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Equilibrium partial pressures and crystal growth of Cd1−xZnxTe
CRYS=407=C Mamatha=Venkatachala=BG
Journal of Crystal Growth 214/215 (2000) 30}34
Equilibrium partial pressures and crystal growth of Cd Zn Te \V V Wenbin Sang*, Yongbiao Qian, Weiming Shi, Linjun Wang, Ju Yang, Donghua Liu School of Materials Science and Engineering, Jiading Campus, Shanghai University, No. 20 Chengzhong Road, Jiading, Shanghai 201800, People's Republic of China
Abstract The partial pressures, p and p , over Cd Zn Te (CZT) and Cd Zn melts were estimated based on known ! 8 \V V \V V thermodynamic data and the partial pressures, p and p , over Cd Zn alloy melt at a temperature of about ! 8 9803C could be equilibrium with those over Cd Zn Te melt at a melting temperature of 11623C. The Cd Zn Te crystal growth from the melt under controlled constituent partial pressures, provided by Cd Zn alloy instead of only Cd source was carried out in this work. The best result for the resistivity, which has reached up to about 10 ) cm, has been obtained under the equilibrium partial pressures estimated by thermodynamic relationships. The axial variation in Zn concentration, which has been obviously improved due to the Zn replenishment from the reservoir during the whole growth procedure, is within about 4%. EPD on the average was about 2;10 and 4;10 cm\ at the middle of the bulk. IR transmissivity in the range of 2 to 42 lm is larger than 60%. In addition, the relationship between resistivities and conducting types of the crystal and di!erent controlled pressures is also discussed. 2000 Elsevier Science B.V. All rights reserved. Keywords: Equilibrium partial pressure; CdZnTe crystal growth; Gamma detector
1. Introduction There is a growing interest in the bulk growth of Cd Zn Te (CZT) crystals of high resistivity for \V V fabricating x, c-ray detectors. The CZT crystals of o&10 ) cm, suitable for x, c-ray detectors, have been successfully grown via the high pressure Bridgeman technique (HPB)[1}3]. Alternatively CZT crystals of high resistivity were grown by modi"ed vertical Bridgeman (MVB) technique un* Corresponding author. Tel.: #86-21-59525532; fax: #8621-59525532. E-mail address: [email protected] (W.B. Sang).
der controlled Cd pressure, but the resistivity obtained could only reach up to about 10 ) cm [4,5]. The di$culties involved might be caused by illde"ned thermodynamic conditions. However, at present the partial pressures of constituent elements, especially of Zn, over the melts are still de"cient in the literature and usually the controlled pressures used in the growth are empirically determined. In this paper, we will present our recent attempts to grow CZT crystals of high resistivity from the melts under controlled constituent partial pressures, provided by Cd Zn source instead of \V V only Cd source, based on the results obtained by thermodynamic evaluation.
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 0 4 8 - 8
Crys=407=CM=VVC=BG
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
31
2. Equilibrium partial pressures over CZT and Cd1+x Znx melts The equilibrium partial pressures, p and p , ! 8 over CZT crystals have ever been studied [6,7]. However, p and p over the CZT above its ! 8 melting point have not yet been reported in the literature. The equilibrium partial pressures over CZT and Cd Zn melts were estimated based on \V V known thermodynamic data [8}10], assuming that CZT or Cd Zn melt does not deviate from \V V a regular melt very much, which are shown in Figs. 1 and 2, respectively. It can been found from
Fig. 2. p}X relationship for Cd Zn melt at di!erent temper\V V atures. Intersecting points between curves representing p , p ! 8 over the Cd Zn melt and lines representing p (6.9;10 Pa) \V V ! and p (0.84;10 Pa) over Cd Zn Te melt at a temperature 8 of 11623C is located at x"0.14.
Fig. 1 that p and p over Cd Zn Te melt at ! 8 a temperature of 11623C are about 6.9;10 and 0.84;10 Pa, respectively. Fig. 2 shows that the intersecting points between the lines representing the p (6.9;10 Pa), p (0.84;10 Pa) and ! 8 the curves representing the p , p over the ! 8 Cd Zn melt are situated at an x value of 0.14 \V V and a temperature of 9803C. Thus, it can be considered that the partial pressures over Cd Zn Te melt at a temperature of 11623C would be in equilibrium with those over Cd Zn alloy source at a temperature of 9803C.
3. CdZnTe crystal growth
Fig. 1. Equilibrium partial pressure over CZT melt as a function of Zn mole fraction, x, in Cd Zn Te melt (a) p (b) p . \V V ! 8
The crystal growth apparatus consists of threestacked tubular electric furnaces. The upper furnace is used to control the temperature of alloy reservoir, or Cd reservoir. It has a heat pipe to maintain a #at temperature pro"le. The middle furnace is the hot zone, held above the melting point of the material. The lower furnace is the cold zone accommodating a heat pipe to passively maintain a #at temperature pro"le. The starting
Crys=407=CM=VVC=BG
32
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
materials were commercial Cd, Zn and Te elements of 6N purity, which were puri"ed to 7N in our laboratory. A mixture of polycrystalline ZnTe and CdTe synthesized from the puri"ed elements, respectively, was further puri"ed through vaporphase transport to reduce the content of poisonous impurities such as Cu, Fe and Ni. The puri"ed crystallites of CZT were then loaded into a quartz crucible, and alloy reservoir, or Cd reservoir, used for vapor control, was located at the upper part of the crucible with a separate temperature control. For compounding and growth runs, the crucibles were coated with pyrolytic carbon with acetone. The axial temperature gradient at the interface between solid and liquid phase was 15}203C/cm. The CZT MVB growth at a rate of 1}2 mm/h was carried out under controlled pressures by using Cd Zn alloy and occasionally Cd reservoir at a "xed temperature. After the growth was complete, the temperature of the reservoir was lowered at a proper rate with the hot crystal cooling down to room temperature at a rate of 53C/h.
Fig. 3. Zn axial composition pro"le of crystals grown in the presence of both Cd and Zn in the vapor (䉲), compared with that grown with only Cd (䊏).
4. Results and discussion The as-grown bulks were typically about 60}80 mm in length and about 20}30 mm in diameter, and usually contained three or four grains. However, almost single-grain wafers (20;40 mm) containing no twin have also been obtained. Cathodoluminesence (CL) microscopy showed that the structural perfect of the crystal grown under both p and p was rather good and was ! 8 better than that under only p . Conventional de! fect revealing etch method on wafers from di!erent position was also made. The Nakagawa etchant (3 ml HF#20 ml H O #20 ml H O) revealed that randomly distributed etch pit density (EPD) on the average was about 2;10 and 4;10 cm\ at the middle of the bulk. The axial variation in Zn concentration, caused by the signi"cantly larger than unit Zn distribution coe$cient (K (CdTe)"1.35) [11], in CZT crys8 tals grown by using the alloy reservoir is within about 4%, which has been obviously improved, compared with that in the crystals grown under only p (see Fig. 3). This might be due to the Zn !
Fig. 4. IR transmission of Cd Zn Te crystal grown using Cd Zn alloy source at 9803C
replenishment from the reservoir during the crystal growth process. However, the segregation still occurred even with the Zn replenishment. The reason for this might be due to the fact that the solute di!using transport was dominated in our case for relatively small diameter ampoule, where the convection was rather limited. Therefore, the replenishing Zn from the reservoir might not have enough time to be completely transported to the growth
Crys=407=CM=VVC=BG
1080 13.6 1.6 15.2 6.9;10 n 1040 10.3 1.1 11.4 2.6;10 n 985 7.1 0.9 8.0 8.5;10 Weak n 980 6.7 0.8 7.5 9.3;10 Weak P 980 6.7 0.8 7.5 1.1;10 * 975 6.5 0.7 7.2 8.2;10 Weak p 960 5.9 0.6 6.5 6.5;10 p 940 4.8 0.5 5.3 5.7;10 p 6.8 2.3;10 p 5.2 7.3;10 p
880 2.8 0.3 3.1 7.6;10 p 6.8 5.2
Temperature of Cd Zn (3C) Partial pressure of Cd (10 P a) Partial pressure of Zn (10 Pa) Total partial pressures P (10 Pa) Resistivity () cm) Electrical type
CZ-25 CZ-15 CZ-14 CZ-05 CZ-02 C-03 C-01 Serial of sample
Table 1 The electrical performances of crystals grown by MVB method under di!erent partial pressures of both Cd and Zn
CZ-18
CZ-19
CZ-08
CZ-11
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
33
interface. If the convection is reinforced, for instance, by rotating the ampoule, or the growth rate is optimized, the segregation might be avoided with the Zn replenishment. Further work is needed. Infrared transmission in the range of 2}42 lm for the crystal grown in the presence of optimum Cd and Zn in the vapor is larger than 60% (see Fig. 4). Electrical properties were determined using ZC36 micro-current instrument. Ohmic contacts were made using AuCl chemical deposition for p-type crystal and indium solder under a nitrogen #ux for n-type. The resistivities and electric conducting types of the crystals under di!erent Cd and Zn pressure are listed in Table 1. It indicates that the resistivities and conduction types of the crystals are closely related to the controlled partial pressures. Assuming the crystal is free of impurities, the resistivities and conduction types would be dominated by the concentration of intrinsic defects like Cd, Zn vacancy or Cd interstitial in crystal, which are controlled by surrounding vapor pressures. Thus, the as-grown crystal obtained in the vapor of rather low or over high pressures has lower resistivity and appears to be p- or n-type, respectively. In the region approaching to equilibrium partial pressures, under which the grown crystal would be of higher resistivity and intrinsic or of weak p- or n-type. The resistivity of Cd Zn Te crystals grown under precisely controlled partial pressures, provided by Cd Zn source at 9803C, reached up to about 10 ) cm, which was of 1}2 order higher than that obtained only under controlled Cd partial pressure reported in the literature [5]. The di!erence might be attributed to the controlled pressures, especially, the role of Zn in the vapor during cooling-down to room temperature throughout the post growth. In addition, this result, in turn, indicates that the equilibrium partial pressures obtained by thermodynamic evaluation are of theoretical and practical interest.
5. Conclusions The equilibrium partial pressures over CZT and Cd Zn melts have been determined based on \V V thermodynamic evaluation. The results indicate that p and p over Cd Zn Te melt at a ! 8
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W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
temperature of 11623C are about 6.9;10 and 0.84;10 Pa, respectively, in equilibrium with those over Cd Zn alloy sources at a temper ature of 9803C. The resistivity of Cd Zn Te crystal grown under both p and p in the vapor, provided by ! 8 Cd Zn source at 9803C, reached up to about 10 ) cm, which was of 1}2 order higher than that reported in the literature using the same method. This result, in turn, indicates that the equilibrium partial pressures obtained by thermodynamic evaluation are of theoretical and practical interest. In addition, the structure perfection, Zn axial distribution, and IR transmission of the crystals have also been improved. This might be attributed to the fact that p would not be negligible in 8 comparison with that of Cd, and that the melts (or as-grown crystals) at higher temperatures could decompose without the presence of Zn in vapor, in addition to Cd.
Acknowledgements The authors are grateful to the National Natural Science Funds of China for providing "nancial
support for this work under Grant No. 19675025 and the support of K.C. Wong Education Foundation, Hong Kong.
References [1] Y. Eisen, A. Shor, J. Crystal Growth 184 (1998) 1310. [2] J.F. Butler, C.L. Lingren, F.P. Doty, IEEE Trans. Nucl. Sci. 39 (1992) 605. [3] A. Niemela, H. Sipila, IEEE Trans. Nucl. Sci. 41 (1994) 1054. [4] H.L. Glass, A.J. Socha, C.L. Parfeniuk, J. Crystal Growth 184/185 (1998) 1035. [5] K. Peters et al., Crystal Res. Technol. 25 (1990) 1107. [6] H.R. Vydyannath, J.A. Ellsworth, J. Electron. Mater. 22 (8) (1993) 1067. [7] R.F. Brebrick, T.C. Yu, Metallurg. Mater. Trans. A 26 A (10) (1995) 2597. [8] Tse Tung, Ching-Hua Su, Pok-Kai Liao, J. Vac. Technol. 21 (1) (1982) 117. [9] A.S. Jordan, Metallurgical Trans. 1 (1970) 239. [10] R. Hultgren, R.L. Orr, P.D. Anderson, K.K. Kelley, Selected Values of Thermodynamic Properties of Metals and Alloys, Wiley, 1963, p. 637. [11] A. Tanaka, Y. Masa, S. Seto, T. Kawasaki, J. Crystal Growth 94 (1989) 166.
Journal of Crystal Growth 214/215 (2000) 30}34
Equilibrium partial pressures and crystal growth of Cd Zn Te \V V Wenbin Sang*, Yongbiao Qian, Weiming Shi, Linjun Wang, Ju Yang, Donghua Liu School of Materials Science and Engineering, Jiading Campus, Shanghai University, No. 20 Chengzhong Road, Jiading, Shanghai 201800, People's Republic of China
Abstract The partial pressures, p and p , over Cd Zn Te (CZT) and Cd Zn melts were estimated based on known ! 8 \V V \V V thermodynamic data and the partial pressures, p and p , over Cd Zn alloy melt at a temperature of about ! 8 9803C could be equilibrium with those over Cd Zn Te melt at a melting temperature of 11623C. The Cd Zn Te crystal growth from the melt under controlled constituent partial pressures, provided by Cd Zn alloy instead of only Cd source was carried out in this work. The best result for the resistivity, which has reached up to about 10 ) cm, has been obtained under the equilibrium partial pressures estimated by thermodynamic relationships. The axial variation in Zn concentration, which has been obviously improved due to the Zn replenishment from the reservoir during the whole growth procedure, is within about 4%. EPD on the average was about 2;10 and 4;10 cm\ at the middle of the bulk. IR transmissivity in the range of 2 to 42 lm is larger than 60%. In addition, the relationship between resistivities and conducting types of the crystal and di!erent controlled pressures is also discussed. 2000 Elsevier Science B.V. All rights reserved. Keywords: Equilibrium partial pressure; CdZnTe crystal growth; Gamma detector
1. Introduction There is a growing interest in the bulk growth of Cd Zn Te (CZT) crystals of high resistivity for \V V fabricating x, c-ray detectors. The CZT crystals of o&10 ) cm, suitable for x, c-ray detectors, have been successfully grown via the high pressure Bridgeman technique (HPB)[1}3]. Alternatively CZT crystals of high resistivity were grown by modi"ed vertical Bridgeman (MVB) technique un* Corresponding author. Tel.: #86-21-59525532; fax: #8621-59525532. E-mail address: [email protected] (W.B. Sang).
der controlled Cd pressure, but the resistivity obtained could only reach up to about 10 ) cm [4,5]. The di$culties involved might be caused by illde"ned thermodynamic conditions. However, at present the partial pressures of constituent elements, especially of Zn, over the melts are still de"cient in the literature and usually the controlled pressures used in the growth are empirically determined. In this paper, we will present our recent attempts to grow CZT crystals of high resistivity from the melts under controlled constituent partial pressures, provided by Cd Zn source instead of \V V only Cd source, based on the results obtained by thermodynamic evaluation.
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 0 4 8 - 8
Crys=407=CM=VVC=BG
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
31
2. Equilibrium partial pressures over CZT and Cd1+x Znx melts The equilibrium partial pressures, p and p , ! 8 over CZT crystals have ever been studied [6,7]. However, p and p over the CZT above its ! 8 melting point have not yet been reported in the literature. The equilibrium partial pressures over CZT and Cd Zn melts were estimated based on \V V known thermodynamic data [8}10], assuming that CZT or Cd Zn melt does not deviate from \V V a regular melt very much, which are shown in Figs. 1 and 2, respectively. It can been found from
Fig. 2. p}X relationship for Cd Zn melt at di!erent temper\V V atures. Intersecting points between curves representing p , p ! 8 over the Cd Zn melt and lines representing p (6.9;10 Pa) \V V ! and p (0.84;10 Pa) over Cd Zn Te melt at a temperature 8 of 11623C is located at x"0.14.
Fig. 1 that p and p over Cd Zn Te melt at ! 8 a temperature of 11623C are about 6.9;10 and 0.84;10 Pa, respectively. Fig. 2 shows that the intersecting points between the lines representing the p (6.9;10 Pa), p (0.84;10 Pa) and ! 8 the curves representing the p , p over the ! 8 Cd Zn melt are situated at an x value of 0.14 \V V and a temperature of 9803C. Thus, it can be considered that the partial pressures over Cd Zn Te melt at a temperature of 11623C would be in equilibrium with those over Cd Zn alloy source at a temperature of 9803C.
3. CdZnTe crystal growth
Fig. 1. Equilibrium partial pressure over CZT melt as a function of Zn mole fraction, x, in Cd Zn Te melt (a) p (b) p . \V V ! 8
The crystal growth apparatus consists of threestacked tubular electric furnaces. The upper furnace is used to control the temperature of alloy reservoir, or Cd reservoir. It has a heat pipe to maintain a #at temperature pro"le. The middle furnace is the hot zone, held above the melting point of the material. The lower furnace is the cold zone accommodating a heat pipe to passively maintain a #at temperature pro"le. The starting
Crys=407=CM=VVC=BG
32
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
materials were commercial Cd, Zn and Te elements of 6N purity, which were puri"ed to 7N in our laboratory. A mixture of polycrystalline ZnTe and CdTe synthesized from the puri"ed elements, respectively, was further puri"ed through vaporphase transport to reduce the content of poisonous impurities such as Cu, Fe and Ni. The puri"ed crystallites of CZT were then loaded into a quartz crucible, and alloy reservoir, or Cd reservoir, used for vapor control, was located at the upper part of the crucible with a separate temperature control. For compounding and growth runs, the crucibles were coated with pyrolytic carbon with acetone. The axial temperature gradient at the interface between solid and liquid phase was 15}203C/cm. The CZT MVB growth at a rate of 1}2 mm/h was carried out under controlled pressures by using Cd Zn alloy and occasionally Cd reservoir at a "xed temperature. After the growth was complete, the temperature of the reservoir was lowered at a proper rate with the hot crystal cooling down to room temperature at a rate of 53C/h.
Fig. 3. Zn axial composition pro"le of crystals grown in the presence of both Cd and Zn in the vapor (䉲), compared with that grown with only Cd (䊏).
4. Results and discussion The as-grown bulks were typically about 60}80 mm in length and about 20}30 mm in diameter, and usually contained three or four grains. However, almost single-grain wafers (20;40 mm) containing no twin have also been obtained. Cathodoluminesence (CL) microscopy showed that the structural perfect of the crystal grown under both p and p was rather good and was ! 8 better than that under only p . Conventional de! fect revealing etch method on wafers from di!erent position was also made. The Nakagawa etchant (3 ml HF#20 ml H O #20 ml H O) revealed that randomly distributed etch pit density (EPD) on the average was about 2;10 and 4;10 cm\ at the middle of the bulk. The axial variation in Zn concentration, caused by the signi"cantly larger than unit Zn distribution coe$cient (K (CdTe)"1.35) [11], in CZT crys8 tals grown by using the alloy reservoir is within about 4%, which has been obviously improved, compared with that in the crystals grown under only p (see Fig. 3). This might be due to the Zn !
Fig. 4. IR transmission of Cd Zn Te crystal grown using Cd Zn alloy source at 9803C
replenishment from the reservoir during the crystal growth process. However, the segregation still occurred even with the Zn replenishment. The reason for this might be due to the fact that the solute di!using transport was dominated in our case for relatively small diameter ampoule, where the convection was rather limited. Therefore, the replenishing Zn from the reservoir might not have enough time to be completely transported to the growth
Crys=407=CM=VVC=BG
1080 13.6 1.6 15.2 6.9;10 n 1040 10.3 1.1 11.4 2.6;10 n 985 7.1 0.9 8.0 8.5;10 Weak n 980 6.7 0.8 7.5 9.3;10 Weak P 980 6.7 0.8 7.5 1.1;10 * 975 6.5 0.7 7.2 8.2;10 Weak p 960 5.9 0.6 6.5 6.5;10 p 940 4.8 0.5 5.3 5.7;10 p 6.8 2.3;10 p 5.2 7.3;10 p
880 2.8 0.3 3.1 7.6;10 p 6.8 5.2
Temperature of Cd Zn (3C) Partial pressure of Cd (10 P a) Partial pressure of Zn (10 Pa) Total partial pressures P (10 Pa) Resistivity () cm) Electrical type
CZ-25 CZ-15 CZ-14 CZ-05 CZ-02 C-03 C-01 Serial of sample
Table 1 The electrical performances of crystals grown by MVB method under di!erent partial pressures of both Cd and Zn
CZ-18
CZ-19
CZ-08
CZ-11
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
33
interface. If the convection is reinforced, for instance, by rotating the ampoule, or the growth rate is optimized, the segregation might be avoided with the Zn replenishment. Further work is needed. Infrared transmission in the range of 2}42 lm for the crystal grown in the presence of optimum Cd and Zn in the vapor is larger than 60% (see Fig. 4). Electrical properties were determined using ZC36 micro-current instrument. Ohmic contacts were made using AuCl chemical deposition for p-type crystal and indium solder under a nitrogen #ux for n-type. The resistivities and electric conducting types of the crystals under di!erent Cd and Zn pressure are listed in Table 1. It indicates that the resistivities and conduction types of the crystals are closely related to the controlled partial pressures. Assuming the crystal is free of impurities, the resistivities and conduction types would be dominated by the concentration of intrinsic defects like Cd, Zn vacancy or Cd interstitial in crystal, which are controlled by surrounding vapor pressures. Thus, the as-grown crystal obtained in the vapor of rather low or over high pressures has lower resistivity and appears to be p- or n-type, respectively. In the region approaching to equilibrium partial pressures, under which the grown crystal would be of higher resistivity and intrinsic or of weak p- or n-type. The resistivity of Cd Zn Te crystals grown under precisely controlled partial pressures, provided by Cd Zn source at 9803C, reached up to about 10 ) cm, which was of 1}2 order higher than that obtained only under controlled Cd partial pressure reported in the literature [5]. The di!erence might be attributed to the controlled pressures, especially, the role of Zn in the vapor during cooling-down to room temperature throughout the post growth. In addition, this result, in turn, indicates that the equilibrium partial pressures obtained by thermodynamic evaluation are of theoretical and practical interest.
5. Conclusions The equilibrium partial pressures over CZT and Cd Zn melts have been determined based on \V V thermodynamic evaluation. The results indicate that p and p over Cd Zn Te melt at a ! 8
Crys=407=CM=VVC=BG
34
W.B. Sang et al. / Journal of Crystal Growth 214/215 (2000) 30}34
temperature of 11623C are about 6.9;10 and 0.84;10 Pa, respectively, in equilibrium with those over Cd Zn alloy sources at a temper ature of 9803C. The resistivity of Cd Zn Te crystal grown under both p and p in the vapor, provided by ! 8 Cd Zn source at 9803C, reached up to about 10 ) cm, which was of 1}2 order higher than that reported in the literature using the same method. This result, in turn, indicates that the equilibrium partial pressures obtained by thermodynamic evaluation are of theoretical and practical interest. In addition, the structure perfection, Zn axial distribution, and IR transmission of the crystals have also been improved. This might be attributed to the fact that p would not be negligible in 8 comparison with that of Cd, and that the melts (or as-grown crystals) at higher temperatures could decompose without the presence of Zn in vapor, in addition to Cd.
Acknowledgements The authors are grateful to the National Natural Science Funds of China for providing "nancial
support for this work under Grant No. 19675025 and the support of K.C. Wong Education Foundation, Hong Kong.
References [1] Y. Eisen, A. Shor, J. Crystal Growth 184 (1998) 1310. [2] J.F. Butler, C.L. Lingren, F.P. Doty, IEEE Trans. Nucl. Sci. 39 (1992) 605. [3] A. Niemela, H. Sipila, IEEE Trans. Nucl. Sci. 41 (1994) 1054. [4] H.L. Glass, A.J. Socha, C.L. Parfeniuk, J. Crystal Growth 184/185 (1998) 1035. [5] K. Peters et al., Crystal Res. Technol. 25 (1990) 1107. [6] H.R. Vydyannath, J.A. Ellsworth, J. Electron. Mater. 22 (8) (1993) 1067. [7] R.F. Brebrick, T.C. Yu, Metallurg. Mater. Trans. A 26 A (10) (1995) 2597. [8] Tse Tung, Ching-Hua Su, Pok-Kai Liao, J. Vac. Technol. 21 (1) (1982) 117. [9] A.S. Jordan, Metallurgical Trans. 1 (1970) 239. [10] R. Hultgren, R.L. Orr, P.D. Anderson, K.K. Kelley, Selected Values of Thermodynamic Properties of Metals and Alloys, Wiley, 1963, p. 637. [11] A. Tanaka, Y. Masa, S. Seto, T. Kawasaki, J. Crystal Growth 94 (1989) 166.