OMVPE growth of InAsSb using novel precursors

j. . . . . . . .

C R Y S T A L G R O W T H

ELSEVIER

Journal of Crystal Growth 156 (1995) 311-319

OMVPE growth of InAsSb using novel precursors K.T. Huang, Yu Hsu, R.M. Cohen, G.B. Stringfellow * Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112, USA Received 1 January 1995; manuscript received in final form 16 June 1995

Abstract InAs, InSb, InAsSb and the related bismuth containing alloys are useful materials for infrared applications. A significant effort has been expended to develop new group II! and group V precursors for organometallic vapor phase epitaxial (OMVPE) growth of these materials at low temperatures. We report the first use of a rarely studied group III source, triisopropylindium (TIPIn), together with the novel As and Sb precursors tertiarybutylarsine (TBAs) and tertiarybutyldimethylantimony (TBDMSb) for the growth of InAs and InAsSb epitaxial layers by atmospheric pressure OMVPE. InAs layers with good surface morphologies were obtained for growth temperatures as low as 300°C and low values of V / I I I ratio. Use of a high total flow rate and a reactor having a small volume upstream of the substrate alleviates the parasitic reaction problems reported earlier. This results in 3-5 x increase in the growth efficiency. Values of room temperature electron concentration, n, for InAs samples were found to range between 3 × 10 is cm -3 for layers grown at 300°C to 9 × 1016 cm -3 for layers grown at 400°C. These values of n are about an order of magnitude less than previously reported for InAs grown at the same temperature using either TMIn or EDMIn with AsH 3 or TBAs. InASl_xSbx (0 < x < 0.7) layers were grown at 350°C with excellent surface morphologies for low V / I I I ratios. The layers have free electron concentrations ranging from 9 X 1016 to 4 × 1017 cm -3. X-ray diffraction data and 10 K photoluminescence spectra indicate that both the InAs and InAsSb layers grown at low temperatures using the new precursor combination are far superior to layers grown using other precursors.

1. Introduction I n A s ~ _ x S b x has t h e lowest e n e r g y b a n d g a p r a n g e o f t h e c o m m o n I I I / V s e m i c o n d u c t o r alloys. H o w e v e r , even s m a l l e r b a n d g a p e n e r g i e s a r e r e q u i r e d for 8 to 12 # m i n f r a r e d d e t e c t o r a p p l i c a t i o n s . O n e a p p r o a c h to o b t a i n t h e s m a l l e r b a n d g a p e n e r g i e s r e q u i r e d is t h e a d d i t i o n o f a l a r g e g r o u p I I I e l e m e n t , such as T1 [1,2], o r a

* Corresponding author.

g r o u p V e l e m e n t , such as Bi [3-6], to I n A s S b . O u r p r e v i o u s w o r k u s e d b i s m u t h to d i l a t e t h e l a t t i c e c o n s t a n t in t h e s e alloys, with p r o m i s i n g results. H o w e v e r , t h e low g r o w t h t e m p e r a t u r e s o f 2 7 5 - 3 5 0 ° C r e q u i r e d to o b t a i n sufficiently high bismuth concentrations caused several problems: (1) inefficient pyrolysis o f t h e I n p r e c u r s o r t r i m e t h y l i n d i u m ( T M I n ) r e s u l t e d in low g r o w t h efficiency, (2) high r e s i d u a l c a r b o n i n c o r p o r a t i o n , a n d (3) p o o r p h o t o l u m i n e s c e n c e (PL) i n t e n s i t i e s [7,8]. T h e e a r l y O M V P E g r o w t h studies [7] u s e d t h e p r e c u r s o r s T M I n , ASH3, a n d t r i m e t h y l a n t i m o n y ( T M S b ) . T h e u s e o f novel In, A s , a n d Sb

0022-0248/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD! 0022-0248(95)00254-5

312

K.T. Huang et aL /Journal of Crystal Growth 156 (1995) 311-319

precursors offers the promise of improved epilayer quality for growth at low temperatures. The use of triisopropylindium (TIPIn) and arsine to grow InAs epilayers has been reported by Chen et al. [9]. TIPIn was found to pyrolyze at very low temperatures (50% pyrolysis at 115°C). Thus, the growth efficiency at temperatures between 275 and 350°C is not limited by the pyrolysis of the In precursor. However, parasitic reactions involving TIPIn resulted in low growth efficiencies in the mass-transport-limited regime [9]. The carbon contamination observed in the InAs layers was significantly smaller for TIPIn than for either TMIn or ethyldimethylindium (EDMIn). Tertiarybutylarsine (TBAs) is also an excellent precursor for low temperature growth. Pyrolysis is 50% complete at a temperature of 425°C as compared to 600°C for arsine [10]. Chen et al. [11] and Lum et al. [12] were the first groups to use it successfully for the growth of GaAs. The results of Watkins and Haacke [13] indicated that the carbon contamination in GaAs grown using TBAs is even lower than that in GaAs grown using arsine. Several new antimony precursors have been developed especially for low temperature growth [14-16]. A promising precursor for the low temperature O M V P E growth of InSb with low carbon contamination levels and good crystallographic quality is tertiary butyldimethylantimony (TBDMSb) [14]. In this work, we report improved quality for InAs and InAsSb layers grown at low temperatures using the precursor combination TIPIn, TBAs and TBDMSb. The properties of these layers are compared with those obtained previously using the conventional indium precursors. A comparison is also made with layers grown using TBAs and TBDMSb combined with TMIn or EDMIn.

2. Experimental procedure A horizontal, IR-heated, atmospheric-pressure O M V P E reactor was used for this study [17] having a rectangular cross section tapered from the entrance to the susceptor to avoid the forma-

tion of eddy currents and to minimize the volume. The group III and group V sources entered the reactor through separate tubes. The carrier gas was palladium-purified H 2 with a total flow rate as large as 4 { / m i n giving a flow velocity of 5.33 × 102 c m / m i n . These factors are expected to result in a reduction of the parasitic reactions observed earlier for O M V P E growth using TIPIn [9]. The group III precursors, TIPIn, TMIn or EDMIn, and the group V precursors, TBAs and TBDMSb, were kept in isothermal baths with both TMIn and E D M I n at 18°C, TIPIn and TBDMSb at 23°C, and TBAs at 5°C. The substrates were undoped (100) InAs and semi-insulating (100) GaAs. Before growth the substrates were degreased in 1 : 1 : 1 trichloroethane, acetone and methanol. The InAs substrates were then etched in 1:1 H F : H 2 0 for 4 min followed by 0.5% bromine in methanol for two rain. The GaAs substrates were etched in H 2 S O 4 for 3 min followed by 1 : 1 : 4 H 2 0 : H 2 0 2 : H 2 S O 4 for 4 min. After rinsing in deionized water the substrates were blown dry with nitrogen and immediately transferred into the reactor chamber. The surface morphologies of the epilayers were characterized using Nomarski differential interference contrast microscopy. Layer thicknesses, typically 0.8 to 1.1 ~m, were estimated by observing the heteroepitaxial interface between the epilayer and substrate on a cleaved cross section. The accuracy is approximately _+10% as estimated by comparison with higher resolution scanning electron microscope (SEM) measurements. The lattice constant and crystallinity were determined using a D I A N O XRD8000 X-ray diffractometer. The composition of the InAsSb layer was determined from Vegard's law assuming that the layers are elastically relaxed. Epilayers were grown on semi-insulating GaAs substrates for measurement of the electrical properties using the Van der Pauw technique. In contacts on four corners of the rectangular samples were annealed at 300°C for 3 min under N 2. A magnetic field of 5 kG and sample c/arrent of 1 0 / z A were used. A chopped Ar-ion laser, tuned to a wavelength of either 4880 or 5145 A, was used to excite the PL (power intensity = 40 o

IK T. Huang et al./Journal of Crystal Growth 156 (1995) 311-319 Temperature

6000" 10~=

o

...= •~

313

600

500

]

]

(°C) 300

400 T

T

A

5000

TMIn+AsH3+TMBi(Maet a1.[17](1991)) TIPIn+AsH3(Chertet al,[9] (1993)) TIPIn+TBAs(presentwork) -~

4000

30oo

104

txJ

=

I0 ~

2 2000

2

Total Flow

3

4

Rate (liter/min)

Fig, 1. Growth efficiency for InAs grown using TIPIn and TBAs versus total flow rate for a growth temperature of 350°C.

W / c m 2) for s a m p l e s h e l d at 10 K. T h e P L was c o l l e c t e d by an off-axis p a r a b o l o i d a l m i r r o r a n d f o c u s e d o n t o t h e e n t r a n c e slit o f a S P E X M500, 0.5m, f4 s p e c t r o m e t e r . A c o o l e d I n S b o r H g C d T e d e t e c t o r was p o s i t i o n e d close to t h e exit slit.

3. Results and discussion 3.1. I n A s growth G o o d quality I n A s was p r e v i o u s l y o b t a i n e d using T I P I n a n d A s H 3 even at very low g r o w t h

10 1.0

1.2

1.4

1.6

1.8

2.0

1000/Tg ( l / K )

Fig. 2. Growth efficiency for InAs grown using TIPIn and TBAs as a function of temperature with a total flow rate of 4 C/min. The results for InAs grown using TMIn or TIPIn with AsH 3 from Chen et al. [9] and Ma [17] are also shown for comparison.

t e m p e r a t u r e s [9]. H o w e v e r , p a r a s i t i c r e a c t i o n s res u l t e d in g r o w t h efficiencies a p p r o x i m a t e l y 10 × l o w e r t h a n o b s e r v e d for T M I n a n d E D M I n in t h e m a s s - t r a n s p o r t - l i m i t e d r e g i m e at t e m p e r a t u r e s o f 400°C a n d higher. T o alleviate this p r o b l e m a n e w r e a c t o r g e o m e t r y a n d h i g h e r t o t a l flow r a t e s w e r e used. Fig. 1 shows t h e i n c r e a s e in g r o w t h efficiency with i n c r e a s i n g t o t a l flow r a t e for a s u b s t r a t e t e m p e r a t u r e o f 350°C.

I

!

20 g m

Tg = V/III

4 0 0 °C = 6.27

Tg = 3 5 0 °C V/III = 4.67

Tg = V/III

325 °C = 2.81

Tg = 300 °C V/III = 2.21 ~

Fig. 3. Surface morphologies of InAs layers grown at several temperatures and V/III ratios.

K.T. Huang et al. /Journal of Crystal Growth 156 (1995) 311-319

314

Fig. 2 shows the growth efficiency as a function of temperature for comparison with the earlier results obtained by Chen et al. [9] using TIPIn as well as the earlier results obtained using T M I n and EDMIn. The growth efficiency for InAs grown using TIPIn has been increased by as much as 5 × using the higher flow velocity and new reactor geometry. This is extremely important for O M V P E growth since it represents both a 5 × shorter run time, which can be significant for the growth of thick layers, and much less waste of the expensive organometallic precursors. The growth efficiency using TIPIn is now 10 × higher than obtained for T M I n for growth at 300°C. The temperature independence of the growth efficiency indicates that even at 300°C growth occurs in the mass-transport-limited regime, i.e., the TIPIn is completely pyrolyzed. This is not surprising considering that the value of Ts0 is 115°C for TIPIn [9]. Some parasitic reactions apparently still occur, as evidenced by the 2 × lower growth efficiency for T I P I n than for TMIn in the mass-transport-limited growth regime. Fig. 3 shows Nomarski photographs of the best surface morphologies for InAs obtained at growth temperatures between 300 and 400°C as well as the V / I I I ratios used. The best morphology at Temperature (°C) ~.

102'~

~

10~"

600 500 400 1 L , O TMInor EDMIn÷AsH3(Mael aL[17]0991)) [ • TIpIn+AsH3(Cheneta|.[9](1993)) A TIPIn+TBAs(Presentwork)

300

]O

o!

10 ~

8 o

10tT! 10~+. 1.0

t 1.2

1.4

1.6

1.8

2.0

1000frg (l/K) Fig. 4. R o o m t e m p e r a t u r e electron concentration versus growth t e m p e r a t u r e for InAs layers grown using TIPIn and TBAs. T h e results for InAs grown using TMIn, E D M I n , and T I P I n for several growth temperatures from C h e n et al. [9] and M a [17] are also shown for comparison.

E n e r g y (meV) 450 400 350

E n e r g y (meV) 450 400 350

""t.

kY

py I

~TIPIn+TBAs

rxY 2.6 z8 3.o 3.2 3.4 3.6 3.8

2.6 2.8 3.0 3,2 3.4 3.6 3.8

Wavelength (IJm)

W a v e l e n g t h (llm)

Fig. 5. 10 K photoluminescence spectra for InAs grown at (a) 400°C and (b) 350°C using T M I n , E D M I n , or TIPIn with TBAs.

300°C was obtained using a V / I I I ratio of 2.21 as compared with a value of 461 for the combination of TIPIn and AsH 3 at the same temperature [9]. This is because TBAs decomposes much more efficiently than AsH 3 at low temperatures. All undoped epilayers are n-type. Fig. 4 shows the room temperature electron concentration plotted versus growth temperature. The results for InAs grown using T M I n and E D M I n [17] and earlier results for TIPIn with AsH 3 [9] are included for comparison. The electron concentration is independent of the group V source for growth using TIPIn. The electron concentrations measured for low growth temperatures using TIPIn are much smaller than those obtained using TMIn or EDMIn. The donor impurity for layers grown using TIPIn was determined previously to be carbon [9]. The similarity in behavior for the present data suggests that the donor is also carbon, although no mass spectroscopy measurements were performed for verification. The 10 K PL results for InAs layers grown at 400 and 350°C with various group III sources are shown in Figs. 5a and 5b. The peaks observed near 3.0/xm are due to band-to-band and exciton recombination [7,18] and the peaks located near

K.T. Huang et al. /Journal of Crystal Growth 156 (1995) 311-319

3.08 and 3.25 ]zm are due to emission processes involving either impurity or defect states [19]. It is clearly seen that the intensity ratio of band edge to impurity emission decreases with decreasing growth temperature, as observed previously for InAs layers grown using T M I n and arsine [20]. Both the P L intensities and the ratio of band edge to impurity emission follow the trend: TIPIn > E D M I n > T M I n for InAs growth at 400°C and TIPIn > E D M I n > TMIn at 350°C. For growth temperatures of 350°C and lower the PL in samples grown using T M I n and arsine is too weak to be detected. The intensity for InAs grown using TIPIn is apparently still slightly superior to that for layers grown using EDMIn, although the difference may not exceed the experimental uncertainty. Fig. 6 compares the 10 K P L spectra for InAs samples grown using TIPIn and TBAs at temperatures between 300 and 400°C, including the P L spectrum from an InAs substrate. The PL intensities are similar for the sample grown at 400°C Energy (meV) 400

450

"~

~

~

350

Tg = 350 °C

oc

~

subsfrate

2.6 2.8 3.0 3.2 3.4 3.6 3.8

W a v e l e n g t h (gin) Fig. 6. 10 K photoluminescence spectra for three samples of InAs grown with TIPIn and TBAs at growth temperatures of 400, 350 and 300°C. The 10 K PL spectrum of an InAs substrate is also shown for comparison.

315

100"

2

0

0 0

lO~

AA~ 0 O TMIn+AsH3(Fangetal.[20](1990)) TIPht+TBAs(Presentwork)

.1

200

3~0

4~0

5~0

6~0

700

T8 (°C) Fig. 7. 10 K PL intensity versus growth temperature for InAs layers grown using TIPIn + TBAs. The results are compared with those of Fang et al. [7].

and the InAs substrate, indicating that good quality InAs epilayers can be obtained with growth temperatures of 400°C and higher. For samples grown at lower temperatures, the electron concentration increase coincides with an increase in the intensity of the impurity emission relative to the band edge emission. The PL intensity also decreases, as shown in Fig. 7. The data for InAs grown using TIPIn and TBAs shows the same trend reported earlier by Fang et al. [4,7] for layers grown using TMIn and arsine. No PL was observed for samples grown using TMIn + AsH 3 at temperatures below 350°C [7]. The PL intensities for the samples grown using TIPIn + TBAs are consistently higher than those grown using TMIn and AsH 3 and PL is detected for the first time for samples grown at temperatures as low as 300°C.

3.2. InAsSb growth For the growth of InASl_xSb x (0 < x <0.7) layers a temperature of 350°C was chosen, based on a previous study indicating that good quality layers can be grown at this temperature with the possibility of significant Bi incorporation [6]. Fig. 8 shows the (400) X-ray diffraction scans and the corresponding interference contrast micrographs for four samples with Sb concentrations between x = 0.20 and 0.66. The epilayers were grown directly on the InAs substrates with no graded layers. For the layer with the lowest Sb concen-

316

K.T. Huang et al. /Journal of Crystal Growth 156 (1995) 311-319 InAs

// //

I n A s o . 8 ~

InAso.64Sbo.36

"a

InAso.soSbo.5o

Jl

M i

InAso.34Sbo.66

L...--.--A

58

60

20~m

62

Fig. 8. X-ray diffraction scans and Nomarski interference contrast micrographs for a series of InAsl_xSbx samples grown at a temperature of 350°C.

tration the lattice mismatch between epilayer and substrate is small. This results in sharp X-ray peaks with a resolved K a l and K a 2 doublet, indicating good crystallinity. With increasing Sb concentration the X-ray peaks are broadened, probably due to the lattice mismatch with the substrate, and the K a l and K a 2 peaks can no longer be resolved. Typically, for x < 0.4, cross hatch morphologies are observed. Value of x > 0.4 (Aa/a >0.027) results in orange-peel-like morphologies. Qualitatively, the X-ray peak intensities for the epilayers grown using TIPIn + TBAs + TBDMSb are stronger and narrower than for layers grown with the conventional precursors, indicating that layers with better crystallographic quality can be obtained. A summary of the growth parameters for the samples shown in Fig. 8 is given in Table 1. The V / I I I ratios are less than 6 and the ratio of the antimony to group V concentration in the solid is nearly the same as that in the vapor indicating that the Sb distribution coefficient at 350°C is nearly unity. The solid composition is plotted versus the ratio of input Sb to As + Sb in the vapor for various group III and group V precursors in Fig. 9. The data of Fukui and Horikoshi [21], obtained at 500°C, are accurately described by a thermodynamic calculation [22] assuming equilibrium at the interface, indicated by the solid line. The data obtained for growth at 350°C using TIPIn, TBAs, and TBDMSb with a V / I I I ratio of between 4 and 6 results in an increased Sb incorporation. This may be partially due to the low value of actual V / I I I ratio. Since neither TBAs nor TBDMSb pyrolysis is likely to be complete at 350°C, the real V / I I I ratio at the inter-

Table 1 Parameters for the OMVPE growth of InAsa_xSbx at 350~C Sample No. IAS#35 IAS#54 IAS#19 IAS#18

Composition

Lattice constant

Thickness

Molar flow rate (~mol/min)

.xsb

a (-~)

(/zm)

TIPIn

TBAs

TBDMSb

Sb (As + Sb)

Input V / I I I ratio

0.20 0.36 0.50 0.66

6.143 6.210 6.269 6.336

0.80 0.75 0.80 0.80

3.015 3.015 3.015 3.015

13.172 10.512 7.206 4.362

4.628 6.719 7.652 8.858

0.260 0.390 0.515 0.670

5.904 5.715 4.928 4.385

I<2T. Huanget aL/Journal of Crystal Growth156 (1995)311-319 face is probably even smaller than 4. Thermodynamic calculations indicate that the Sb distribution coefficient should be unity for V / I I I = 1 [23]. An additional factor is the difference in pyrolysis rate between TBAs and TBDMSb. The values of Ts0 for these two precursors are reported to be 380-425°C for TBAs [24] and 300°C for T B D M S b [25]. This would also result in an increase in the ratio of Sb to As incorporated into the solid. T h e data obtained for the combination of E D M I n , TBAs, and T B D M S b [26] obtained at very high values of V / I I I ratio indicate that while both factors are significarlt, the m o r e rapid pyrolysis of T B D M S b relative to TBAs plays the larger role. An additional factor is the increasing importance of surface kinetic processes, relative to thermodynamics, as the growth t e m p e r a t u r e is decreased. This may involve kinetic processes in addition to those discussed above, although our understanding of the kinetics of the growth process is so primitive that it is impossible to gain additional insight into the processes controlling the antimony distribution coefficient. T h e background electron concentrations measured at room t e m p e r a t u r e for InAs~_~Sb~ are

1.0

10 ~ o~

0.8]

./" [

,""//'"ooOOOl "'":~

0.6 -

"'A

x~ 0.4

I

V/Ill = I

/"

.~ oo /'a 0

O°

OO

[]

OO

"'"AS

/

]

/

7

0.2

0.0 0.0

0.2

0.4

0.6

0.8

1.0

Fig. 9. S o l i d v e r s u s v a p o r c o m p o s i t i o n f o r I n A s l _ x S b x g r o w n u s i n g s e v e r a l g r o u p I I I a n d V p r e c u r s o r s . T h e solid l i n e w a s calculated using the DLP model, assuming equilibrium at the i n t e r f a c e [22]. T h e s q u a r e d a t a p o i n t s (1~) a r e f r o m t h e w o r k

of Fukui and Horikoshi [21].

I O EDMIn+TBAs+TBDMSb,Tg=350*C(Huanget a1.[26](1994)) • EDMIn+TBAs+TBDMSb+TMBi, Tg-~350oC(Huanget aL[6](1994)) • TIPIn+TBAs+TBDMSb,Tg=350°C(Presentwork)

| ~ 10 ~ O

S •

AA A

0%

o

k~AA •

•

• Ak, ,I,

10~6/ 0.0

012

014

016

Composition

018

1.0

x

Fig. 10. Room temperature electron concentration versus solid composition for InAsl_xSb x layers grown using TIPIn, TBAs, and TBDMSb at 350°C. The data are compared with Huang et al. [6,26].

shown as a function of solid composition in Fig. 10. The donor in InAsSb grown using T M I n and E D M I n has been identified as carbon, presumably coming from the methyl radicals on the group I I I source molecules [24]. Clearly the donor concentration due to carbon contamination is approximately 3 - 5 times lower when T I P I n is substituted for E D M I n , presumably due to the reduction in the concentration of methyl radicals on the surface. The carbon concentration was not measured directly, but it is likely less than or equal to the free electron concentration. The carbon contamination level is seen to decrease as the Sb content of the solid increases. This may be due to a decrease in the group V to C bond strength. The S b - C bond is much weaker than the A s - C bond. Fig. 11 shows the 10 K PL spectra of InAs0.sSb0.2, InAs0.64Sb0.36 and InAs0.s3Sb0.47 grown at 350°C. The PL spectrum for the sample with x = 0.2 has a dip at 4.3 /zm caused by C O z absorption. As expected for x < 0.65, the PL curves shift to longer wavelength as x is increased [6]. Because the lattice mismatch between the epilayer and substrate (InAs) increases with increasing x, an increase in non-radiative defects is expected. This would result in a decrease in the minority carrier lifetime of the

~ TIPln÷TBAs*TBDMffO'Tg-~'50~C'4
317

K.T. Huang et aL /Journal of Crystal Growth 156 (1995) 311-319

318

Energy (meV)

3.5

300

250

200

150

I

I

I

I

4.5

5.5

6.5

7.5

8.5

9.5

10.5

Wavelength (~tm) Fig. 11. 10 K photoluminescence spectra for three samples of InAsl_xSbx, x = 0.2, 0.36, 0.47, grown at 350°C using TIPIn, TBAs, and TBDMSb.

InAsSb and a consequent decrease in the P L intensity. Nevertheless, this is the first time that PL has b e e n intense enough to measure for InAsl_xSb x, with x = 0.5, grown at 350°C. This is indicative of the improved quality of the InAsSb layers grown at 350°C using TIPIn, TBAs, and TBDMSb.

4. Conclusions Epitaxial layers of InAs and InAsSb have b e e n grown at low t e m p e r a t u r e s using a combination of novel precursors: TIPIn, TBAs, and TBDMSb. This is the first time InAs and InAsSb have b e e n grown using these precursors. Although parasitic reactions between T I P I n and TBAs cannot be avoided entirely, the use of a reactor with a small volume u p s t r e a m of the substrate with tapered walls to avoid eddy currents and a large total flow rate has b e e n shown to result in a significant increase in the growth efficiency. This makes T I P I n a good candidate precursor for replacing T M I n and E D M I n for O M V P E growth at low temperatures, since T I P I n pyrolyzes at much lower temperatures. G o o d InAs and InAsSb sur-

face morphologies were obtained at temperatures as low as 350°C with low V / I I I ratios. Moreover, X-ray results indicate good crystallinity for the InAs and InAsSb layers. For InAs, the free electron concentrations in layers grown at 350°C or lower using T I P I n are about one order of magnitude lower than for layers grown using T M I n or E D M I n . The free electron concentration is found to decrease as x increases. Strong 10 K PL was observed for InAs grown at temperatures from 300 to 400°C. The PL intensities for materials grown using several In precursors along with TBAs are ranked in the order: T I P I n > E D M I n > TMIn. PL was observed for InAsl_xSbx with x values over a broad range. For the first time PL was observed for material with x = 0.5 for growth at 350°C. These results improve the outlook for low t e m p e r a t u r e O M V P E growth of In-containing I I I / V compounds and alloys using TIPIn. The ease of pyrolysis and reduced carbon contamination levels, as comp a r e d with T M I n and E D M I n , suggest that T I P I n may be even more useful for CBE and low pressure O M V P E growth.

Acknowledgements The authors would like to thank Office of Naval Research for financial support of this work.

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