- Email: [email protected]
Characterization and growth of Al0.065Ga0.935Sb by liquid phase epitaxy
118
Journal of Crystal Growth 92 (1988) 118—122 North-Holland, Amsterdam
CHARACTERIZATION AND GROWTH OF AI0~5Ga0~5Sb BY LIQUID PHASE EPITAXY
S.C. CHEN, Y.K. SU and F.S. JUANG Institute of Electrical and Computer Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China Received 8 February 1988; manuscript received in final form 4 April 1988
AlQ()~5Ga0935Sbternary compound layers have been grown on GaSb substrates by liquid phase epitaxy using the supercooling technique. The optimum growth condition was determined to be a supercooling temperature of L~T 7°C for a cooling rate of 0.4 °C/min. The solid composition of an Al~Ga1_~Sbternary layer was obtained by EDS and EPMA to be x = 0.065. The band gap energy was 882 meV at 14 K and the temperature coefficient was —2.86 X iO~eV/K.
1. Infroduction Recently, antimonide-based compound semiconductors lattice-matched to GaSb substrates have been attracting more attention because of their direct energy band gap over a wide range from 1 eV (A1GaSb, wavelength 1.24 ~tm) [1,2] to 0.3 eV (InGaAsSb, wavelength 4.1 ~m) [3]. There are two alloy systems, A1GaSb and InGaAsSb, which are suitable for long wavelength lasers and photodetectors. The wavelength range from 1.3 to 1.6 ~tm is preferred for optical fiber communication because fibers have minimum absorption and dispersion in this range [4,5]. In optical fiber cornmunication, high quantum efficiency and high speed of fabricated avalanche photodiodes (APD) are desired. Since Ge-APD can only yield a poor signal-tonoise ratio due to the small ionization rate [6], there has been much study to develop avalanche photodiodes based on Ill—V compounds. It is well known that the signal-to-noise ratio of an APD depends on the ratio of electron and hole impact ionization coefficients (a and /3 respectively) [7]. If the spin—orbit splitting ~ is equal to the bandgap energy Eg we can obtain the maximum value of the a//3 = k ratio. In the Al~Ga1_~Sballoy system, the ratio k = a/$ varies with the cornposition value of x and the k value can be more than 20 as x is equal to 0.065 at room temperature
[8].Therefore, in Ill—V compound semiconductors A1GaSb is one of the candidates for avalanche photodiodes for the 1.3—1.6 ~tm range. So far few authors have studied A1GaSb with this composition value of x 0.065 [9]. In this paper, we will describe the liquid phase epitaxial fabrication procedure and the surface characteristics of A1GaSb layers. EDS (energy dispersive X-ray spectrometer) analysis was used to determine the composition of the A1GaSb layers. EPMA (electron probe micro analysis) was also used to investigate the atomic concentration profile of this ternary layer. The growth conditions, i.e. different supersaturation values from 2 to 120 C, were varied to obtain the optimum condition. The epitaxial layer thickness as a function of growth time, t, in the supercooling technique, was also measured. PL (photoluminescence) measurements were made to study its purity and energy gap.
2. Epitaxial growth The GaA1Sb ternary layer was grown on (100) oriented GASb n- or p-type substrates (MCP) by liquid phase epitaxy using the supercooling technique. The source materials were 7N Ga, 6N Sb and SN Al wire. The atomic compositions of the GaAlSb melt were X~1= 0.0018, X~a= 0.9800 and X~b= 0.0182 [10], the liquidus temperature being
0022-0248/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
S.C. Chen et al.
/
Characterization and growth ofAl
0065Ga0935Sb by LPE
119
464°C. Epitaxial layers were grown by means of the supercooling technique with 2 to 12°C supersaturation and a cooling rate of 0.4 °C/min. In order to obtain high purity ternary materials, the Ga melt was first baked under a Pd-purified H2 atmosphere at 800°C for 16 h, and then Al and Sb were added in the Ga melt and also baked at 800°C.Prior to loading the GaSb substrate in the graphite boat, the wafer cleaning processes were very important because of easy oxidation of the GaSb surface. The substrate was first cleaned in a series of organic solvents and the chemically etched in HF and hot HC1, respectively, for 5 mm, foltowed by rinsing in methanol. To reduce oxidation on the surface, contact of the GaSb wafer with air and water was avoided. The substrate was immersed in methanol and dried quickly then immediately loaded into the boat. A thermal cleaning was required to remove the thin residual oxide thin layer on the substrate at 580°Cfor 1 hr.
3. Results and discussion The supercooling technique provided a convenient method for growing LPE layers of urnformly and accurately controlled thickness. The epitaxial layer thickness is determined by staining the cleaved cross-section. The staining solution
loG
E -
to
~i~’~-
-
~~d~th/2 ox—
lot GROWTH TIME
t
(mm)
Fig. 1. Epitaxial alyer thickness d varying with time t for an Al0~5Ga0935Sb layer. Growth temperature 454°C, ~T= 7°C,cooling rate 0.4°C/mm and (100) orientation.
Fig. 2. Surface morphologies of an epiluxial layer grown with
(a)/1T=2°C,(b)L~T=7°Cand(c)L~T=12°C.
consists of 10 g FeCl3, 1000 ml H20 and 100 ml HC1 [11]. The cleaved cross-section is exposed to the etchant for 1 mm at room temperature and then the thickness of the epita.xial layer is easily measured by photomicrographs. Fig. 1 shows the relationship between thickness d and growth time t at a given uT = 7 C and cooling rate = 0.4°C/mm for an Al0065Ga0935Sb ternary layer. .
120
S.C. Chen et al.
Characterization and growth of Al
0 065Ga0 935Sb by LPE
EPILAYER
The exact solid compositions of the GaA1Sb ternary layers were also analyzed by EDS techrnque. Fig. 4 shows the EDS spectrum on the
_________________ , I _________, ______
surface mental compositions of aaof GaA1Sb of ternary the AlGaSb layer. The solid layer were and solid agreement 50% analyzed composition of with Sb toorder the respectively. be xmeasured results 3.25% is exactly of of Al, 0.065. EPMA 46.75% corresponding This measureof is Ga in properties ments. carried Photoluminescence out in an LPE-grown to (PL) investigate measurements ternary the layer, were deepitaxial mW termine filter, Ar-ion and the layers. laser band PbS Excitation (4880 photo-cell gap A) and through was was check supplied used an the interference as quality detector. byoptical a ele60 of The samples were atThe 14 K.ternary The thick-
Ga Sb
AlGa Sb
SUBSTRATE
Sb Go Al
/
—
.
-
-
10 Fig. 3. Distribution of gallium, aluminum and antimony of AlGaSb/GaSb determined by EPMA.
1/2. The thickness is nearly proportional to (time) Figs. 2a, 2b and 2c show SEM (scanning electron microscope) photographs of the surface morphologies of epitaxial layers grown with ~T equal to 2.7 and 12°C respectively. The surface morphologies of most epitaxial GaA1Sb layers grown in the range of ur = 4—10°Care smooth, similar to the one shown in fig. 2b, and the interface between the epitaxial layer and the GaSb substrate is also flat and free from inclusions. For epitaxial layers grown with ~T outside this range, the surface morphologies are fairly rough, as shown in figs. 2a and 2c. The EPMA technique is employed to locate the ternary layer—substrate interface position and to determine the solid composition of the epitaxial layer. The distribution of the elements for GaAlSb/GaSb is shown in fig. 3. The EPMA signal and cleaved cross-section SEM photographs of fig. 3 show that the layer—substrate interface is rather flat and the distribution of the elements for the GaAlSb ternary epitaxial layer is uniform. The composition of the ternary epitaxial layer is Al0 065Ga0935Sb.
ness The of thePLAlGaSb layersgrown was about tim. spectra epitaxial of the LPE ternary5 layers are shown in figs. 5a and Sb for different baking times. These are typical PL spectra of undoped AlGaSb and very similar to the results reported by Wada Woelketand Benzepitaxial for epitaxial GaSb [12] and by al. for GaAlSb [9]. The 14 K PL spectra consist of three emission bands in fig. S. The shortest wavelength peak located at 14060 A (882 meV) is the band-gap emission associated with free-electron to free-hole recombination. Since the compositional dependence of Al~Ga 1—x SB alloy direct energy gap Eg
__________
_________________________ Sb
Sb
—
~ Sb
Go
Al
Ga
10.7
kev Fig. 4. Spectrum of Al0 ~5Ga0935Sb layer measured by EDS. ENERGY
E,
S.C. Chen et al.
/
Characterization and growth of Al
0 065Ga0 935Sb by LPE
121
ENERGY leVi
ENERGY (eV) 0.9
a
0.8
0.9
114185
b
0.8
BAKING TIME 16
13160
13800
14440 WAVELENGTH (A)
15080
15720
13160
13800
14440 15080 WAVELENGTH I~)
15720
Fig. 5. 14 K PL peaks of A1GaSb layer with Ga melt baking time of (a) 8 h and (b) 16 h at 800°C.
on x can be 2represented [13] at 300 by K, EEg(x) = 0.726 + 1.129x + 0.368x 5 of GaAlSb is equal to 0.8 eV as x = 0.065 at 300 K., Eg of GaAlSb is equal to 0.8 eV as x = 0.065 at 300 K. The shift is —2.86 x 10-a eV/K and this shift is in good agreement with the value of —2.9 x 10-a eV/K obtained from GaSb stimulated emission wavelength by Ziel et al. [14] and somewhat smaller than the shift of —3.5 x i0~ eV/K reported by Casey and Panish for GaSb [iS] The middle wavelength 14185 A (874 meV) peak may be attributed to excitons bound to neu-
tral acceptors (BA) of carbon impurity [16]. The longer baking time of Ga melt was used and the lower intensity of the third 14580 A (850 meV) peak was obtained as shown in figs. Sa and Sb. The longest wavelength peak may be considered as BA transition of oxygen impurity as described by Wada et al. [9] The epitaxial layer quality depends on the degree of supersaturation, as shown in figs. 6a and 6b. The band—band transition spectrum (the shortest wavelength peak) for ~T = 7°C is stronger than that for ur = 2°C. According to the
ENERGY leVi os
—
ENERGY leVI
a
0.8
0.9
—
b
0.8
14(85
TEO4C/mu~TEo4C/m~
13160
13800
14440 15080 WAVELENGTH (~)
15720
13160
13800
14440 WAVELENGTH
15080
15720
1A1 Fig. 6. 14 K PL peaks of A1GaSb layer with ~ T of (a) 2°Cand (b) 7°C.The intensities are normalized to the same value.
122
S.C. Chen et al.
/
Characterization and growth ofAl
results of the Pt spectra as shown in figs. 5 and 6, the optimum degree of supersaturation is 7°Cand Ga melt baking time is 16 h at 800°C.
0045Ga ~935Sb by LPE
ported by the National Science Council, OC, under contract NSC-77-0608-E006-Oi.
References 4. Conclusions We have investigated the conditions of LPE growth for the Al0065Ga0935Sb ternary cornpound, using the supercooling technique with a cooling rate of 0.4°C/mn; the optimum degree of supersaturation was 7°C and Ga melt baking time was 16 h at 800°C. The elemental compositions of epitaxial AlGaSb, Ga = 46.75%, Al = 3.25% and Sb = 50%, were determined by EDS technique. The corresponding solid composition was exactly 0.065, which we wanted. The temperature coefficient of A10065Ga0935Sb was —2.86 X iO~eV/K and the band gap energy Eg was equal to 882 meV at 14 K
Acknowledgements The authors wish to express their thanks to Mr. F.C. Wu of the SEM laboratory for the SEM and EPMA measurements and Mr. C.Y. Nee and Mr. S.C. Lu of the Materials Research Laboratory Industrial Technology Institute, for the PL measurement. They would also like to express their deep gratitude to Dr. M.C. Wu for his continuous guidance and encouragement. This work was sup-
[1] KY. Cheng and G.L. Pearson, J. Electrochem. Soc. 124 (1975) 753. [2] H.D. Law, K. Nakano and L.R. Tomasetta, IEEE J. Quantum Electron. QE-15 (1979) 549. [3] and C. Caneau, AK. Srivastava, AG. Dentai, Zuskind MA. Pollack, Electron. Letters 13 (1986)J.L. 2119. 14] M. Horiguchi and H. Osansi, Electron Electron. Letters 12 (1976) 310. [5] T. Miya, Y. Terunuma, T. Hosaka and T. Miyashita, Electron. Letters 15 (1979) 106. [6] T. Kaneda, S. Kagawa, T. Mikawa, Y. Toyama and H. Audo, Appl. Phys. Letters 36 (1980) 572. [7] R.J. McIntyre, IEEE Trans. Electron Devices ED-13 (1966) 164. [8] 0. Hildebrand, W. Kuebart, K.W. Benz and M.H. Pilkuhn, IEEE J. Quantum Electron ED-17 (1981) 284. [9] T. Wada, K. Kubota and T.Ikoma, J. Crystal Growth 66 (1984) 493. [10] H.D. Law, K. Nakano and L.R. Tomasetta, IEEE J. Quantum Electron. EQ-17 (1981) 275. [11] A.K. Chin and WA. Bonner, Appl. Phys. Letters 40 (1982) 248. [12] C. Woelk and K.W. Benz, J. Crystal Growth 27 (1974) 177. [13] KY. Cheng, G.L. Pearson, R.S. Bauer and G.J. Chadi, Bull. Am. Phys. Soc. 21(1976) 365. [14] J.P. Ziel, R.J. Malik, J.F. Walker and R.M. Mikulyak, J. Quantum QE-32Heterostructure (1986) 1587. [15] IEEE H.C. Casey, Jr. andElectron. M.B. Panish, Lasers, Part B (Academic Press, London, 1978). [16] Y.K. Su, MC. Wu, K.Y. Cheng and C.Y. Chang, J. Crystal Growth 67 (1984) 477.
Journal of Crystal Growth 92 (1988) 118—122 North-Holland, Amsterdam
CHARACTERIZATION AND GROWTH OF AI0~5Ga0~5Sb BY LIQUID PHASE EPITAXY
S.C. CHEN, Y.K. SU and F.S. JUANG Institute of Electrical and Computer Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China Received 8 February 1988; manuscript received in final form 4 April 1988
AlQ()~5Ga0935Sbternary compound layers have been grown on GaSb substrates by liquid phase epitaxy using the supercooling technique. The optimum growth condition was determined to be a supercooling temperature of L~T 7°C for a cooling rate of 0.4 °C/min. The solid composition of an Al~Ga1_~Sbternary layer was obtained by EDS and EPMA to be x = 0.065. The band gap energy was 882 meV at 14 K and the temperature coefficient was —2.86 X iO~eV/K.
1. Infroduction Recently, antimonide-based compound semiconductors lattice-matched to GaSb substrates have been attracting more attention because of their direct energy band gap over a wide range from 1 eV (A1GaSb, wavelength 1.24 ~tm) [1,2] to 0.3 eV (InGaAsSb, wavelength 4.1 ~m) [3]. There are two alloy systems, A1GaSb and InGaAsSb, which are suitable for long wavelength lasers and photodetectors. The wavelength range from 1.3 to 1.6 ~tm is preferred for optical fiber communication because fibers have minimum absorption and dispersion in this range [4,5]. In optical fiber cornmunication, high quantum efficiency and high speed of fabricated avalanche photodiodes (APD) are desired. Since Ge-APD can only yield a poor signal-tonoise ratio due to the small ionization rate [6], there has been much study to develop avalanche photodiodes based on Ill—V compounds. It is well known that the signal-to-noise ratio of an APD depends on the ratio of electron and hole impact ionization coefficients (a and /3 respectively) [7]. If the spin—orbit splitting ~ is equal to the bandgap energy Eg we can obtain the maximum value of the a//3 = k ratio. In the Al~Ga1_~Sballoy system, the ratio k = a/$ varies with the cornposition value of x and the k value can be more than 20 as x is equal to 0.065 at room temperature
[8].Therefore, in Ill—V compound semiconductors A1GaSb is one of the candidates for avalanche photodiodes for the 1.3—1.6 ~tm range. So far few authors have studied A1GaSb with this composition value of x 0.065 [9]. In this paper, we will describe the liquid phase epitaxial fabrication procedure and the surface characteristics of A1GaSb layers. EDS (energy dispersive X-ray spectrometer) analysis was used to determine the composition of the A1GaSb layers. EPMA (electron probe micro analysis) was also used to investigate the atomic concentration profile of this ternary layer. The growth conditions, i.e. different supersaturation values from 2 to 120 C, were varied to obtain the optimum condition. The epitaxial layer thickness as a function of growth time, t, in the supercooling technique, was also measured. PL (photoluminescence) measurements were made to study its purity and energy gap.
2. Epitaxial growth The GaA1Sb ternary layer was grown on (100) oriented GASb n- or p-type substrates (MCP) by liquid phase epitaxy using the supercooling technique. The source materials were 7N Ga, 6N Sb and SN Al wire. The atomic compositions of the GaAlSb melt were X~1= 0.0018, X~a= 0.9800 and X~b= 0.0182 [10], the liquidus temperature being
0022-0248/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
S.C. Chen et al.
/
Characterization and growth ofAl
0065Ga0935Sb by LPE
119
464°C. Epitaxial layers were grown by means of the supercooling technique with 2 to 12°C supersaturation and a cooling rate of 0.4 °C/min. In order to obtain high purity ternary materials, the Ga melt was first baked under a Pd-purified H2 atmosphere at 800°C for 16 h, and then Al and Sb were added in the Ga melt and also baked at 800°C.Prior to loading the GaSb substrate in the graphite boat, the wafer cleaning processes were very important because of easy oxidation of the GaSb surface. The substrate was first cleaned in a series of organic solvents and the chemically etched in HF and hot HC1, respectively, for 5 mm, foltowed by rinsing in methanol. To reduce oxidation on the surface, contact of the GaSb wafer with air and water was avoided. The substrate was immersed in methanol and dried quickly then immediately loaded into the boat. A thermal cleaning was required to remove the thin residual oxide thin layer on the substrate at 580°Cfor 1 hr.
3. Results and discussion The supercooling technique provided a convenient method for growing LPE layers of urnformly and accurately controlled thickness. The epitaxial layer thickness is determined by staining the cleaved cross-section. The staining solution
loG
E -
to
~i~’~-
-
~~d~th/2 ox—
lot GROWTH TIME
t
(mm)
Fig. 1. Epitaxial alyer thickness d varying with time t for an Al0~5Ga0935Sb layer. Growth temperature 454°C, ~T= 7°C,cooling rate 0.4°C/mm and (100) orientation.
Fig. 2. Surface morphologies of an epiluxial layer grown with
(a)/1T=2°C,(b)L~T=7°Cand(c)L~T=12°C.
consists of 10 g FeCl3, 1000 ml H20 and 100 ml HC1 [11]. The cleaved cross-section is exposed to the etchant for 1 mm at room temperature and then the thickness of the epita.xial layer is easily measured by photomicrographs. Fig. 1 shows the relationship between thickness d and growth time t at a given uT = 7 C and cooling rate = 0.4°C/mm for an Al0065Ga0935Sb ternary layer. .
120
S.C. Chen et al.
Characterization and growth of Al
0 065Ga0 935Sb by LPE
EPILAYER
The exact solid compositions of the GaA1Sb ternary layers were also analyzed by EDS techrnque. Fig. 4 shows the EDS spectrum on the
_________________ , I _________, ______
surface mental compositions of aaof GaA1Sb of ternary the AlGaSb layer. The solid layer were and solid agreement 50% analyzed composition of with Sb toorder the respectively. be xmeasured results 3.25% is exactly of of Al, 0.065. EPMA 46.75% corresponding This measureof is Ga in properties ments. carried Photoluminescence out in an LPE-grown to (PL) investigate measurements ternary the layer, were deepitaxial mW termine filter, Ar-ion and the layers. laser band PbS Excitation (4880 photo-cell gap A) and through was was check supplied used an the interference as quality detector. byoptical a ele60 of The samples were atThe 14 K.ternary The thick-
Ga Sb
AlGa Sb
SUBSTRATE
Sb Go Al
/
—
.
-
-
10 Fig. 3. Distribution of gallium, aluminum and antimony of AlGaSb/GaSb determined by EPMA.
1/2. The thickness is nearly proportional to (time) Figs. 2a, 2b and 2c show SEM (scanning electron microscope) photographs of the surface morphologies of epitaxial layers grown with ~T equal to 2.7 and 12°C respectively. The surface morphologies of most epitaxial GaA1Sb layers grown in the range of ur = 4—10°Care smooth, similar to the one shown in fig. 2b, and the interface between the epitaxial layer and the GaSb substrate is also flat and free from inclusions. For epitaxial layers grown with ~T outside this range, the surface morphologies are fairly rough, as shown in figs. 2a and 2c. The EPMA technique is employed to locate the ternary layer—substrate interface position and to determine the solid composition of the epitaxial layer. The distribution of the elements for GaAlSb/GaSb is shown in fig. 3. The EPMA signal and cleaved cross-section SEM photographs of fig. 3 show that the layer—substrate interface is rather flat and the distribution of the elements for the GaAlSb ternary epitaxial layer is uniform. The composition of the ternary epitaxial layer is Al0 065Ga0935Sb.
ness The of thePLAlGaSb layersgrown was about tim. spectra epitaxial of the LPE ternary5 layers are shown in figs. 5a and Sb for different baking times. These are typical PL spectra of undoped AlGaSb and very similar to the results reported by Wada Woelketand Benzepitaxial for epitaxial GaSb [12] and by al. for GaAlSb [9]. The 14 K PL spectra consist of three emission bands in fig. S. The shortest wavelength peak located at 14060 A (882 meV) is the band-gap emission associated with free-electron to free-hole recombination. Since the compositional dependence of Al~Ga 1—x SB alloy direct energy gap Eg
__________
_________________________ Sb
Sb
—
~ Sb
Go
Al
Ga
10.7
kev Fig. 4. Spectrum of Al0 ~5Ga0935Sb layer measured by EDS. ENERGY
E,
S.C. Chen et al.
/
Characterization and growth of Al
0 065Ga0 935Sb by LPE
121
ENERGY leVi
ENERGY (eV) 0.9
a
0.8
0.9
114185
b
0.8
BAKING TIME 16
13160
13800
14440 WAVELENGTH (A)
15080
15720
13160
13800
14440 15080 WAVELENGTH I~)
15720
Fig. 5. 14 K PL peaks of A1GaSb layer with Ga melt baking time of (a) 8 h and (b) 16 h at 800°C.
on x can be 2represented [13] at 300 by K, EEg(x) = 0.726 + 1.129x + 0.368x 5 of GaAlSb is equal to 0.8 eV as x = 0.065 at 300 K., Eg of GaAlSb is equal to 0.8 eV as x = 0.065 at 300 K. The shift is —2.86 x 10-a eV/K and this shift is in good agreement with the value of —2.9 x 10-a eV/K obtained from GaSb stimulated emission wavelength by Ziel et al. [14] and somewhat smaller than the shift of —3.5 x i0~ eV/K reported by Casey and Panish for GaSb [iS] The middle wavelength 14185 A (874 meV) peak may be attributed to excitons bound to neu-
tral acceptors (BA) of carbon impurity [16]. The longer baking time of Ga melt was used and the lower intensity of the third 14580 A (850 meV) peak was obtained as shown in figs. Sa and Sb. The longest wavelength peak may be considered as BA transition of oxygen impurity as described by Wada et al. [9] The epitaxial layer quality depends on the degree of supersaturation, as shown in figs. 6a and 6b. The band—band transition spectrum (the shortest wavelength peak) for ~T = 7°C is stronger than that for ur = 2°C. According to the
ENERGY leVi os
—
ENERGY leVI
a
0.8
0.9
—
b
0.8
14(85
TEO4C/mu~TEo4C/m~
13160
13800
14440 15080 WAVELENGTH (~)
15720
13160
13800
14440 WAVELENGTH
15080
15720
1A1 Fig. 6. 14 K PL peaks of A1GaSb layer with ~ T of (a) 2°Cand (b) 7°C.The intensities are normalized to the same value.
122
S.C. Chen et al.
/
Characterization and growth ofAl
results of the Pt spectra as shown in figs. 5 and 6, the optimum degree of supersaturation is 7°Cand Ga melt baking time is 16 h at 800°C.
0045Ga ~935Sb by LPE
ported by the National Science Council, OC, under contract NSC-77-0608-E006-Oi.
References 4. Conclusions We have investigated the conditions of LPE growth for the Al0065Ga0935Sb ternary cornpound, using the supercooling technique with a cooling rate of 0.4°C/mn; the optimum degree of supersaturation was 7°C and Ga melt baking time was 16 h at 800°C. The elemental compositions of epitaxial AlGaSb, Ga = 46.75%, Al = 3.25% and Sb = 50%, were determined by EDS technique. The corresponding solid composition was exactly 0.065, which we wanted. The temperature coefficient of A10065Ga0935Sb was —2.86 X iO~eV/K and the band gap energy Eg was equal to 882 meV at 14 K
Acknowledgements The authors wish to express their thanks to Mr. F.C. Wu of the SEM laboratory for the SEM and EPMA measurements and Mr. C.Y. Nee and Mr. S.C. Lu of the Materials Research Laboratory Industrial Technology Institute, for the PL measurement. They would also like to express their deep gratitude to Dr. M.C. Wu for his continuous guidance and encouragement. This work was sup-
[1] KY. Cheng and G.L. Pearson, J. Electrochem. Soc. 124 (1975) 753. [2] H.D. Law, K. Nakano and L.R. Tomasetta, IEEE J. Quantum Electron. QE-15 (1979) 549. [3] and C. Caneau, AK. Srivastava, AG. Dentai, Zuskind MA. Pollack, Electron. Letters 13 (1986)J.L. 2119. 14] M. Horiguchi and H. Osansi, Electron Electron. Letters 12 (1976) 310. [5] T. Miya, Y. Terunuma, T. Hosaka and T. Miyashita, Electron. Letters 15 (1979) 106. [6] T. Kaneda, S. Kagawa, T. Mikawa, Y. Toyama and H. Audo, Appl. Phys. Letters 36 (1980) 572. [7] R.J. McIntyre, IEEE Trans. Electron Devices ED-13 (1966) 164. [8] 0. Hildebrand, W. Kuebart, K.W. Benz and M.H. Pilkuhn, IEEE J. Quantum Electron ED-17 (1981) 284. [9] T. Wada, K. Kubota and T.Ikoma, J. Crystal Growth 66 (1984) 493. [10] H.D. Law, K. Nakano and L.R. Tomasetta, IEEE J. Quantum Electron. EQ-17 (1981) 275. [11] A.K. Chin and WA. Bonner, Appl. Phys. Letters 40 (1982) 248. [12] C. Woelk and K.W. Benz, J. Crystal Growth 27 (1974) 177. [13] KY. Cheng, G.L. Pearson, R.S. Bauer and G.J. Chadi, Bull. Am. Phys. Soc. 21(1976) 365. [14] J.P. Ziel, R.J. Malik, J.F. Walker and R.M. Mikulyak, J. Quantum QE-32Heterostructure (1986) 1587. [15] IEEE H.C. Casey, Jr. andElectron. M.B. Panish, Lasers, Part B (Academic Press, London, 1978). [16] Y.K. Su, MC. Wu, K.Y. Cheng and C.Y. Chang, J. Crystal Growth 67 (1984) 477.