Papers by Keyword: Polytype Transformation

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Authors: Krzysztof Grasza, Emil Tymicki
Abstract: Bulk crystals of 6H and 4H silicon carbide have been grown by PVT method. 6H-SiC were obtained in optimized near-to-equilibrium growth conditions in order to improve the crystal quality and to provide the 6H seeds for 6H to 4H-SiC conversion. In experiments of 6H to 4H polytype transformation a set of invariable growth conditions was applied: C-face seed, C-rich atmosphere, on-axis seed orientation, pre-heating of the source material, slightly convex crystallization front and optimized geometry of the growth system. Other growth parameters were varied to optimize the polytype conversion, e.g.: structural quality of the seed, intentionally added impurity (N and/or Sc), initial growth stage recipe, argon pressure and temperature gradient - resulting in variety of growth rates and temperatures of the seed. Special attention was paid to seed passivation and a scheme of temperature and inert gas pressure changes during growth. Crystals were characterized by KOH etching, X-ray diffraction, optical and AFM microscopy. A reproducible method of 75% efficient conversion was elaborated. A large central surface free of micropipes was observed with characteristic six symmetrical ridges as well as the increased concentration of nitrogen. The parasitic 15R-SiC polytype was nucleated on the vicinal part of the crystallization front of 6H-SiC and 4H-SiC crystals.
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Authors: B.J. Skromme, M.K. Mikhov, L. Chen, G. Samson, Rong Jun Wang, Can Hua Li, I. Bhat
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Authors: H. Takagi, Taro Nishiguchi, S. Ohta, Tomoaki Furusho, Satoru Ohshima, Shigehiro Nishino
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Authors: Emil Tymicki, Krzysztof Grasza, Katarzyna Racka, Tadeusz Łukasiewicz, Miroslaw Piersa, Kinga Kościewicz, Dominika Teklińska, Ryszard Diduszko, Paweł Skupiński, Rafał Jakieła, Jerzy Krupka
Abstract: In this work results of nitrogen doping in the amount of 0 vol.%, 3 vol.% and 10 vol.% on the growth of the 4H polytype on the 6H-SiC seed are presented. SiC crystals grown by PVT method on the (000-1) C-face of 6H seeds using the open seed backside design have been investigated. Structural and electrical properties of the crystals were studied by different experimental methods.
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Authors: Emil Tymicki, Krzysztof Grasza, Katarzyna Racka, Marcin Raczkiewicz, Tadeusz Łukasiewicz, Maciej Gała, Kinga Kościewicz, Ryszard Diduszko, Rafał Bożek
Abstract: In this work we present the growth of 4H-SiC crystals (2 inch in diameter) on the 8° off- axis C-face 6H-SiC seeds, inclined toward [11-20] direction. The growth of crystals by physical vapour transport method (PVT) was realized with the open seed backside in the experimental setup with graphite resistive heater. Some of the crystals were doped with cerium in the purpose of the 4H polytype growth stabilization. For Ce-doped crystals the seed backside carbonization process was decreased in comparison with such effect observed in the undoped SiC crystals.
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Authors: S. Harada, Yuji Yamamoto, Kazuaki Seki, Toru Ujihara
Abstract: Reduction of threading screw dislocation without polytype transformation from 4H-SiC was performed by the combination of step-flow growth and spiral growth. On a vicinal 4H-SiC seed crystal, threading screw dislocations are converted to Frank-type stacking faults by step-flow during solution growth. As the growth proceeds, the defects are excluded to the crystal. Thus utilizing the conversion, high quality SiC crystal growth without threading screw dislocations is expected to achieve. However, at the same time, polytype transformation is caused by the occurrence of 2D nucleation. By using the special shape of seed crystal, we successfully grew high quality 4H-SiC crystal without threading screw dislocation and polytype transformation.
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Authors: E.N. Mokhov, S.K. Obyden, A.D. Roenkov, G.V. Saparin, Yu.A. Vodakov
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Authors: Sang Il Lee, Jung Young Jung, Mi Seon Park, Hee Tae Lee, Doe Hyung Lee, Won Jae Lee, Soon Ku Hong, Im Gyu Yeo, Heung Rak Kim, Myong Chuel Chun
Abstract: SiC crystal ingots were grown on 6H-SiC dual-seed crystal with different surface properties by a PVT (Physical Vapor Transport) technique. And then SiC crystal wafers sliced from the SiC ingots were systematically investigated in order to find out the dependence of surface properties for seed on the polytype formation. While n-type SiC crystals exhibiting the 4H polytype were grown on seed crystal having high root-mean-square (rms) value, 6H-SiC crystals were grown on seed having lower rms value. However, 6H polytype was maintained on on-axis and off-axis seeds during the entire growth period. The crystal quality of 6H-SiC single crystals grown on on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on off-axis seed.
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Authors: Kenta Murayama, Tsukasa Hori, S. Harada, S. Xiao, M. Tagawa, Toru Ujihara
Abstract: In order to achieve a high-quality SiC crystal in solution growth, one of the most difficult issues is to grow a thick layer on Si face avoiding polytype transformation. In this case, two-dimensional nucleation, which leads to the polytype transformation, is frequently induced because a density of threading screw dislocations acting as a source of spiral step decreases and wide terraces form by step bunching as growth proceeds. Therefore, it is very difficult to stabilize the polytype of crystals grown with extremely low density of threading screw dislocations. In this study, we tried to overcome these problems by using specially designed seed crystal and optimizing growth temperature and temperature distribution. We successfully grew thick low-threading-dislocation density SiC crystal without polytype transformation under the condition of high growth temperature and homogeneous temperature distribution.
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Authors: Kazuaki Seki, Kai Morimoto, Toru Ujihara, Tomoharu Tokunaga, Katsuhiro Sasaki, Kotaro Kuroda, Yoshikazu Takeda
Abstract: 6H-SiC hetero-epitaxially grown on a (111) 3C-SiC was observed with TEM. High-density stacking faults were formed around the hetero-interface, and the density of stacking faults decreased with increasing distance from interface. On the other hand, when 3C-SiC was homo-epitaxially grown on a 3C-SiC, any stacking faults did not exist at the interface between the grown crystal and the seed crystal. Thus, the stacking faults formation started from the 6H/3C hetero-interface. Considering the lattice-mismatch strain between 3C-SiC and 6H-SiC, the strain energy is equivalent to the stacking fault energy of 6H-SiC. This similarity suggests that the stacking faults formation could be caused by the relaxation of the lattice-mismatch strain.
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