Growth of Ga1−xAlxSb and Ga1−xInxSb by organometallic chemical vapor deposition

400

Journal of Crystal Growth 77 (1986) 400—407 North-Holland, Amsterdam

GROWTh OF Ga1~A1~Sb AND Ga1~In~Sb BY ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION G.J. BOUGNOT, A.F. FOUCARAN, M. MARJAN, D. ETIENNE, J. BOUGNOT, F.M.H. DELANNOY and F.M. ROUMANILLE centre d’Electronique de Montpellier, Associs~au CNRS (UA 391), Université des Sciences et Techniques du Lan guedoc, Place E. Bataillon, F-34060 Montpellier Cedex, France

Organometallic chemical vapor deposition of Ga1 ~A1~Sb (x ~ 0.5) and for the first time Ga1 ~ln~Sb (x ~ 0.5) using trimethylgallium, trimethylantimony, trimethylaluminium and triethylindium has been obtained on GaSb and GaAs substrates. The experimental set and the growth conditions are detailed, On GaSb substrates, surface morphologies of Ga1 — Al~Sb epitaxial layers are satisfactory but Ga1 ~ layers exhibit a degradation of their X-ray diffraction spectra with increasing lattice mismatch. Solid compositions as functions of vapor phase compositions and growth temperatures are discussed on the basis of simple kinetic considerations.

I. Introduction

2. Experimental

Ga1 A1~Sb alloys are possible materials for optical fiber communications in the 1.3—1.55 ~.tm range [1—3].~ should be used in low field Gunn effect devices or in infrared light sources or detectors [4—6]for the wavelength range of the chalcogenide glass fibers, from 2.5 to 3.5 ~sm. But Ga1 ~In~As1 ~Sb~ lattice matched on GaSb or InAs substrates with the right energy band gap (0.2 ~ x ~ 0.45, 0.18 ~y ~ 0.40 from band gap calculations [7]) is plagued by a miscibility gap [8]. As reported by Cherng, Stringfellow and Cohen [9] for GaAs~~Sb~, OMCVD could be a good method for growing stable solid solutions in their miscibility gap. An alternative could be Ga4 5In~Sbwith intermediate graded layers on GaSh substrates. A few results for MBE and LPE of Ga1 ~In~Sb have been reported but none for OMCVD. In this paper, we present experimental results on Ga1~Al~Sb layers (x ~ 0.5) and on Ga1 ~In~Sb (x ~ 0.5) grown by atmospheric pressure OMCVD on GaSb and GaAs substrates.

The growth system is schematically represented in fig. 1. The reactor was a cooled wall vertical quartz tube, 5 cm ID and 45 cm long, with RF induction heating of a graphite vertical susceptor. Pd-diffused pure hydrogen flows through high purity trimethylgallium (TMGa), trimethylaluminium (TMA1) (Alpha Ventron), trimethylantimony (TMSb) and triethylindium (TEIn) (Société Maritime et Industrielle) bubblers. A 5% (diluted in H2) AsH3 line, diethylzinc (DEZn) and H2Se doping lines were also included. Additional hydrogen was introduced to achieve a total flow rate between 2 and 3.5 1/mm. All flow rates are controlled by electronic mass flow controllers. The substrates were n-type Te doped GaSb single crystalline wafers (100) and (111)B oriented, chemically polished with a 1% bromine—methanol solution. Polished semi-insulating (100) GaAs wafers were prepared by standard chemical etching (H2S04 : H202 H20:5:1 : 1). The temperatures were measured by a thermocouple inserted into the graphite susceptor and growth temperatures were corrected for cooling due to cold gas injection. Typical growth parameters are given into table 1.

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0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

G.J. Bougnot et al.

/

Growth of Ga

1 — ~A/~Sb and Ga1 — ,~Jn.~Sb by OMCVD

graphite / susceptor

u

____

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H20 probe

R.F. coil o 0 0

Va

c u urn

gauge

As

-cooling water

~

rap pump vent vent

+i”~RV

vent++++

LLLL

S -.

~TT

IMI

M

M

T E

lEt

I ~Pd

diffuser

I vent Fig. 1. Schematic diagram of OMCVD system.

• ,

AsH~

•

H2

___________ ___________

N2 Mass Flow

[..._—J

Controller

401

402

G.J. Bougnot et aL

/

Growth of Ga, - ~Al~Sb and Ga

1 _‘jn~Sbby OMCVD

Table 1 Growth parameters Growth parameters

Ga1 _~Al~Sb

Ga1

Total H2 flow rate (1/mm) TMGa source temperature (°C) TMGa partial pressure into the reactor (atm) TMAI source temperature (°C) TMAIsource TEIn partialtemperature pressure into (°C) the reactor (atm) TEIn partial pressure into the reactor (atm) TMSb source temperature (°C) TMSb partial pressure into the reactor (atm) Growth temperature (°C) V/total III partial pressure ratio

2—3 0 (0.5—1)x 10 ‘I 20 4 (0.5—0.05)x10

3, 5 0 (0.5—0.8)

—20 (1—2) xl 0-~ 640—680 PTMSB/(PTMAI

At the beginning of each run, the substrate temperature was raised to 400°Cunder H 2 flow, Then a TMSb partial pressure was maintained at its final value until the growth temperature was reached to prevent decomposition of the GaSb substrate. Finally, group III components were introduced into the reactor. The process was reversed at the end of the run. Figs. 2 and 3 illustrate the surface morphologies of Ga1 ~Al~Sb and Ga1 ~In~Sb layers as shown by optical microscopy. On GaSb substrates, hillocks with a two-fold symetry on (100) orientation and a three-fold symetry on (111) orientation are typically observed with a small surface density resulting 1VSb and in Gaa nearly mirror-like surface. Ga1 XA 1 ~In~Sb grown on GaAs substrates seem to be a mosaic with well oriented crystallites giving a poor morphology as expected from the huge lattice mismatch. Figs. 4 and 5 show scanning electron micrographs of cleaved cross-sections of Ga1 ~Al~Sb and Ga1 ~In,çSb epilayers on GaSb substrates. The layer thickness was determined by optical microscope observation on an as grown section when using GaAs substrates and after chemical revelation of the p—n junction when growing undoped p-type epitaxial ternary layers with AlSb or InSb content higher than 10 at% on ntGaSb substrates. Table 2 gives typical growth rate values for GaA1Sb and GaInSb layers. The composition of the ternary layers are determined by several methods: electron microprobe analysis, X-ray dif-

In ~Sb

>< iO~

30—60 (0.5—0,2)x 10 —20 0.9 x 10 500—700

+ ~TMGa)

=

1—2

‘~

PTMsS/(PTEIn + ~TMG~~)

=

0.2—0.9

fraction, optical absorption edge measurement of layers deposited on GaAs substrates.

3. Results and discussion 3.1. Ga

Al Sb ‘

V

The variation of the solid composition x,, at a growth temperature of 680°C with a constant V/Ill ratio of 2, as a function of the + ~TMGa) = x~,ratio in the range of 0—0.5 is reported in fig. 6. Compositions were measured on ternary layers grown in the same run on GaSb and GaAs substrates respectively by electron microprobe analysis and by optical absorption using the energy-band-gap—composition relationship from ref. [10]. The distribution coefficient k, i.e., the ratio x~to x~,is found to be approximately unity as already observed by Cooper et al. [11] on Ga1 ~Al~Sb and more generally on ternary Ill—V solid solutions where the substitution occurs on the group III sublattice [12]. It should be noticed that Cooper’s data were obtained at a different temperature (600°C)and on an InAs substrate. Our work confirms that solid composition does not depend on the nature of the substrate. But fig. 7 demonstrates that x~is temperature-dependent at constant x~in the range 640—680°C. Such a variation could be explained by kinetic considerations. ~TMAl/(~TMA

G.J. Bougnot ci al. / Grmlth of Ga, - ~A1, Sb

The solid composition x~is:

and Ga,

—

,In, ~hby OMC VD

403

(1)

where J~and ~Ga are the Al and Ga atom fluxes at the growing surface. A previous work [13] using the same experimental set, had shown that the

1 - ~AI~Sb epilayers: (a) on (100) GaSh substrate. .s = 0.10: (h) on (111)B GaSb substrate. = 0.08: (e) on (100) GaAs substrate. x = 0.036.

Fig. 3. Surface morpholog~of Ga1 - ,In ~Sh layers: (a)on (100) GaSh substrate. .~ = 0.11: (b) on (111)B GaSb substrate. x = 0.30; (c) on (100) GaAs substrate. x = 0.06.

.‘~

~~Al/(~AI

+J(;a),

Fig. 2. Surface morphology of Ga

404

G.J. Bougnot eta!.

/

Growth of Ga,

Fig. 4. Cleaved cross section of Ga GaSb; x

=

1 ~Al~Sb epilayer on (100) 0.12; magnification 160x.

,Al, Sb and Ga, ,In ,Sb l;t iJMCVD

[b

growth rate of GaSb versus temperature was constant for T> 600°C and thermally activated for T < 600°C with an activation energy ~ E1 of 41—42 kcal mol ~ Moreover, Ga species were controlling the growth kinetics. Here, we assume that the Al flux at the surface is thermally controlled with a thermal activation energy ~ E2, for 640 ~ T ~ 680°C. Furthermore, it is assumed that there is no interaction between Al and Ga gaseous species in

Table 2 Growth rates GaI~AlVSb

Ga1~In~Sb

H2 flow rate (1/mm) Total group III partial V/Ill pressure ratio (atm)

3

3.5

GroWth r:te(~im/min)

0n-o.07

b)

Hg. 5. (leaved Lross section of Ga1 ,ln~Sbepilayers: (a) on x(100) = 0.05, GaSb, magnification x 0.49, magnification SOOX. 160 x; (b) on (100) GaSb,

4 2x10 0.9

2iO~

~ For x varying from 0.07 to 0.17. for x varying from 0.03 to 0.47.

______-.

a)

h)

the ternary system. So, eq. (1) could be written: KAI exp( —~E 2/RT) XS KA) exp( —L~E2/RT)+ KG,, —

—

G.J. Bougnot et a!. / Growth of Ga, - aAlaSb and Ga

1 - alnaSb by OMCVD

X5

______________________________________

T680’C V

GaSb

Substrate

..

GaAs

Substrate

0.6

0

0.5

r

0.4

0/

.1

4 C

405

,

03

0.1

~

~

KcaI mole

~E2:43

C 0 C

2 ~ I, ~

0.2

2 S

0.01

0.1 /0

a

a/

0

0.1 0.2 0.3 0.4 0.5 Al/Ga +AI Partial pressure ratio

0.6

X5 1.05

Fig. 6. Mole fraction of AISb in Ga1 ..~Al~Sb epilayers as a function of Xv = ~TMAl /( ~TMAI + ~TMGa) with ~TMSb = 2 X iO~ atm,microprobe electron PTM5b/(PTMAI analysis; + PTMGa) (~)GaAs = 2:substrate, (U) GaSboptical substrate, absorption edge.

a

4~1.6,1O~

A\

Cb

1.06

1.07

1.08

1.09

~

[K~j

3/T with = PTMAJ/(PTMAI 0.1,a Fig. 7. Mole fraction of x~, AlSb in Ga1 — ~AlaSb+ PTMGa) epilayers= as function ~TMSb = 2 ofX 10 10 atm, ~TMSb/(PTMAI + PTMGa) = 2.

A

C

~-~7.3,1O~

x 1~O.O2 A

X1z0.195

X1.O

357

D

2e Fig. 8. X-ray diffraction pattern on Gai~lnaSb layers. A and B: Ka1 and Ka2 peaks of the substrate; C and D: Ka1 and Ka2 peaks of the layer.

406

/

G.J. Bougnot et aL

I

Tr550°C

2

U

0.3

V

Growth of Ga, _VA1VSb and Ga, - ~In VSb by OMCVD

T0600~C

KGa

/

—

C

~02

(2)

where the K ‘s are constants.1According eq. (2), is deducedtofrom fig. a7. .~E2 value of 43 kcal mo1 There is at this time no explanation for ~E 2 being nearly equal to ~E1.

/

•V Tr640’C Ta700’C

exp(—z.~E2/RT),

/

,

o C

2

‘0

3.2. Ga1

/

-

V~VSb.

/

U

I

o

/

‘

~

Ga1XInVSb It illustrates Fig. 8 shows the layers degradation X-ray deposited diffraction of oncrystalline GaSb results substrates. quality for

/

_________________________________ 0.4 0.2 0.3 ~TEln ~

~TMGa +~rEln

1~TMGa) with2 increasing at x = 0.357). lattice Themismatch dependence (asofhigh solidascorn2for X position ‘~TEln/(~TEIn + x,~ ~ 0.3 isx~on shownx~ in= fig. 9, for different temperatures. Compositions were determined from the

Fig. 9. Mole fraction of InSb in the Ga 1 ~In0Sb 4 atm. with and growth temperature 0.9 and PTM5b=10 Xv

~TMsb

/( ~TMGa

layers versus + ~TEi~)

=

optical absorption edge, the GaSb substrates being We did notinsucceed in drawing at transparent the absorption range the of thecurves ternary.

6 T= 550°C

/

/ /

5.

2

4

.

4,

‘C 0

2

0.1 0.2 0.3 Mole fraction of InSb in the solid

0.4

xs0.5

Fig. 10. Growth rate of Ga and ~TM5h —10 atm. 10In~Sbversus solid composition at constant growth temperature with

1’TMGa “TMSb/(

+

PTEIn) = 0.9

G.J. Bougnot ci a!.

/

Growth of Ga,~Al~SbandGa,~In~Sbby OMCVD

higher TEIn pressures because instable growth conditions due to TEIn condensation or decomposition into the gas line. So, in Ga1 ~In~Sb alloys it is observed that the x~versus x,,, curves move away from the k = 1 line with increasing temperature. This could be qualitatively explained like Ga1 ~A1~Sb. Chiang and Bedair [14] mdicated that the growth rate of InSb seems to lead to a constant value with raising growth temperature but their data was limited at T = 480°C by local melting of InSb substrates. We observed [13] that for T < 600°C, the growth rate of GaSb is thermally activated. So, in accordance with eq. (1) written for Ga1 ~In~Sb, the mole fraction of InSb in the ternary solid solution is expected to decrease with increasing temperature. Finally, we observe in fig. 10 that the growth rate of Ga1 ~In~ Sb increases with increasing InSb content in the layer at a constant growth temperature.

4.

Conclusions

OMCVD epitaxial growth of Ga1 ~Al~Sb has been achieved in the 0
407

Acknowledgements This work was partially supported by the “LCR Thomson—CSF”

and special thanks go to Dr.M.

Razeghi for fruitful discussions. The authors would also like to gratefully acknowledge the assistance of Dr. L. Martin for optical absorption determination, Dr. R. Fourcade for X-rays measurements and A. Rossi, C. Gril and L. Datas, from the “Laboratoire de Microscopie Electronique de l’Université de Montpellier” for scanning electron analysis and observations.

References [1] S.J.

Anderson, F. Scholl and J.S. Harris, in: Proc. North American Session of 6th Intern. Symp. on GaAs and Related Compounds, St. Louis, MO, 1976, Inst. Phys. Conf. Ser. 33b, Ed. L.F. Eastman (Inst. Phys., London—Bristol, 1977) p. 346 [2] H.D. Law, L.R. Tomasetta, K. Nakano and J.S. Harris, Appl. Phys. Letters 33 (5) (1978) 416 [3] R. Chin and C.N. Hill, AppI. Phys. Letters 40 (4) (1982) 332 [4] L.M. Dolginov, L.V. Druzhinina, P.G. Eliseev, IV. Krynkova, VI. Leskovitch, M.G. Mil’vidskii, B.N. Sverdby and E.G. Shevchenko, IEEE J. Quantum Electron. QE-13 (1977) 609 [51M. Poulain, M. Poulain and M. Matecki, Opto. 16 (1983) 13 [6] J.C. de Winter, M.A. Pollack, A.K. Srivastava and J.L. Zyskind, J. Electron. Mater. 14 (1985) 729 [7] F. Jia-Hua, Thesis, University of Montpellier 2 (1985) 18] K. Nakajima, K. Osainura, K. Yasuda and Y. Murakami, J. Crystal Growth 41(1977) 87 [9] M.J. G.B. Stringfellow and R.M. Cohen, AppI. Phys. Cherng, Letters 44 (1984) 677 10] C. Alibert, A. Joullié, A.M. Joullié and C. Ance, Phys. Rev. B27b (1983) 4946 [11] C.B. Cooper, R.R. Saxena and M.J. Ludowise, Electron. Letters 16 (1980) 892 [12] Stringfellow, J. Crystal Growth 62 (1983) 2225. [13] GB. A. Mebouah, Thesis, University of Montpellier (1985). [14] P.K. Chiang and SM. Bedair, J. Electrochem. Soc. 131 (1984) 2422