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Influence of ultrasound on the growth striations and electrophysical properties of GaxIn1−xSb single crystals
Solid-State Electronics 51 (2007) 820–822 www.elsevier.com/locate/sse
Letter
Influence of ultrasound on the growth striations and electrophysical properties of GaxIn1xSb single crystals G.N. Kozhemyakin a
a,*
, L.V. Zolkina a, M.A. Rom
b
Laboratory of Crystal Growth, The V. Dal Eastern Ukrainian National University, Bl. Molodezhniy, 20 A, Lugansk 91034, Ukraine b Institute for Single Crystals, National Academy of Science of Ukraine, 60 Lenin Street, Kharkiv 61001, Ukraine Received 5 September 2006; received in revised form 30 April 2007; accepted 9 May 2007
The review of this paper was arranged by Prof. Y. Arakawa
Abstract Effect of ultrasonic waves on growth striations and electrophysical properties of GaxIn1xSb single crystals with x up to 0.03 have been investigated. A decrease in the ultrasound field of growth striations in GaxIn1xSb single crystals has been observed. The carrier concentration and thermal emf in these crystals were larger than that in crystals pulled without ultrasound. 2007 Elsevier Ltd. All rights reserved. PACS: 150.100 Compound semiconductors Keywords: Solid solutions; Czochralski method; Growth from melt; GaInSb single crystal; Semiconducting ternary compounds
GaxIn1xSb single crystals with a band gap from 0.73 to 0.17 eV are of great interest for optoelectronic devices, because their wavelength can be varied in the range of 1.7–7 lm, depending on the composition [1,2]. However, such problems as polycrystalline growth, axial and radial compositional inhomogeneities etc., are inherent to growth of GaxIn1xSb crystals [3,4]. Therefore, a lot of work was dedicated to the growth process of GaxIn1xSb single crystals [5–9]. Recently, Tsaur et al. [9] grew GaxIn1xSb single crystals with InSb concentrations up to 23 mol% using the conventional Czochralski process. It was reported that pulled crystals had significant axial and radial segregation of InSb [8]. To reduce the components’ inhomogeneity in the single crystals, Czochralski method with ultrasound field can be employed [10]. The ultrasound at a frequency of about 1 MHz influenced the growth process positively by eliminating the striations in GaAs crystals, Bi–Sb single
*
Corresponding author. Tel.: +380 642 917 924; fax: +380 642 413 160. E-mail address: [email protected] (G.N. Kozhemyakin).
0038-1101/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.sse.2007.05.002
crystals with constant diameter and in the facet region of InSb single crystals [10–12]. Originally, growth of GaxIn1xSb crystals in ultrasound field was investigated by Hayakawa [13–15]. Experiments showed that the application of ultrasound at a frequency of 10 kHz and power up to 120 W did not provide high quality single crystals due to the melt cavitations and flow patterns with high speed [13–15]. This article describes the growth of GaxIn1xSb single crystals with x up to 0.03 under megahertz range ultrasound, investigation of the growth striations in the pulled single crystals and the results of the measurements of carrier concentration and mobility, electrical resistivity and thermal emf in pulled crystals. GaxIn1xSb single crystals were grown by a modified Czochralski method using InSb seed single crystals in the h1 1 1iB direction. The melt mass did not exceed 80 g. The pulling and rotation rates of the crystals were 3 mm/h and from 1 to 10 rpm, respectively. A fused silica crucible of 40 ID and 30 mm height was not rotated. Ga, In and Sb of 6 N were used as source materials. The crystals were
G.N. Kozhemyakin et al. / Solid-State Electronics 51 (2007) 820–822
pulled in high purity Ar. Ultrasound at frequencies of 0.72 and 1.44 MHz was introduced into the melt from a piezotransducer through a fused silica waveguide, with 10 mm diameter and 300 mm length, fused to the bottom of silica crucible. The direction of ultrasonic waves was parallel to the pulling axis. Grown GaxIn1xSb single crystals had 7 mm long regions pulled without and with ultrasound. These crystals were cut into 1.5–2 mm thick plates along the growth axis parallel to (2 1 1) plane to study the structure perfection and the growth striations in GaxIn1xSb single crystals. The cut surfaces were ground with 40 lm alumina abrasive and sufficiently polished with 5 lm Cr2O3. In order to reveal the growth striations under an optical microscope, samples of GaxIn1xSb single crystals were etched with mixed solution of 3HF, 3CH3COOH and 5HNO3 for 5–20 s at about 20 C. Besides, the samples were cut from regions grown without and with ultrasound, parallel to the pulling axis using electrical discharge machine (EDM) (Fig. 1a). These samples had rectangular parallelepiped shape to examine their electrophysical properties at 300 K. The size of these samples was up to 1.6 · 1.6 · 7 mm. The measurements of carrier concentration in GaxIn1xSb single crystals were carried out using Hall effect. 0.5 A electrical current was passed along the crystal length. Magnetic field induction was equal to 0.18 T. Four-point probe was used to perform the resistivity measurements. The two copper-constantan (Type T) thermocouples were used to measure the temperature. The occurring voltage in the crystal samples was
Fig. 1. GaxIn1xSb single crystal: (a) sketch of cut of GaxIn1xSb crystal for example the electrophysical properties and (b) growth striations.
821
measured using two cope probes. The temperature gradient in the samples was up to 1.8 K/cm. The sign of thermo emf in GaxIn1xSb single crystals was determined based on the known negative thermo emf in Bi single crystals. The random errors of measurements of carrier concentration, electrical resistivity and thermal emf did not exceed ±3%, ±2% and ±2%, respectively. The structure perfection was investigated by double crystal X-ray diffraction mode using CuKa1-radiation and Ge(1 1 1) monochromator. The (4 2 2) reflection and (n, m) scheme were used for the rocking curve measurements. The rocking curves obtained by the X-ray diffraction indicated the perfect structure of grown GaxIn1xSb single crystals. Disoriented blocks with grain-boundary angles less than 0.1 were observed, whereas the half-width was about 0.05. Ga-enriched striations with a period of 7–110 lm were located parallel to the crystallization front at the center as well as at the periphery of the crystals grown without ultrasonic field. The spacing between striations was increased with the decrease of crystal rotation rate. The striation width was about 1 lm. There were no striations with a period exceeding 14 lm in the crystal regions pulled under ultrasonic field (Fig. 1b). This was observed in the crystals with constant and variable diameter. However, we could not eliminate the striations with a period of 7–14 lm, which were observed in all crystal regions. The results of measurements of electrophysical properties in pulled GaxIn1xSb single crystals were presented in Table 1. Hall effect measurements indicated that all samples were of n-type conductivity. The resistivity has a tendency of reducing in the samples grown in the presence of ultrasonic waves. Simultaneously the carrier mobilities in samples of crystal pulled with ultrasonic field increase on 23–46%. The reduction of the resistivity and increase in the carrier mobility in the crystal samples grown under ultrasound can be explained by the increase in carrier diffusion due to more compositional homogeneity and less quantity of the structure defects. Additionally, the measured thermo emf in these crystal samples was larger on 22–32% than that in the crystal samples obtained without ultrasound. Based on the results of the investigation carried out in the GaxIn1xSb single crystals, it was concluded that the ultrasonic waves at frequencies of 0.72–1.44 MHz are a useful tool for improvement of the crystal quality. Carrier mobility and thermo emf can be increased due to the reduced striations in single crystals grown with ultrasound.
Table 1 Electrophysical properties of GaxIn1xSb single crystals Parameters
GaxIn1xSb single crystals grown without ultrasound 3
Electron concentration, nk (cm ) Electrical resistivity, qy (X cm) Carrier mobilities, ln (cm2/V s) Thermal emf, a1,2 (lV/K )
16
(2.53 ± 0.05) · 10 (49.6 ± 1) · 104 (5 ± 0.2) · 104 130 ± 3
GaxIn1xSb single crystals grown with ultrasound (2.57 ± 0.05) · 1016 (36.5 ± 0.7) · 104 (6.7 ± 0.3) · 104 165 ± 3
822
G.N. Kozhemyakin et al. / Solid-State Electronics 51 (2007) 820–822
Acknowledgement The authors thank Dr. A. Churilov for helpful discussions. References [1] Pino R, Ko Y, Dutta PS. Burstein–Moss shift in impurity-compensated bulk GaxIn1xSb substrates. J Appl Phys 2004;96:5349–52. [2] Collins S, Birdwell AG, Glosser R. Characterization of InGaSb by photoreflectance spectroscopy. J Appl Phys 2002;91:1175–8. [3] Dutta PS. III–V Ternary bulk substrate growth technology: a review. J Cryst Growth 2005;275:106–11. [4] Stelian C, Duffar T, Mitric A. Growth of concentrated GaInSb alloys with improved chemical homogeneity at low and variable pulling rates. J Cryst Growth 2005;283:124–33. [5] Dutta PS, Ostrogorsky AG. Suppression of cracks in InxGa1xSb crystals through forced convection in the melt. J Cryst Growth 1998;194:1–7. [6] Kinoshita K, Kato H, Matsumoto S. Growth of homogeneous InxGa1xSb crystals by the graded solute concentration method. J Cryst Growth 2000;216:37–43.
[7] Tanaka A, Shintani J, Kimura M. Multi-step pulling of GaInSb bulk crystal from ternary solution. J Cryst Growth 2000;209:625–9. [8] Kozhemyakin GN. Indium inhomogeneity in InxGa1xSb ternary crystals grown by floating crucible Czochralski method. J Cryst Growth 2000;220:39–45. [9] Tsaur SC, Kou S. Growth of Ga1xInxSb alloy crystals by conventional Czochralski pulling. J Cryst Growth 2003;249:470–6. [10] Kozhemyakin GN. Influence of ultrasonic vibrations on the growth of semiconductors single crystals. Ultrasonics 1998;35:599–604. [11] Kozhemyakin GN, Kolodyazhanaya LG. Growth striations in Bi–Sb alloy single crystals pulled in the presence of ultrasonic vibrations. J Cryst Growth 1995;147:200–6. [12] Kozhemyakin GN. Influence of ultrasonic vibrations on the growth of InSb crystals. J Cryst Growth 1995;149:266–8. [13] Tsuruta T, Hayakawa Y, Kumagawa M. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals. Jpn J Appl Phys 1988;27:47–9. [14] Tsuruta T, Hayakawa Y, Kumagawa M. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals (II). Jpn J Appl Phys 1989;28:36–8. [15] Tsuruta T, Yamashita K, Adachi S. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals (III). Jpn J Appl Phys 1992;31:23–5.
Letter
Influence of ultrasound on the growth striations and electrophysical properties of GaxIn1xSb single crystals G.N. Kozhemyakin a
a,*
, L.V. Zolkina a, M.A. Rom
b
Laboratory of Crystal Growth, The V. Dal Eastern Ukrainian National University, Bl. Molodezhniy, 20 A, Lugansk 91034, Ukraine b Institute for Single Crystals, National Academy of Science of Ukraine, 60 Lenin Street, Kharkiv 61001, Ukraine Received 5 September 2006; received in revised form 30 April 2007; accepted 9 May 2007
The review of this paper was arranged by Prof. Y. Arakawa
Abstract Effect of ultrasonic waves on growth striations and electrophysical properties of GaxIn1xSb single crystals with x up to 0.03 have been investigated. A decrease in the ultrasound field of growth striations in GaxIn1xSb single crystals has been observed. The carrier concentration and thermal emf in these crystals were larger than that in crystals pulled without ultrasound. 2007 Elsevier Ltd. All rights reserved. PACS: 150.100 Compound semiconductors Keywords: Solid solutions; Czochralski method; Growth from melt; GaInSb single crystal; Semiconducting ternary compounds
GaxIn1xSb single crystals with a band gap from 0.73 to 0.17 eV are of great interest for optoelectronic devices, because their wavelength can be varied in the range of 1.7–7 lm, depending on the composition [1,2]. However, such problems as polycrystalline growth, axial and radial compositional inhomogeneities etc., are inherent to growth of GaxIn1xSb crystals [3,4]. Therefore, a lot of work was dedicated to the growth process of GaxIn1xSb single crystals [5–9]. Recently, Tsaur et al. [9] grew GaxIn1xSb single crystals with InSb concentrations up to 23 mol% using the conventional Czochralski process. It was reported that pulled crystals had significant axial and radial segregation of InSb [8]. To reduce the components’ inhomogeneity in the single crystals, Czochralski method with ultrasound field can be employed [10]. The ultrasound at a frequency of about 1 MHz influenced the growth process positively by eliminating the striations in GaAs crystals, Bi–Sb single
*
Corresponding author. Tel.: +380 642 917 924; fax: +380 642 413 160. E-mail address: [email protected] (G.N. Kozhemyakin).
0038-1101/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.sse.2007.05.002
crystals with constant diameter and in the facet region of InSb single crystals [10–12]. Originally, growth of GaxIn1xSb crystals in ultrasound field was investigated by Hayakawa [13–15]. Experiments showed that the application of ultrasound at a frequency of 10 kHz and power up to 120 W did not provide high quality single crystals due to the melt cavitations and flow patterns with high speed [13–15]. This article describes the growth of GaxIn1xSb single crystals with x up to 0.03 under megahertz range ultrasound, investigation of the growth striations in the pulled single crystals and the results of the measurements of carrier concentration and mobility, electrical resistivity and thermal emf in pulled crystals. GaxIn1xSb single crystals were grown by a modified Czochralski method using InSb seed single crystals in the h1 1 1iB direction. The melt mass did not exceed 80 g. The pulling and rotation rates of the crystals were 3 mm/h and from 1 to 10 rpm, respectively. A fused silica crucible of 40 ID and 30 mm height was not rotated. Ga, In and Sb of 6 N were used as source materials. The crystals were
G.N. Kozhemyakin et al. / Solid-State Electronics 51 (2007) 820–822
pulled in high purity Ar. Ultrasound at frequencies of 0.72 and 1.44 MHz was introduced into the melt from a piezotransducer through a fused silica waveguide, with 10 mm diameter and 300 mm length, fused to the bottom of silica crucible. The direction of ultrasonic waves was parallel to the pulling axis. Grown GaxIn1xSb single crystals had 7 mm long regions pulled without and with ultrasound. These crystals were cut into 1.5–2 mm thick plates along the growth axis parallel to (2 1 1) plane to study the structure perfection and the growth striations in GaxIn1xSb single crystals. The cut surfaces were ground with 40 lm alumina abrasive and sufficiently polished with 5 lm Cr2O3. In order to reveal the growth striations under an optical microscope, samples of GaxIn1xSb single crystals were etched with mixed solution of 3HF, 3CH3COOH and 5HNO3 for 5–20 s at about 20 C. Besides, the samples were cut from regions grown without and with ultrasound, parallel to the pulling axis using electrical discharge machine (EDM) (Fig. 1a). These samples had rectangular parallelepiped shape to examine their electrophysical properties at 300 K. The size of these samples was up to 1.6 · 1.6 · 7 mm. The measurements of carrier concentration in GaxIn1xSb single crystals were carried out using Hall effect. 0.5 A electrical current was passed along the crystal length. Magnetic field induction was equal to 0.18 T. Four-point probe was used to perform the resistivity measurements. The two copper-constantan (Type T) thermocouples were used to measure the temperature. The occurring voltage in the crystal samples was
Fig. 1. GaxIn1xSb single crystal: (a) sketch of cut of GaxIn1xSb crystal for example the electrophysical properties and (b) growth striations.
821
measured using two cope probes. The temperature gradient in the samples was up to 1.8 K/cm. The sign of thermo emf in GaxIn1xSb single crystals was determined based on the known negative thermo emf in Bi single crystals. The random errors of measurements of carrier concentration, electrical resistivity and thermal emf did not exceed ±3%, ±2% and ±2%, respectively. The structure perfection was investigated by double crystal X-ray diffraction mode using CuKa1-radiation and Ge(1 1 1) monochromator. The (4 2 2) reflection and (n, m) scheme were used for the rocking curve measurements. The rocking curves obtained by the X-ray diffraction indicated the perfect structure of grown GaxIn1xSb single crystals. Disoriented blocks with grain-boundary angles less than 0.1 were observed, whereas the half-width was about 0.05. Ga-enriched striations with a period of 7–110 lm were located parallel to the crystallization front at the center as well as at the periphery of the crystals grown without ultrasonic field. The spacing between striations was increased with the decrease of crystal rotation rate. The striation width was about 1 lm. There were no striations with a period exceeding 14 lm in the crystal regions pulled under ultrasonic field (Fig. 1b). This was observed in the crystals with constant and variable diameter. However, we could not eliminate the striations with a period of 7–14 lm, which were observed in all crystal regions. The results of measurements of electrophysical properties in pulled GaxIn1xSb single crystals were presented in Table 1. Hall effect measurements indicated that all samples were of n-type conductivity. The resistivity has a tendency of reducing in the samples grown in the presence of ultrasonic waves. Simultaneously the carrier mobilities in samples of crystal pulled with ultrasonic field increase on 23–46%. The reduction of the resistivity and increase in the carrier mobility in the crystal samples grown under ultrasound can be explained by the increase in carrier diffusion due to more compositional homogeneity and less quantity of the structure defects. Additionally, the measured thermo emf in these crystal samples was larger on 22–32% than that in the crystal samples obtained without ultrasound. Based on the results of the investigation carried out in the GaxIn1xSb single crystals, it was concluded that the ultrasonic waves at frequencies of 0.72–1.44 MHz are a useful tool for improvement of the crystal quality. Carrier mobility and thermo emf can be increased due to the reduced striations in single crystals grown with ultrasound.
Table 1 Electrophysical properties of GaxIn1xSb single crystals Parameters
GaxIn1xSb single crystals grown without ultrasound 3
Electron concentration, nk (cm ) Electrical resistivity, qy (X cm) Carrier mobilities, ln (cm2/V s) Thermal emf, a1,2 (lV/K )
16
(2.53 ± 0.05) · 10 (49.6 ± 1) · 104 (5 ± 0.2) · 104 130 ± 3
GaxIn1xSb single crystals grown with ultrasound (2.57 ± 0.05) · 1016 (36.5 ± 0.7) · 104 (6.7 ± 0.3) · 104 165 ± 3
822
G.N. Kozhemyakin et al. / Solid-State Electronics 51 (2007) 820–822
Acknowledgement The authors thank Dr. A. Churilov for helpful discussions. References [1] Pino R, Ko Y, Dutta PS. Burstein–Moss shift in impurity-compensated bulk GaxIn1xSb substrates. J Appl Phys 2004;96:5349–52. [2] Collins S, Birdwell AG, Glosser R. Characterization of InGaSb by photoreflectance spectroscopy. J Appl Phys 2002;91:1175–8. [3] Dutta PS. III–V Ternary bulk substrate growth technology: a review. J Cryst Growth 2005;275:106–11. [4] Stelian C, Duffar T, Mitric A. Growth of concentrated GaInSb alloys with improved chemical homogeneity at low and variable pulling rates. J Cryst Growth 2005;283:124–33. [5] Dutta PS, Ostrogorsky AG. Suppression of cracks in InxGa1xSb crystals through forced convection in the melt. J Cryst Growth 1998;194:1–7. [6] Kinoshita K, Kato H, Matsumoto S. Growth of homogeneous InxGa1xSb crystals by the graded solute concentration method. J Cryst Growth 2000;216:37–43.
[7] Tanaka A, Shintani J, Kimura M. Multi-step pulling of GaInSb bulk crystal from ternary solution. J Cryst Growth 2000;209:625–9. [8] Kozhemyakin GN. Indium inhomogeneity in InxGa1xSb ternary crystals grown by floating crucible Czochralski method. J Cryst Growth 2000;220:39–45. [9] Tsaur SC, Kou S. Growth of Ga1xInxSb alloy crystals by conventional Czochralski pulling. J Cryst Growth 2003;249:470–6. [10] Kozhemyakin GN. Influence of ultrasonic vibrations on the growth of semiconductors single crystals. Ultrasonics 1998;35:599–604. [11] Kozhemyakin GN, Kolodyazhanaya LG. Growth striations in Bi–Sb alloy single crystals pulled in the presence of ultrasonic vibrations. J Cryst Growth 1995;147:200–6. [12] Kozhemyakin GN. Influence of ultrasonic vibrations on the growth of InSb crystals. J Cryst Growth 1995;149:266–8. [13] Tsuruta T, Hayakawa Y, Kumagawa M. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals. Jpn J Appl Phys 1988;27:47–9. [14] Tsuruta T, Hayakawa Y, Kumagawa M. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals (II). Jpn J Appl Phys 1989;28:36–8. [15] Tsuruta T, Yamashita K, Adachi S. Effect of ultrasonic vibrations on the growth of InxGa1xSb mixed crystals (III). Jpn J Appl Phys 1992;31:23–5.