OMVPE growth of GaInAs

Journal of Crystal Growth 64 (1983) 461—470 North-Holland Publishing Company

OMVPE GROWTH OF GaInAs

461

*

C.P. KUO, R.M. COHEN and G.B. STRINGFELLOW Department of Materials Science and Engineering and Electrical Engineering, University of Utah, Salt Lake City, Utah 84112, USA

Received 31 August 1983

The growth of the promising semiconductor alloy GaInAs by OMVPE has been studied using organometallic vapor phase epitaxy (OMVPE). The growth process and materials properties have been studied and compared for growth using triethyl-group III sources (TEGa+TEIn) and trimethyl-group III sources (TMGa+TMIn) in an atmospheric pressure OMVPE apparatus. The most significant disadvantage of using triethyl sources, as opposed to trimethyl sources, is their greater propensity to participate in parasitic gas phase reactions which deplete Ga, and especially In, from the gas phase upstream from the substrate. This results in low growth efficiency and a temperature dependent growth rate and solid composition. Control of growth rate, morphology and solid composition are discussed in detail. The electrical and optical properties are also presented for comparison.

1. Introduction GaInAs is a Ill/V semiconductor alloy potentially useful for ultra-high speed FET’s [1] and detectors for fiber-optic links operating in the wavelength region between 1.3 and 1.6 j.Lm [21.The alloy composition Ga0471n053As is lattice matched to the InP substrate. This alloy has a band gap of 0.75 eV (corresponding to a wavelength of 1.65 ~tm) and room mobilities 2/V. stemperature have been reported [3].as high as 13,000 Earlycmresearch on GaInAs concentrated on material grown by liquid phase epitaxy (LPE) [3]. More recently the vapor phase epitaxy techniques molecular beam epitaxy (MBE) [4], hydride VPE [5] and organometallic vapor phase epitaxy (OMVPE) have successfully produced high quality material [6]. The earliest report of OMVPE growth of GaInAs was in 1973, by Manasevit and Simpson [7], using trimethylgallium (TMGa) and triethylindium (TEIn) plus AsH 3. This approach was repeated by Baliga and Ghandi [8] and Noad and Spring Thorpe [9].However, using TEIn and AsH3, a parasitic gas phase reaction occurs to deplete In from the vapor upstream from the substrate. This *

was reported to produce several significant problems; low growth rate, difficulty in obtaining high In content alloys, and inhomogeneous and difficult-to-control solid composition. Two approaches to solve this problem have been to use low pressure reactors [10—13]or to use adducts as In sources [14—16].In the former case the reactants are together too short short a time to allow reaction. Using adduct sources inhibits the reaction between In shown source toand AsH3.device Both quapproaches havethe been produce ality GaInAs with few difficulties. However, both approaches necessitate considerably more complex apparatus [10,17], and still have very low reaction efficiencies [6,14,18]. Hsu et al. have reported the successful growth of InP [19] and GaInP [20] in an atmospheric pressure reactor using TMIn, without the difficulties described above for TEIn. Sacilotti et al. [21] have also reported that TMIn can be used to produce InP and GaInAs without the need for either low pressure or adduct sources. The purpose of this paper is to present a study and comparison of the growth and characteristics of GaInAs using the ethyl-group III sources and the methyl-group III sources.

Supported by the Army Research Office DAAG29-83-K-0153.

0022-0248/83/0000—0000/$03.00

©

1983 North-Holland

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OMVPE growth of GalnAs

2. Experimental The OMVPE reactor used in this study is shown schematically in fig. 1. The SiO2 reactor tube has a cross section 2 cm high by 5 cm wide. Separate inlet tubes for the group III and group V reactants were used for all runs using the ethyl sources. For the methyl sources the group III and group V reactants were more completely mixed by forming a single nozzle just inside the entrance with no ill effects. IR from a focussed lamp is used to heat the graphite susceptor. The plumbing is all stainless steel, with welded joints where practical, automatic flow controllers on all lines, and air activated bellow valves used throughout. The reactor is operated at 1 atm pressure. The organometallic source materials are held in temperature controlled baths (23°Cfor TEIn, 15°Cfor TEGa, 12°Cfor TMGa, 10°Cfor TMIn and 15°Cfor TMAs). The AsH3 is obtained diluted to 10% in H2 from a high pressure cylinder. The ambient is H2 purified by diffusion2 through a Pd cell. Substrates large as can be accommodated on the as susceptor. 2 x 3 cm (100) InP substrates were prepared using Br and methanol just prior to introduction into the reactor. The layers were characterized by measuring photoluminescence (PL) spectra and Hall effect using the Van der Pauw geometry. The PL was excited using the 488 nm line of an Ar* laser with an excitation intensity of —20 mW on a 100 ~tm —

Susceptor

Gas Inlets

Gas

Outlet

~~/Substrate

~

L—H-J

1~j~ r~1

-—

Shield~

LMJ

~ThermocoupIe

/ / Elliptical Mirror ~Lamp

Fig. 1. Schematic diagram of atmospheric pressure, horizontal, RF heated OMVPE reactor used in this work,

diameter spot. The emission was detected using a Spex ~ m spectrometer and a 77 K Ge p—i—n detector. Room temperature spectra were corrected for system response to obtain the composition and the half-width. The much narrower 77 K spectra are plotted in this paper directly as obtamed from the spectrometer with no correction for spectral response.

3. Results Experimental data will first be represented for the growth of GaAs, InAs and GaInAs using ethyl-group III sources TEIn + TEGa. Then the experimental data using the methyl-group III sources TMIn + TMGa will be added for comparison. 3.1. GaAs—TEGa

For rate, r the growth of GaAs using TEGa the growth 5, is found to be a linear function of group III molar flow rate, f~,and to be independent of the group V molar flow rate. This is generally true for all systems investigated in this study. Thus, the growth efficiency (i-5/f111) is plotted versus substrate temperature in fig. 2. Consider first the use of AsH3 as the group V source. The exact growth conditions are f(TEGa)= 16 ~smoI/min, f(A5H3) 400 ~smol/min and f(H2)= 2.0 liters/mm. The growth efficiency is in the range of 2 x i0~to 5 X 10~~sm/mol, in the entire temperature range from 480 to 650°C. The growth efficiency ap=

parently decreases slightly with increasing temperature. This value of growth efficiency is rather low, indicative of some depletion of Ga due to parasitic pre-reactions [18]. The low temperature growth is interesting because at temperatures below 550°C. using TMGa at a V/Ill ratio of 8.0, Krautle et al. [22] reported a fall-off in growth rate. Perhaps the very high effective V/Ill ratio (taking into account

Ga depletion) produces the temperature independent growth rate seen in the present results. The use of TMAs has been reported to reduce parasitic reactions in OMVPE growth of Ill/V alloys [16]. However, when TMAs was substituted for AsH 3, the reaction efficiency was largely un-

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463

OMVPE growth of GalnAs

I (SC) 700 I

650 I

600

576

560 I

525

500 F

480 I

GaAs •YEG0+ TMAs(y/~ ‘JO) AYEGO+AsI—1 3 (2/~~24) 0

DTMGO+AS~-~3(V,’~35)

L._..

102 1.00

1.05

1.10

1.15

1000/T

1.20

(

I .25

.30

K~)

Fig. 2. Growth efficiency (growth rate/group III molar flow rate) versus substrate temperature for GaAs using as reactants TEGa+AsH1 (s), TEGa+TMA (•) and TMGa+AsH5 (0).

changed, as seen in fig. 2. The major change was a drop-off in growth efficiency at substrate temperatures experiments below 525°C. The V/Ill ratio was 10 and for these (f(TEGa) = 18.8 p.mol/min f(TMA5) 188 ~.tmol/min). The effect may be due to the lower value of V/Ill ratio, but is probably due to the slower pyrolysis kinetics expected for TMAs relative to AsH 3. The small decrease in i~/f(TEGa) at higher temperatures is probably due to an increase in the kinetics of the parasitic reaction which depletes Ga from the gas stream. The surface morphology of GaAs grown using AsH3 was essentially featureless in the temperature range from 600 to 650°C,as seen in fig. 3a where interference contrast photographs of layers grown at 500, 550, 600 and 650°Care shown. At lower temperatures inefficient pyrolysis of AsH3 leaves Ga droplets on the surface. Using TMAs the best morphology was also obtained between 600 and 650°C. The most significant effect of replacing AsH3 =

by TMAs is a reduction of purity. Using AsH3, the values of carrier concentration, n, and3room and temperature p., are 3.2 x 1.iO’~cm 6548 cm2/V.mobility, s as shown in table Using TMAs the values are 5 X 1017 cm”3 and 2660 cm2/V. s. The value of room temperature electron mobility is plotted versus growth temperature in fig. 4. The best mobilities are obtained at 600°Cusing AsH3. Earlier studies indicated that temperatures higher than 600°C give higher impurity incorporation using TMGa + AsH3 [23,24]. The structural defects indicated by the poor morphology obtained at growth temperatures below 600°C, are undoubtedly responsible for the low mobilities obtamed in this temperature range. The increase in ionized impurity concentration is also reflected in the photoluminescence (PL) spectra. Using AsH3, room temperature PL half-widths of 34 meV have been measured. This is approximately the lower limit determined by thermal broadening [25,26]. Using TMAs, the half-widths are typically much broader, indicative of higher doping levels —

464

4

,

( . P. Auo

el at

0%! 1/’!. t~r(nt’11,of (ui/ni

a .—.-

—-—--—.

,—

_______

5

___

,Ij__

~ 4

500°C

1

,

550°C

600°C

‘fr

‘~

650°C

b

480 °C

I~rT H -1’550 °C

600 °C

650 °C

Fig. 3. Interference contrast microscope photographs of Ia) GaAs laser., gross n using I l( i I .\‘.l I .it and 6~ll’C and (hI InAs lasers gross ii using I F.ln + AsH at temperature.. of 4SF). 55)1, t~t)II and h~’II

teinper.iture.. ol SIll I, 551). t~(II)

C.P. Kuo et a!.

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465

OMVPE growth of GalnAs

.ATEGO#Ast-1

~

3 •YEG0’l-YMAS

_______________________

8 7

~GaAs -~TEGa#AsI-1

6

-

1TEG0#

> 90

-

E80

-

I

STMGa+A$t-~3

,V/IIt=24

YMAS, 2/~

‘JO

A

~7005-

: 4-

—

I

A -~

o

~

.

2-

.—~40o_.

.

• C

I

30

A -

p-type

—

2 t

~20I

500

550

LU

I

I

600

650

I 700

10

-

T(°C)

Fig. 4. 300 K electron mobility of GaAs versus growth temperature using TEGa+ AsH3 (~)and TEGa+TMAs (S).

[25,26]. At 550°C, narrow PL half-widths are obtamed even using TMAs. The reason is that both samples are p-type. Because of the higher valenceband density-of-states it requires higher doping levels to broaden the PL of p-type material [26]. The data are plotted versus growth temperature in fig. 5. Typical 77 K PL spectra for GaAs grown using TEGa and TMAs or AsH3 are labelled (a) and (b) respectively in fig. 6. Spectrum (a) shows a single, broad band edge peak indicative of a highly doped sample. Spectrum (b) shows a single, narrow band edge peak. The doping level is low and no acceptor peak is seen. For sample (c), grown using TMGa, a narrow band-edge peak is seen plus a peak at 1.480 eV- (837 nm) involving the acceptor carbon. The use of TMAs apparently provides no appreciable advantage over AsH3 for the growth of

I 550

I 600

I ~

I 650

I 700

Fig. 5. 300 K photoluminescence half-widths of GaAs versus growth temperature. Data are for TEGa+AsH3 (zs), TEGa+ TMAs (•) and TMGa+AsH3 (0). The samples were all n-type except those at 550°Cwhich were p-type, and the single sample grown using TMGa.

GaAs. The lower purity levels of commercially available (Alpha Products) TMAs currently represents a significant disadvantage. 3.2. InAs—TEIn

InAs was also grown using TEIn plus either AsH3 or TMAs. The molar flow rates of TEIn, AsH3 and TMAs were 5.42, 60 and 54.2 p.mol/min, respectively. The growth efficiency is plotted versus growth temperature in fig. 7. Between 550 and 650°C, the efficiency is between 1 x iO~and 2 X iO~p.m/mol, similar to the GaAs results. However, at lower temperatures the growth efficiency

Table 1 Properties of GaAs and GalnAs Material

Growth temperature (°C)

Thickness (gm)

Sources

GaAs

600

1.56

TEGa+AsH

GaAs GaAs Ga0471n053As Ga05ln05As

600 600 500 520

1.25 9.0 1.25 1.80

3 TEGa+TMAs TMGa+AsH3 TEGa+TEIn+AsH3 TMGa+TMIn+AsH3

300 K PL half-width (meV)

n (300 3)K)

34.3 78.0 31.4 68.0 53.0

3.2x10~ 5.0x 1017 p-Type Could not 17 contact 2.8x10

g (300 K) (cm2/V.s)

(cm 6548 2660 3363

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OMVPE growth of GaInA,s

lower )TEG

temperatures, below 550°C,as shown in fig. 3b.

~

Again, the use of TMAs yields no improvement

TEG:*A503

~

S

in growth efficiency. It apparently does not have the postulated effect [16] of blocking the parasitic reaction in this system.

-

(°) >-

3.3. GalnAs-TEGa

+ TEIn

z The alloy GaInAs was grown using triethylgroup III sources and AsH3 or TMAs. The growth

1-

z 0~

efficiency is plotted versus substrate temperature in fig. 8. The molar flow rates of TEIn, TEGa,

N.

I 790

I 600

I! 810

820

830

840

850

860

WAVELENGTH (nm)

Fig. 6. 77 K PL spectra for GaAs grown using TEGa+TMAs (a), TEGa+AsH3 (b) and TMGa+AsH3 (c). The intensity scale is 8 x larger for (a) than for (h) and (c).

sharply increases. Similar results have been re-

the GaAs AsH3 and 200and p. mol/min, and TMAs InAs were respectively. results, in thetherange As expected growth of 5,efficiency 4, from 1000 using AsH3 is seen to increase slightly as temperature decreases. More important is the effect of growth temperature on alloy composition. The most systematic method of comparing results is in terms of the distribution coefficient. Assuming the GaAs and InAs to be growing independently. ~

r5(InAs)

=

(1) ported by previous workers [27]. The effect is probably due to a decrease in the parasitic gasphase morphologies reactions at lower temperatures. Good could growth be obtained only at

r5(InAs) + ,~(GaAs)’ 650

600

I

I

5c) (550I

520

500

I

a

460

I

TI’C) 650

600

550

I I

500

o~

480

-

I

L!I~±~1~4”

E

IO~

:

A

A

E -~ C 0

!

•

A

N.

I0~

GO YEGO~A In AS •YEIS#

-

ATEIS+YEGOfrTMAS ~TMIn*

02 I 00

05

I I IC

J.~ I

I

IS

I

20

102 I

25

I

30

1000/1 ( K’( Fig. 7. Reaction efficiency (growth rate/In flow rate) versus growth temperature for OMVPE growth of InAs using TEIn +

AsH3

(A)

and TEIn+TMAs (•).

I 1.10

1.15

YMGO~ASH~J

I 120

1000/I

I 1.25

(

I I 30

K1)

Fig. 8. Growth efficiency versus temperature for GalnAs using TEIn + TEGa + AsH 3 (•), TEIn + TEGa + TMAs (A) and TMln+TMGa+AsH3 (0).

C.P. Kuo et a!.

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00

/

OMVPE growth of GalnAs

x kfln/fGa. (3) This x is the classical distribution coefficient. In general we can write x/(1 ~X)=k(fInfGa). (4)

[~~~OGA5

-

=

~~ ~0.7S

A

-

467

N.

I 0.50

-

0 25

-

I

A

A

5QQ

600

650

~ (CC) Fig. 9. In distribution coefficient versus temperature for GaInAs growth using TEIn+TEGa+AsH3 (Es) and TMIn+TMGa+ AsH3 (~)

____________ X

=

kifin +

where k

=

k2f~a

=

kf1~ kf1~+f~~’

(2)

k1/k2. As f1~approaches zero,

Thus, in fig. 9 we plot x/(1 — x) versus f1~/f04. Clearly, as T increases, k decreases with a sharp drop above 520°C using the triethyl-group III sources. This is qualitatively consistent with the growth efficiency versus temperature data presented in figs. 2 and 7. The effect of substituting TMAs for AsH3 is seen to be small, as expected from the minor effect TMAs has on growth rate for both GaAs and InAs. Obtaining good morphology GaInAs on InP substrates is somewhat of a problem. InP is known [25] to lose P at typical growth temperatures. A PH3 overpressure before the beginning of growth would suppress this, but would result in a transition layer of GaInAsP, not lattice matched to InP, at the beginning of the growth process. We simply used no PH3 overpressure and attempted to minimize the time the substrate was hot before begin-

)-

I a

b

c

d

Fig. 10. Interference contrast photomicrographs of Ga~— In5As surfaces grown using TEGa + TEIn + AsH3: (a) x = 0.485, T = 480°C, V/Ill = 32; (b) x = 0.52, T = 480°C,V/Ill = 64; (c) x = 0.515, T 500°C,V/Ill 96; (d) x = 0.5, T= 500°C,V/Ill = 144.

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OMVPE growth of GaInA.s

fling growth. Fortunately, the IR heating system allows rapid stabilization of the substrate temperature. Thus, the substrate was hot for less than I mm under AsH3 before the Ga and In flows were switched from the vent line to the reactor, The effect of V/Ill ratio on the resulting surface morphology at temperatures between 480 and 500°C is shown using high magnification interference contrast photomicrographs in fig. 10. For low values of V/Ill ratio (< 96) metallic drops are observed on the surface. For V/Ill ratios of 96 and 144 the major morphological defects are the cross-hatch related to the slight lattice mismatch between the GaInAs layer and InP substrate. The fine-scale roughness seen at low values of V/Ill ratio is known from work on InP and GaInP [19,20] to result in poor electrical and optical properties. The best values of PL intensity and _____________________________________

(b)

__________________ YEIn~As~3 b)YMGn~YMIn2AsI-1a~j

half-width for GaInAs were obtained for a V/Ill ratio of 96 and a substrate temperature of 500°C. The 77 K PL spectrum shown in fig. 11 shows a fairly broad (— 49 meV half-width) band edge emission peak and a large, 132 meV deep impurity related emission. In MBE and chloride VPE sampies a similar peak has been attributed to As vacancies [28]. Contacting these layers for electrical properties proved impossible, perhaps indicating a very high resistivity. 3.4.

GaInAs—TMGa + TMIn

A few experiments were performed using the trimethyl-group III sources. The growth efficiency for GaAs is considerably higher than using TEGa as seen in fig. 2. The value of > iO~p.m/moi indicates that no parasitic gas-phase reactions occur using TMGa. The growth efficiency is also high and temperature independent for GaInAs, as shown in fig. 8. The control of solid composition is consistent with this growth rate behavior. As seen in fig. 9, the In distribution coefficient is in the

a) TEGa+

~

(a)

4

10

\ I

N. N.

I

040

\(5)

I 400

1500

I 1600

WAVELENGTH

“-j-~--.-.. 1700

ss)

Fig. 11. 77 K PL spectra for Ga1 5In5As grown using (a) TEGa+TEIn+AsH3 and (b) TMGa+TMIn+AsH3.

range of 0.3—0.7 and is markedly less temperature dependent than for the ethyl-group III sources. GaAs grown using TMGa is well established to yield high quality material [18,23,24]. The narrow PL half-width measured at 300 K (— 31 meV) shown in fig. 5 is slightly smaller than the best obtained using TEGa, however, the sample is ptype. The 77 K PL spectrum shows, in addition to the band-edge emission peak at 1.502 eV (825 nm), a conduction band to C acceptor peak at 1.480 eV (837 nm). Thus, C acceptors are seen in GaAs grown using TMGa but not in that grown using TEGa. This is similar to the results reported by Bhat and Keramidas [12]. The OMVPE growth of high quality GalnAs using TMIn and TMGa has also recently been reported [21]. Perhaps because of problems during the initial stages of growth, discussed above, achieving excellent morphology for the GaInAs grown in our apparatus using TMGa and TMIn is difficult. Interference contrast photomicrographs of layers grown at different values of growth ternperature are shown in fig. 12. The best results are obtained at a growth temperature of 530°Cand a V/Ill ratio of 80. The surface morphology is

(P.

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OMVPE growth of GalnAs

-.. -

-

--

469

,::‘;.4

~

a

b

Fig. 12. Interference contrast photomicrographs of Ga V/Ill

=

80; (b) x

0.53, T= 533°C,V/Ill

=

80; (c) x

=

1 5In5 As grown using TMGa + TMIn + AsH3: (a) x = 0.50, T = 500°C, 0.53, T = 550°C,V/Ill = 100; (d) x = 0.50, T = 600°C.V/Ill = 60.

excellent and the PL intensity is found to be > 100 x more intense than that for material grown using triethyl-group III sources. A typical 77 K spectrum is shown as spectrum (c) in fig. 11. The spectrum shows a single, fairly narrow (— 27 meV half-width) peak plus a very weak impurity related peak. The half-width compares very favorably with the value of 35 meV reported by Duchernin et al. for Ga0471n053As grown by OMVPE [29] with approximately the same doping level. The apparent single peak may be due to the band—band transition and the conduction band to carbon acceptor transition combined, since C is only 13 rneV deep [29]. As listed in table 1, the best value of electron mobility obtained in the2/V. fews runs to datelevel is still at a doping of somewhat low, 3363 crn 3 x 1017 cm3. This compares fairly well with values of — 1800 cm2/V. s reported for Ga 046 In0 54As grown on GaAs [7] using TMGa + TEl + 2/V s reported for AsH3 and 3200 cm Ga 0481n052As grown on GaAs using TMGa + TMI + TMAs [30]. However, 2/V. it is far the s forbelow GaInAs 300 K mobility of 11,900 cm

grown on InP using TEGa + TEIn i- AsH3 by low pressure OMVPE [6].The major reason for the low mobility is the rather high background doping level. The residual donor comes from the TMIn. It may also be due to the small layer thickness. Fe diffusing from the InP substrate is known to severely limit the mobility of the GaInAs layers grown by MBE [31].

4. Summary This paper reports the OMVPE growth of GaAs, InAs and GaInAs in a horizontal, atmospheric pressure reactor. Using triethyl-group III sources yields good quality reactions GaAs, InAs and both GaInAs but parasitic gas-phase deplete Ga and In from the gas stream before reaching the substrate. This results in low values of growth efficiency (,~/f~)and lowgrowth values of In distribution coefficient. Bothinthe efficiency and distribution coefficient are temperature dependent. The substitution of TMAs AsH3 does improve the situation, but has for the adverse effectnot of

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C.P. Kuo eta!.

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OMVPE growth of GalnAs

introducing additional ionized impurities which lead to lower values of mobility and higher PL half-widths. Using trimethyl-group III sources eliminates all prereaction problems involving both Ga and In. The growth efficiency for both GaAs and GalnAs is significantly higher and growth rate and cornposition become much less dependent on temperature. The use of TMIn + TMGa gives much more intense PL (>100 x) for GaInAs, and the narrowest PL half-widths, indicative of high quality material.

References [I] H. Ohno and J. Barnard, in: GaInAsP Alloy Semiconductars, Ed. T.P. Pearsall (Wiley, New York, 1982) p. 437. - [2] Y. Matsushine and K. Sakai, ref. [1],p. 413. [3] J.D. Oliver and L.F. Eastman, J. Electron. Mater. 9 (1980) 693. [4] I-I. Ohno, C.E.C. Wood, L. Rathbun, DV. Morgan, G.W. Wicks and L.F. Eastman, J. AppI. Phys. 52 (1981) 4033. [5] ST. Jolly, S.Y. Narayan, i.P. Packowski and D. Capewell, SPIE Conf. Proc. 323 (1982) 74. [6] M. Razeghi, MA. Poisson, L.P. Larivan and J.P. Duchemm, J. Electron. Mater. 12 (1983) 371. [7] H.M. Manasivit and WI. Simpson, J. Electrochem. Soc. 120 (1973) 135. [8] B.J. Baliga and S.K. Ghandi, J. Electrochem. Soc. 122 (1976) 684. [9] J.P. Noad and A.J. SpringThorpe, J. Electron. Mater. 9 (1980) 601. [10] J.P. Duchemin, J.P. Hirtz, M. Razeghi and M. Bonnet, Inst. Phys. Conf. Ser. 63 (1981) 89. [11] J. Yoshino, J. Iwamoto and H. Kukimoto, J. Crystal Growth 55 (1981) 74. [12] R. Bhat and V.G. Keramidas, SPIE Conf. Proc. 323 (1982) 104.

[13] M. Oishi, and K. Kuroiwa, Japan. J. AppI. Phys. 21(1982) 203. [14] R.H. Moss and iS. Evans, J. Crystal Growth 55 (1981) [1511(W. Benz, H. Renz, J. Weidlein and M.H Pilkuhn, J. Electron. Mater. 10 (1981) 185. [16] C.B. Cooper, Mi. Ludowise, V. Aebi and R.L. Moon, J. Electron. Mater. 9 (1980) 299. [17] A.K. Chatterjee, MM. Faktor, R.J. Moss and E.A.D. White, J. Physique 43 (1982) C5-491. . [18] GB. Stringfellow, in: Semiconductors and Semimetals, Ed. W. Tsang, to be published. [19] C.C. Hsu, R.M. Cohen and GB. Stringfellow, J. Crystal Growth 63 (1983) 8. [20] C.C. Hsu, R.M. Cohen and GB. Stringfellow, J. Crystal Growth 62 (1983) 648. [21] M. Sacilotti, A. Mircea, R. Azoulay and K. Rao. Electronic Materials Conf., Burlington, VT, 1983, paper C-I. [22] H. Krautle, H. Roehle A. Escobosa and H. Beneking, J. Electron. Mater. 12 (1983) 215. [23] PD. Dapkus, H.M. Manasevit, K.L. Hess, T.S. Low and G.E. Stillman, J. Crystal Growth 55(1981)10. [24] T. Nakanisi, T. Udagawa, A. Tanaka and K. Kamei, J. Crystal Growth 55 (1981) 255. [25]G.H. Olsen and Ti. Zamerowski, Progr. Crystal Growth Characterization 2 (1979) 309. [26] GB. Stringfellow and H.T. Hall. Jr.. J. Electron. Mater. 8 (1979) 201. [27] T. Fukui and V. Horikoshi. Japan. J. AppI. Phys. 18 (1975) 2157. [28] K.H. Goetz, A.V. Solomonov, D. Bimberg, I-I. Jurgensen, M. Razeghi and J. Selders, J. Physique 43 (1982) C5-383. [29] J.P. Duchemin, J.P. Hirtz, M. Razeghi, M. Bonnet and S.D. Hersee, J. Crystal Growth 55 (1981) 64. [30] M.J. Ludowise, C.B. Cooper and R.R. Saxena, J. Electron. Mater. 10 (1981) 1051. [31] AS. Brown, S.C. Palmateer, G. Wicks, L.F. Eastman and C. Hitzman, Electronic Materials Conf., Burlington. VT, 1983, paper 1-4.