- Email: [email protected]
Effect of temperature on conversion of basal plane dislocations to treading edge dislocations during 4H-SiC homoepitaxiy
Journal of Crystal Growth 531 (2020) 125360
Contents lists available at ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Effect of temperature on conversion of basal plane dislocations to treading edge dislocations during 4H-SiC homoepitaxiy
T
⁎
L. Yang , L.X. Zhao, H.W. Wu Hebei Key Laboratory of New Semiconductor Materials, No. 21 Changsheng Street, Luquan Economic Dev. Zone, Hebei P.R 050200, China Hebei Poshing Electronics Technology Co. Ltd., No. 21 Changsheng Street, Luquan Economic Dev. Zone, Hebei P.R 050200, China
A R T I C LE I N FO
A B S T R A C T
Communicated by Chennai Guest Editor
4H-SiC homoepitaxial layer grown on 4° off-axis substrates is performed at various growth temperature by using the traditional chemical vapor deposition. The effect of growth temperature on propagation of basal plane dislocations from substrate to epitaxy was studied using the deep KOH etching and Synchrotron reflection X-ray topography, and the conversion mechanism was also investigated. It is found that the majority basal plane dislocations are converted to threading edge dislocations during epitaxial growth. Meanwhile, the two types of threading edge dislocations in epitaxial layer are observed after KOH etch. By the optimization of growth temperature, high quality epitaxial wafer with extremely low basal plane dislocations density (< 0.01 cm−2) can be obtained. The conversion rate is decreased during epitaxial growth with the increasing of growth temperature. It is suggested that the effective C/Si ratio on the growth interface is decreased at high temperature, leading to the suppression of lateral growth during epitaxial process.
Keywords: B2. 4H-SiC A1. Homepitaxial layer A1. Threading edge dislocations A1. Basal plane dislocations A3. Chemical vapor deposition
1. Introduction Silicon carbide power devices outperform conventional silicon devices in terms of current conduction switching are expected due to its unique properties, such as high electric breakdown field, high thermal conductivity, and high carrier saturation velocity and so on [1]. However, the further commercialization of SiC productions is hindered because of high defects density that the defects are originated from the substrates and epitaxial growth process [2]. So, it is more challenging to lower and eliminate crystalline defects in commercial SiC-based material. Nowadays, the dislocation density of commercial 4H-SiC wafer is very high such as threading screw dislocations (TSDs) for 300–500 cm−2, basal plane dislocations (BPDs) for 500–1000 cm−2 and threading edge dislocations (TEDs) for 2000–5000 cm−2 [3], and these dislocations can be propagated into the epitaxial layer during epitaxial growth. It is generally that almost all the TSDs and TEDs in the substrate are replicated in an epitaxial layer, and it is hard to eliminate of them using the epitaxial method. However, the most (> 90%) BPDs in the substrate are converted to TEDs within a few micrometers of an initial epitaxial layer without any special treatment and the rest is propagated in a SiC epitaxial layer along the basal plane during epitaxial growth. Meanwhile, the remaining BPDs in the epitaxial layer are considered as the source of stacking faults that lead to the performance degradation of bipolar devices with forward voltage drift and reverse ⁎
leakage current [4,5]. Therefore, the decreasing of BPDs in epitaxial layer is a very key issue. Many approaches have been reported to enhance the conversion of BPDs to TEDs, such as in and ex-situ etching prior to epitaxial growth, interruption during growth, C/Si ratio and so on [6–8]. In this paper, the 4H-SiC epitaxial layer grown on 4° off angle substrate is conducted by the method of chemical vapor deposition. Meanwhile, the conversion mechanism BPDs to TEDs is studied during epitaxial growth. In order to further understand the conversion mechanism, the morphology of BPDs in the substrate and epitaxial layer are investigated using deep KOH etching and X-ray topography observations. Furthermore, the influence of growth temperature on the conversion of BPDs to TEDs is also discussed. 2. Experimental The epitaxial growth was conducted in a commercial multi-wafer horizontal warm-wall planetary reactor with H2-TCS-C3H8 system [9]. And the 6 μm thick epitaxial layers were grown on 6 in., Si-face, n-type 4H-SiC substrates with off-axis of 4° towards [11–20] direction. Trichlorosilane (TCS) and propane (C3H8) were used as silicon source and carbon source, respectively. The carrier gas was hydrogen (H2) and the n-type doping gas was nitrogen (N2). The growth temperature was varied from 1550 ℃ to 1650 ℃. The different samples were grown on
Corresponding author. E-mail address: [email protected] (L. Yang).
https://doi.org/10.1016/j.jcrysgro.2019.125360 Received 31 August 2019; Received in revised form 12 November 2019; Accepted 15 November 2019 Available online 17 November 2019 0022-0248/ © 2019 Published by Elsevier B.V.
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
Fig. 1. Morphology of BPD etch pits in the substrate using the molten KOH at 500 for 30 min (a) and mechanism schematic of BPD converted TED in epitaxial growth (b).
growth, and the red circle marks are defined as the converted TEDs. It is found that converted BPDs present as a dislocation line ending at a write point, and propagate into epitaxial layer without write point in the topographic image. Meanwhile, the length of dislocation line for converted TEDs indicates the conversion of BPDs occurred in different thickness of an epitaxial layer. Fig. 3 shows the microscopy image of epitaxial wafer for 6 μm grown on 4° off-axis 4H-SiC substrate after molten KOH etching at 500 ℃ for 25 min (a) and 50 min (b). In the Fig. 3(a), the BPDs are not found. It is believed that the majority BPDs in the substrate are converted to relatively benign treading edge dislocations. Meanwhile, the origin of TEDs with in-grown or converted BPDs cannot be clearly distinguished in the epitaxial layer using the molten at 500 ℃ for 25 min. Subsequently, the same epitaxial layer is etched to 50 min and the microscopy image is shown in Fig. 3(b). With the increasing of etching time, the etching pits of surface in epitaxial layer become large compared to the Fig. 3(a). But their outlines are rounded hexagonal shape regardless of etching time. However, the etch pits of TEDs with different bottom morphology can be observed in the epitaxial layer, including the rounded hexagonal shape and shell shape. It is believed that the shell shape of TEDs bottom result from the conversion of BPDs in the substrate. Therefore, it is expected that the origin of TEDs in the epitaxial layer can be confirmed by deep KOH etching. To investigate the effect of growth temperature on the conversion of BPDs to TEDs during epitaxial growth, the various growth temperatures were executed at 20 ℃ lower than reference, reference and 40 ℃ higher than reference, respectively. As shown in the Fig. 4(a)–(c), the mapping distribution of BPDs in the epitaxial layers grown on different temperature is measured by using the optical surface analyzer with photoluminescence. The number of BPDs in epitaxial layer grown on high temperature is drastically increased. The BPD density of epitaxial layer is calculated and shown in Fig. 4(d). It is found that the almost free BPDs in epitaxial layer (＜0.01 cm−2) are obtained at the reference
the 4H-SiC substrate from the same ingot. The Synchrotron Monochromatic Beam X-ray Topography (SMBXT) studies were characterized to analyze the conversion of BPDs to TEDs during epitaxial growth. The BPDs density in epitaxial layer were measured using the optical surface analyzer (Lasertech: SICA 88). Meanwhile, in order to confirmed the correlation of same defect under different inspection, the samples were further etched by using the molten KOH at 500 ℃ and microscopy observation.
3. Results and discussion Fig. 1(a) shows the microscopy image of typical etch pit for dislocations on the 4° SiC substrate by using the molten KOH at 500 ℃ for 30 min. From the Fig. 1(a), it can be seen that the TEDs are hexagonal shape and the BPDs are shell shape with different directions, and the TSDs are not found in the area. The enlargement (inset) corresponding yellow dot line area shows that the feature of BPD is composed of two partials dislocations enclosing a stacking fault between them. It is well known that the step flow growth in down step direction and lateral growth perpendicular to the step flow direction can be simultaneously taken place during epitaxial growth [3,10]. In case of the step flow growth domination, the BPDs in substrate propagate into the epitaxial layer. On the contrary, the two sides of BPDs etch pits will come closer and merge, and the BPDs is converted to TEDs in the epitaxial growth. The mechanism schematic of BPDs converted TEDs is shown in the Fig. 1(b) during epitaxial growth. In order to investigate the conversion of BPDs in the substrate to TEDs during epitaxial growth, the dislocations of substrate and epitaxial layer (6 μm) for 4H-SiC are characterized by using the 〈11–28〉 reflection in grazing-incidence geometry, as shown in Fig. 2. Large or small bright spots and the dark line can be observed in the Fig. 2(a) and identified as TSDs, TEDs and BPDs, respectively [11]. Fig. 2(b) exhibits the morphology of BPDs taken from the same position after epitaxial
Fig. 2. SMBXT topography of BPDs in the 4H-SiC wafer. (a) substrate; (b) epitaxial wafer for 6 μm. 2
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
Fig. 3. Microscope images of an epi-layer grown on 4° off-axis 4H-SiC substrate after KOH etch at 500 ℃ for different time. (a) 25 min; (b) 50 min.
4. Conclusion
temperature. In addition, the lower BPD density can be also observed on the 20 ℃ lower than reference, but the large number of surface defects such as triangles, pits are found in the surface of epitaxial layer. It is believed that the effective C/Si ratio in the growth interface decrease significantly when the growth temperature is gradually increased at fixed C/Si ratio [12]. The growth mode of epitaxial growth depends strongly on the C/Si ratio. In the case of high C/Si ratio, the step flow growth is suppressed and the lateral growth is enhanced, leading to the high conversion rate of BPDs to TEDs. On the contrary, the conversion rate is decreased. However, a higher C/Si ratio can also induce a higher surface defect density because of 2D nucleation. Therefore, the high quality, low BPD epitaxial wafer can be obtained in a range of temperature
4H-SiC homoepitaxial layer is grown on 4° off-axis substrate by the traditional chemical vapor deposition. The growth temperature dependence of BPDs density in epitaxial layer is also investigated using the molten KOH etching and Synchrotron reflection X-ray topography observation. It is found that the majority BPDs are converted to TEDs in epitaxial process, and the origin of TEDs in epitaxial layer can be distinguished by the morphology difference of etch pits after deep KOH etching. The epitaxial layer with BPD density is successfully obtained as low as 0.01/cm−2 under lower temperature. It is well known that the lateral growth and step flow growth can be simultaneously taken place during epitaxial growth. If the lateral growth dominates, it is beneficial to enhance the conversion of BPDs to TEDs. As a result, the conversion
Fig. 4. BPDs distribution in epitaxial layer under various growth temperature. (a)-(c) mapping distribution and (d) density of BPDs in epitaxial layer with different growth temperature, respectively. 3
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
References
rate is decreased with the increasing of growth temperature. It is suggested that the effective C/Si ratio on the growth interface is decreased at high temperature, leading to the suppression of lateral growth during epitaxial process.
[1] [2] [3] [4] [5]
CRediT authorship contribution statement
[6]
L. Yang: Writing - original draft, Investigation, Visualization. L.X. Zhao: Conceptualization, Methodology, Formal analysis, Writing - review & editing. H.W. Wu: Data curation, Investigation.
[7] [8] [9] [10] [11]
Declaration of Competing Interest The authors declared that there is no conflict of interest.
[12]
4
F. La Via, M. Camarda, A. La Magna, Appl. Phys. Rev. 1 (3) (2014) 031301. Z. Zhang, T.S. Sudarshan, Appl. Phys. Letts. 87 (2005) 161917. H. Song, T. Sudarshan, J. Cryst. Growth 371 (2013) 94–101. R.E. Stahlbush, N.A. Mahadik, M.J. O'Loughlin, Mater. Sci. Forum 778–780 (2014) 309–312. R. Myers-Ward, B. VanMil, R. Stahlbush, S. Katz, J. McCrate, S. Kitt, C. Eddy, D. Gaskill, Mater. Sci. Forum 615–617 (2009) 105–108. T. Ohno, H. Yamaguchi, S. Kuroda, K. Kojima, T. Suzuki, K. Arai, J. Cryst. Growth 271 (2004) 1–7. H. Song, T. Rana, T. Sudarshan, J. Cryst. Growth 320 (2011) 95–102. B.L. VanMil, R.E. Stahlbush, R.L. Myers-Ward, K.-K. Lew, C.R. Eddy Jr., D.K. Gaskill, J. Vac. Sci. Technol., B 26 (2008) 1504–1507. L. Zhao, H. Wu, J. Cryst. Growth 507 (2019) 109–112. Z. Zhang, E. Moulton, T. Sudarshan, Appl. Phys. Lett. 89 (2006) 081910–81911. H. Wang, F. Wu, M. Dudley, B. Raghothamachar, G. Chung, J. Zhang, B. Thomas, E.K. Sanchez, S.G. Mueller, D. Hansen, M.J. Loboda, Mater. Sci. Forum 778–780 (2014) 328–331. S. Nishizawa, M. Pons, Chem. Vap. Deposition 12 (2006) 516–522.
Contents lists available at ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Effect of temperature on conversion of basal plane dislocations to treading edge dislocations during 4H-SiC homoepitaxiy
T
⁎
L. Yang , L.X. Zhao, H.W. Wu Hebei Key Laboratory of New Semiconductor Materials, No. 21 Changsheng Street, Luquan Economic Dev. Zone, Hebei P.R 050200, China Hebei Poshing Electronics Technology Co. Ltd., No. 21 Changsheng Street, Luquan Economic Dev. Zone, Hebei P.R 050200, China
A R T I C LE I N FO
A B S T R A C T
Communicated by Chennai Guest Editor
4H-SiC homoepitaxial layer grown on 4° off-axis substrates is performed at various growth temperature by using the traditional chemical vapor deposition. The effect of growth temperature on propagation of basal plane dislocations from substrate to epitaxy was studied using the deep KOH etching and Synchrotron reflection X-ray topography, and the conversion mechanism was also investigated. It is found that the majority basal plane dislocations are converted to threading edge dislocations during epitaxial growth. Meanwhile, the two types of threading edge dislocations in epitaxial layer are observed after KOH etch. By the optimization of growth temperature, high quality epitaxial wafer with extremely low basal plane dislocations density (< 0.01 cm−2) can be obtained. The conversion rate is decreased during epitaxial growth with the increasing of growth temperature. It is suggested that the effective C/Si ratio on the growth interface is decreased at high temperature, leading to the suppression of lateral growth during epitaxial process.
Keywords: B2. 4H-SiC A1. Homepitaxial layer A1. Threading edge dislocations A1. Basal plane dislocations A3. Chemical vapor deposition
1. Introduction Silicon carbide power devices outperform conventional silicon devices in terms of current conduction switching are expected due to its unique properties, such as high electric breakdown field, high thermal conductivity, and high carrier saturation velocity and so on [1]. However, the further commercialization of SiC productions is hindered because of high defects density that the defects are originated from the substrates and epitaxial growth process [2]. So, it is more challenging to lower and eliminate crystalline defects in commercial SiC-based material. Nowadays, the dislocation density of commercial 4H-SiC wafer is very high such as threading screw dislocations (TSDs) for 300–500 cm−2, basal plane dislocations (BPDs) for 500–1000 cm−2 and threading edge dislocations (TEDs) for 2000–5000 cm−2 [3], and these dislocations can be propagated into the epitaxial layer during epitaxial growth. It is generally that almost all the TSDs and TEDs in the substrate are replicated in an epitaxial layer, and it is hard to eliminate of them using the epitaxial method. However, the most (> 90%) BPDs in the substrate are converted to TEDs within a few micrometers of an initial epitaxial layer without any special treatment and the rest is propagated in a SiC epitaxial layer along the basal plane during epitaxial growth. Meanwhile, the remaining BPDs in the epitaxial layer are considered as the source of stacking faults that lead to the performance degradation of bipolar devices with forward voltage drift and reverse ⁎
leakage current [4,5]. Therefore, the decreasing of BPDs in epitaxial layer is a very key issue. Many approaches have been reported to enhance the conversion of BPDs to TEDs, such as in and ex-situ etching prior to epitaxial growth, interruption during growth, C/Si ratio and so on [6–8]. In this paper, the 4H-SiC epitaxial layer grown on 4° off angle substrate is conducted by the method of chemical vapor deposition. Meanwhile, the conversion mechanism BPDs to TEDs is studied during epitaxial growth. In order to further understand the conversion mechanism, the morphology of BPDs in the substrate and epitaxial layer are investigated using deep KOH etching and X-ray topography observations. Furthermore, the influence of growth temperature on the conversion of BPDs to TEDs is also discussed. 2. Experimental The epitaxial growth was conducted in a commercial multi-wafer horizontal warm-wall planetary reactor with H2-TCS-C3H8 system [9]. And the 6 μm thick epitaxial layers were grown on 6 in., Si-face, n-type 4H-SiC substrates with off-axis of 4° towards [11–20] direction. Trichlorosilane (TCS) and propane (C3H8) were used as silicon source and carbon source, respectively. The carrier gas was hydrogen (H2) and the n-type doping gas was nitrogen (N2). The growth temperature was varied from 1550 ℃ to 1650 ℃. The different samples were grown on
Corresponding author. E-mail address: [email protected] (L. Yang).
https://doi.org/10.1016/j.jcrysgro.2019.125360 Received 31 August 2019; Received in revised form 12 November 2019; Accepted 15 November 2019 Available online 17 November 2019 0022-0248/ © 2019 Published by Elsevier B.V.
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
Fig. 1. Morphology of BPD etch pits in the substrate using the molten KOH at 500 for 30 min (a) and mechanism schematic of BPD converted TED in epitaxial growth (b).
growth, and the red circle marks are defined as the converted TEDs. It is found that converted BPDs present as a dislocation line ending at a write point, and propagate into epitaxial layer without write point in the topographic image. Meanwhile, the length of dislocation line for converted TEDs indicates the conversion of BPDs occurred in different thickness of an epitaxial layer. Fig. 3 shows the microscopy image of epitaxial wafer for 6 μm grown on 4° off-axis 4H-SiC substrate after molten KOH etching at 500 ℃ for 25 min (a) and 50 min (b). In the Fig. 3(a), the BPDs are not found. It is believed that the majority BPDs in the substrate are converted to relatively benign treading edge dislocations. Meanwhile, the origin of TEDs with in-grown or converted BPDs cannot be clearly distinguished in the epitaxial layer using the molten at 500 ℃ for 25 min. Subsequently, the same epitaxial layer is etched to 50 min and the microscopy image is shown in Fig. 3(b). With the increasing of etching time, the etching pits of surface in epitaxial layer become large compared to the Fig. 3(a). But their outlines are rounded hexagonal shape regardless of etching time. However, the etch pits of TEDs with different bottom morphology can be observed in the epitaxial layer, including the rounded hexagonal shape and shell shape. It is believed that the shell shape of TEDs bottom result from the conversion of BPDs in the substrate. Therefore, it is expected that the origin of TEDs in the epitaxial layer can be confirmed by deep KOH etching. To investigate the effect of growth temperature on the conversion of BPDs to TEDs during epitaxial growth, the various growth temperatures were executed at 20 ℃ lower than reference, reference and 40 ℃ higher than reference, respectively. As shown in the Fig. 4(a)–(c), the mapping distribution of BPDs in the epitaxial layers grown on different temperature is measured by using the optical surface analyzer with photoluminescence. The number of BPDs in epitaxial layer grown on high temperature is drastically increased. The BPD density of epitaxial layer is calculated and shown in Fig. 4(d). It is found that the almost free BPDs in epitaxial layer (＜0.01 cm−2) are obtained at the reference
the 4H-SiC substrate from the same ingot. The Synchrotron Monochromatic Beam X-ray Topography (SMBXT) studies were characterized to analyze the conversion of BPDs to TEDs during epitaxial growth. The BPDs density in epitaxial layer were measured using the optical surface analyzer (Lasertech: SICA 88). Meanwhile, in order to confirmed the correlation of same defect under different inspection, the samples were further etched by using the molten KOH at 500 ℃ and microscopy observation.
3. Results and discussion Fig. 1(a) shows the microscopy image of typical etch pit for dislocations on the 4° SiC substrate by using the molten KOH at 500 ℃ for 30 min. From the Fig. 1(a), it can be seen that the TEDs are hexagonal shape and the BPDs are shell shape with different directions, and the TSDs are not found in the area. The enlargement (inset) corresponding yellow dot line area shows that the feature of BPD is composed of two partials dislocations enclosing a stacking fault between them. It is well known that the step flow growth in down step direction and lateral growth perpendicular to the step flow direction can be simultaneously taken place during epitaxial growth [3,10]. In case of the step flow growth domination, the BPDs in substrate propagate into the epitaxial layer. On the contrary, the two sides of BPDs etch pits will come closer and merge, and the BPDs is converted to TEDs in the epitaxial growth. The mechanism schematic of BPDs converted TEDs is shown in the Fig. 1(b) during epitaxial growth. In order to investigate the conversion of BPDs in the substrate to TEDs during epitaxial growth, the dislocations of substrate and epitaxial layer (6 μm) for 4H-SiC are characterized by using the 〈11–28〉 reflection in grazing-incidence geometry, as shown in Fig. 2. Large or small bright spots and the dark line can be observed in the Fig. 2(a) and identified as TSDs, TEDs and BPDs, respectively [11]. Fig. 2(b) exhibits the morphology of BPDs taken from the same position after epitaxial
Fig. 2. SMBXT topography of BPDs in the 4H-SiC wafer. (a) substrate; (b) epitaxial wafer for 6 μm. 2
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
Fig. 3. Microscope images of an epi-layer grown on 4° off-axis 4H-SiC substrate after KOH etch at 500 ℃ for different time. (a) 25 min; (b) 50 min.
4. Conclusion
temperature. In addition, the lower BPD density can be also observed on the 20 ℃ lower than reference, but the large number of surface defects such as triangles, pits are found in the surface of epitaxial layer. It is believed that the effective C/Si ratio in the growth interface decrease significantly when the growth temperature is gradually increased at fixed C/Si ratio [12]. The growth mode of epitaxial growth depends strongly on the C/Si ratio. In the case of high C/Si ratio, the step flow growth is suppressed and the lateral growth is enhanced, leading to the high conversion rate of BPDs to TEDs. On the contrary, the conversion rate is decreased. However, a higher C/Si ratio can also induce a higher surface defect density because of 2D nucleation. Therefore, the high quality, low BPD epitaxial wafer can be obtained in a range of temperature
4H-SiC homoepitaxial layer is grown on 4° off-axis substrate by the traditional chemical vapor deposition. The growth temperature dependence of BPDs density in epitaxial layer is also investigated using the molten KOH etching and Synchrotron reflection X-ray topography observation. It is found that the majority BPDs are converted to TEDs in epitaxial process, and the origin of TEDs in epitaxial layer can be distinguished by the morphology difference of etch pits after deep KOH etching. The epitaxial layer with BPD density is successfully obtained as low as 0.01/cm−2 under lower temperature. It is well known that the lateral growth and step flow growth can be simultaneously taken place during epitaxial growth. If the lateral growth dominates, it is beneficial to enhance the conversion of BPDs to TEDs. As a result, the conversion
Fig. 4. BPDs distribution in epitaxial layer under various growth temperature. (a)-(c) mapping distribution and (d) density of BPDs in epitaxial layer with different growth temperature, respectively. 3
Journal of Crystal Growth 531 (2020) 125360
L. Yang, et al.
References
rate is decreased with the increasing of growth temperature. It is suggested that the effective C/Si ratio on the growth interface is decreased at high temperature, leading to the suppression of lateral growth during epitaxial process.
[1] [2] [3] [4] [5]
CRediT authorship contribution statement
[6]
L. Yang: Writing - original draft, Investigation, Visualization. L.X. Zhao: Conceptualization, Methodology, Formal analysis, Writing - review & editing. H.W. Wu: Data curation, Investigation.
[7] [8] [9] [10] [11]
Declaration of Competing Interest The authors declared that there is no conflict of interest.
[12]
4
F. La Via, M. Camarda, A. La Magna, Appl. Phys. Rev. 1 (3) (2014) 031301. Z. Zhang, T.S. Sudarshan, Appl. Phys. Letts. 87 (2005) 161917. H. Song, T. Sudarshan, J. Cryst. Growth 371 (2013) 94–101. R.E. Stahlbush, N.A. Mahadik, M.J. O'Loughlin, Mater. Sci. Forum 778–780 (2014) 309–312. R. Myers-Ward, B. VanMil, R. Stahlbush, S. Katz, J. McCrate, S. Kitt, C. Eddy, D. Gaskill, Mater. Sci. Forum 615–617 (2009) 105–108. T. Ohno, H. Yamaguchi, S. Kuroda, K. Kojima, T. Suzuki, K. Arai, J. Cryst. Growth 271 (2004) 1–7. H. Song, T. Rana, T. Sudarshan, J. Cryst. Growth 320 (2011) 95–102. B.L. VanMil, R.E. Stahlbush, R.L. Myers-Ward, K.-K. Lew, C.R. Eddy Jr., D.K. Gaskill, J. Vac. Sci. Technol., B 26 (2008) 1504–1507. L. Zhao, H. Wu, J. Cryst. Growth 507 (2019) 109–112. Z. Zhang, E. Moulton, T. Sudarshan, Appl. Phys. Lett. 89 (2006) 081910–81911. H. Wang, F. Wu, M. Dudley, B. Raghothamachar, G. Chung, J. Zhang, B. Thomas, E.K. Sanchez, S.G. Mueller, D. Hansen, M.J. Loboda, Mater. Sci. Forum 778–780 (2014) 328–331. S. Nishizawa, M. Pons, Chem. Vap. Deposition 12 (2006) 516–522.