth efforts by others 

almost exclusively focuses on this alloy. However, mechanical durability is 

not the only or even the most important selection criterion. 

successful epitaxy the native oxide and a layer of defective material under the 

native oxide generally must be removed by means commensurable with the epitaxial 

For example, for 

8 
method, i.e. in view of the strong emphasis of MBE for Cd,Hg,-,Te epitaxy under 

UHV conditions. 

ZnXCdl,Te and CdSeyTel,y is primarily Te02 as in the case of pure CdTe, but the 

native oxide on MnXCdl,Te consists of a mixture of MnO, and Te02 (see the 

attached reprint of ref. 22). 

technique reveals the existence of a 400 meV deep trap below the CBE and a 

L *L 

An XPS study of the 3 alloys reveals that the native oxide on 

In the case of MnXCdl,Te a double beam PC 

considerable enhancement of the surface recombination rate for the oxidized 

surface (compare the attached preprint of ref. 23 for details). Although 

similar studies for ZnXCdl,Te and CdSeyTel,y are still incomplete detrimental 

surface properties are, a1 so, expected after oxidation for these alloys. 

As favorable method for the fabrication of oxide free clean surfaces we 

explored sputter cleaning combined with subsequent low temperature annealing of 

the substrates. As shown in ref. 22 (see attached reprint) MnXCdl,Te is far 

less susceptible to damage than pure CdTe and recovers after 30 min annealing 

at 200°C to the undamaged state while the CdTe lattice cannot be restored at 

200°C even on extended annealing cycles. PL spectra reveal the generation of 

shallow and deep defect levels in CdTe, but only a slight increase in the 

concentration of shallow levels in MnxCdl,xTe after sputter cleaning. Both 

CdSeyTel-y and ZnXCdl,Te damage substantially during sputter cleaning as 

demonstrated by figs. 6-12 that show the PL spectra and PR spectra prior and 

after 5 kV Ar' exposure to comparable dose for the 3 alloys under consideration 

(24). 

outstanding the information gathered thus far favor MnxCdl,xTe over ZnXCdl,Te 

in terms of their surface properties. 

Although the annealing studies on CdSeyTel-y and ZnXCdl,Te are still 

An issue that has not been addressed yet 

and is of considerable importance for the development of devices is the relative response of the two materials systems to extrinsic doping. 

MnXCdl,Te and ZnXCdl,Te are nominally undoped of p-type and n-type conducSince 

9 
tivity, respectively, and compensation is expected to be associated with difficulties the preferred substrate choice may depend on tne application. However, 

more work is required to clarify this point. 

In order to perform intelligent crystal growth on ternary compound seniconductors detailed knowledge of their phase diagrams is imperative. 

shows the liquidus surface of the Cu,In,Se system (7) that exhibits extended 

regions of immiscibility in liquid state which must be avoided during the 

synthesis stage of the compound frm CU.~I~.~ and elemental selenium. 

priate procedures for doing this are established in our laboratory. 

13 reveals that all congruently melting ternary compounds in the system are 

located at the Cu2Se-In2Se3 pseudobinary. 

gram on this pseudobinary cut in the range 0 < x < 0.5. 

melting point on this pseudobinary is on the In2Se3-rich side of CuInSe2 that 

consequently cannot be grown from the stoichiometric melt. 

stoichiometry is obtained by zone leveling using a Cu-rich liquidus composition 

and is extremely important in this materials system because of the wide y phase 

region that extends several % to In2Se3 rich composition at room temperature. 

The properties of CuInSe2 depend drastically on the position within the hmogeneity range which is documented in detail in refs. 8-10. 

Figure 13 

ApproAlso, fig. 

Figure 14 shows the T-xIn Se dia23 

-- Note that the maximum 

Control of the 

In the context of the Microgravity Science and Applications program the 

following problems of CuInSe2 crystal growth are of interest: 

zone leveling experiments under ground based conditions it is difficult to 

suppress nucleation on the bat walls (preferably pyrolytic BN). 

growth rate of CuInSe2 is highly anisotropic (slowest perpendicular to the (112) 

face) the texture of the polycrystalline skin generated on the walls favors their 

overgrowth by a single crystaliine sheet nucleated with (iiZ) paraiiei to the 

free surface. 

keeping the top surface at a lower temperature than the bottom of the 

1. In horizontal 

Since the 

The thickness of this sheet is maximized by a vertical gradient 

10 
boat. However, such a gradient presents unfavorable conditions with regard to 

convective cell formation, and completely single crystal1 ine ingots cannot be 

made at this time. This in turn causes problems related to saving the crystal 

through the sol id state transformations at 85OoC and 81OoC, respectively, that 

are revealed by DTA (compare fig. 10) and to prevent crack formation during 

cooling to room temperature. 2. Vertical Bridgman growth is more successful 

than horizontal zone leveling to obtain single crystals, but does not provide 

for axially uniform composition. Even in Bridgman growth the generation of a 

convex solid-liquid interface is difficult and distortions either in the form 

of a thin polycrystalline peripheral region or twinning are observed due to 

container effects on the interface shape. 

can be circumvented under microgravity conditions where decoupling of the 

molten zone is possible as described in our original proposal. 

value of a supply of stoichiometric well characterized crystals for research 

and development efforts on CuInSe2 based devices, particularly in the context 

of further assessments of the utility of this material in a hostile radiative 

environment, there exists considerable interest in improved growth methods that 

may become available as part of NASA's Microgravity Science and Applications 

program. 

4. Proposed Future Work 

We believe that these difficulties 

In view of the 

Based on the above data we believe that a more focussed follow-up program 

would be meaningful on the growth of MnXCdl,Te by the Bridgman method and of 

CuInSe2 by zone leveling. 

tially exists at present or is under active development at Marshall Space 

Flight Center would be suitable for an experiment with Mn,Cdl,Te, - A substantial arsenal of characterization tools and experience with this material exists 

at the PI'S laboratory so that the apparatus and procedures for comprehensive 

In our opinion, space approved hardware that essen11 
characterization of crystals grown in a microgravity environment are in place. 

Before such an experiment is executed modeling should be performed of the 

chosen geometry. Although certain experiments on the ground in support of 

modeling and computer simulations of the planned space experiment will be 

necessary in the initial phase of a follow-up program planning for such an 

experiment could resume immediately. 

A continuing effort on zone leveling appears to be desirable, but should 

focus on CuInSe2 which is of larger significance as compared to ZnXCdl,Te in 

terms of potential for generating new scientific information. In both 

MnXCdl,,Te and CuInSe2 crystal growth the decoupling of the melt from the 

container walls will be the key issue for requesting access to a microgravity 

environment. 

effects are important in the control of the interface shape and may affect the 

convective flow in both Bridgman and zone leveling geometries. Also, container 

interactions greatly affect the quality of both CuInSep and Cdl,MnXTe crystals 

grown at 1 g by assisting the nucleation of twins and polycrystalline peripheral regions. The effects of at least partial decoupling of the melt from 

the container can be studied at 1 g and work on this aspect is incorporated 

into the research plan for ground based activities in the first 12-18 months of 

the schedule of work of the proposed continuation. Also, in this schedule we 

include exploratory research on compensation doped InSb that has not been part 

of the present activity. 

activity will not require extra funds since the growth and characterization 

tools are already established in the context of the above program on MnXCdl,Te 

and CuInSe2. 

As has been shown for both Cd,Hgl,Te (25) and CdTe (2) container 

In terms of capital equipment expenditures this added 

12 
Re fer e nce s 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

S. L. Lehoczky and F. R. Szofran, Materials Processing in the Reduced 

Gravity Environment of Space, Vol. 9, G. E. Rindone, ed., North Holland 

Pub1 ., NY 1982, p. 409. 

R. K. Crouch, Microgravity Science and Applications, Report on a Workshop, 

Pasadena, CA, 1984, National Academy Press, Washington, DC, 1986. 

T. Jasinski and A. F. Witt, J. Crystal Growth 71, 295 (1985). 

3. L. Shay and J. H. Wernick, Ternary Chalcopyrite Structure 

Semiconductors: Growth, Electronic Properties and Applications, Pergamon 

Press, Oxford, 1975. 

R. A. Mickelsen and W. S. Chen, Proc. 16th IEEE Photovolt. Specialists 

Conf., San Diego, CA, 1982, p. 481. 

D. L. Morell, K. Mitchell, R. Wieting, R. Potter, C. Eberspacher, D. 

Tanner and C. Fairchild, Conf. Rec. 18th IEEE Photovolt. Specialists 

Conf., Las Vegas, NV, 1985, p. 876. 

K. J. Bachmann, M. L. Fearheiley, N. Tran and Y. H. Shing, Appl. Phys. 

Lett. 44, 407 (1984). 

P. Lange, H. Neff, M. Fearheiley and K. J. Bachmann, J. Electrochem. SOC. 

132, 2281 (1985). 

P. Lange, ti. Neff, M. Fearheiley and K. J. Bachmann, Phys. Rev. B31, 4074 

(1985). 

10. M. L. Fearheiley, Y. H. Shing, S. Vasquez, C. Herrington and K. J. 

Bachmann, J. Electron. Mater. 14, 677 (1985). 

11. H. Neff, P. Lange, M. L. Fearheiley and K. J. Bachmann, Appl. Phys. Lett. 

47, 1089 (1985). 

12. P. Lange, H. Neff, M. L. Fearheiley and K. J. Bachmann, J. Electron. 

Mater. 14, 667 (1985). 

13. B. Abid, H. Neff and K. J. Bachmann, J. Electrochem. SOC. 1986, submitted. 

14. K. J. Bachmann and H. Goslowsky, Proc. 7th Int. Conf. on Ternary and 

Multinary Compounds, S. Deb and A. Zunger, eds., Snowmass, CO, 1986, to be 

pub1 i shed. 

15. K. Y. Lay, N. Giles-Taylor, J. F. Schetzina and K. J. Bachmann, J. 

Electrochem. SOC. 133, 1049 (1986). 

16. K. Y. Lay, H. Neff and K. J. Bachmann, phys. stat. sol. (a)92, 567 (1985). 

17. R. Triboulet and G. Didier, J. Crystal Growth 52, 614 (1981). 

18. S. H. Wei and A. Zunger, Phys. Rev. Lett. 56, 2391 (1986). 

13 
19. H. Neff, K. Y. Lay, R. Kotz and K. J. Bachmann, J. Lumin. 1986, accepted. 

20. Y. R. Lee and A. K. Ramdas, Solid State Commun. 51, 861 (19841, R. Y. Tao, 

M. M. Moriwaki, W. M. Becker and R. R. Galazka, J. Appl. Phys. 53, 3772 

(1982 1. 

21. S. H. Wei and A. Zunger, private communication of unpublished results. 

22. H. Neff, K. Y. Lay, B. Abid, P. Lange, G. Lucovsky, and K. J. Bachmann, J. 

Appl. Phys. 60, 151 (1986). 

23. K. Park, H. Neff and K. J. Bachmann, Proc. MRS Symp. Diluted Magnetic 

(Semimagnetic) Semiconductors, Aggarwal, ed., 1986, to be published. 

24. K. Y. Lay, H. Neff and K. J. Bachmann, unpublished results. 

25. R. J. Naumann and S. L. Lehoczky, J. Crystal Growth 61, 707 (1983). 

14 
ORlGlNAL PAGE IS 

OF POOR QUALITY 

Figure 1. A TEM photograph of a crystal of CdOe7Mnoe3Te. 

15 
I I I 

PL 

13KL 

I 

PC 

100 K 

< 

75K, 

1.6 1.8 2.0 2jJ 2.0 22 2.4 

PHOTON ENERGY / eV 

2. Photoluminescence (left side) and photoconductivity spectra 

(right side) recorded in the temperature regi;rC 13K -- c T c 

100K. The band gap position is denoted by a vertical bar 

in the PC spectra. 

16 
Figure 

I 1 I I I I I 

1.4 1.6 1.8 2.0 22 23 2.4 

PHOTON ENERGWeV 

Photoconductivity spectra recorded in the temperature 

regime 100K -- < T < 230K. 

17 
X:lB x G 3 X: 43% 

1 

400 

PHOTON ENERGY lev] 

Figure 4. Photoluminescence spectrum obtained at 12K for 

Cd0.82Mn0,1 gTt. 

1.99 eV that occurs 100 mV above the excitonic PL-band at 

1.9 eV. 

Note the expanded PL-si gnal centered at 

18 
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Photon Energy/ eV 

Figure 6. The photo1 uminescence spectra of CaTe ana Csi0.8Mn0.2Te in 

the as cleaved (full lines) and (110) oriented surface and 

the surface upon 30 min Ar-ion sputtering (dashed lines). 

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