Papers by Author: Emi Makino

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Authors: Hiroki Yamaguchi, Yukinori Sakiyama, Emi Makino, Shoichi Onda, Yoichiro Matsumoto
Abstract: The origin of the polytypes of SiC has been investigated from the viewpoint of surface reactions by the density functional theory (DFT) within the Projector Augmented Wave-Generalized Gradient Approximation. Three radicals were considered here as the major species in the crystal growth process: Si, Si2C and SiC2. We supposed that these radicals contribute to the crystal growth directly through the adsorption on the 4H-SiC (000-1) C-face surface. The DFT calculations showed that the Si2C, which relatively has a similar structure with the SiC crystal, had no activation barrier to be adsorbed chemically to the 4H-SiC C-face surface. On the other hand, SiC2 with Si showed an activation barrier of 0.79eV to form the 4H-SiC crystal. In order to investigate the arrangements to decide polytypism in SiC, we compared the adsorption energies between the different sites, which correspond to the 4H-SiC crystal and a disordered arrangement. The activation energies had almost no difference. Our calculations indicated that these radicals do not contribute to the origin of the polytypes of SiC.
Authors: Hideyuki Tsuboi, Megumi Kabasawa, Seika Ouchi, Miki Sato, Riadh Sahnoun, Michihisa Koyama, Nozomu Hatakeyama, Akira Endou, Hiromitsu Takaba, Momoj Kubo, Carlos A. Del Carpio, Yasuo Kito, Emi Makino, Norikazu Hosokawa, Jun Hasegawa, Shoichi Onda, Akira Miyamoto
Abstract: The main electronic characteristics of silicon carbide (SiC) are its wide energy gap, high thermal conductivity, and high break down electric field which make of it of one of the most appropriate materials for power electronic devices. Previously we reported on a new electrical conductivity evaluation method for nano-scale complex systems based on our original tight-binding quantum chemical molecular dynamics method. In this work, we report on the application of our methodology to various SiC polytypes. The electrical conductivity obtained for perfect crystal models of 3C-, 6H- and 4H-SiC, were equal to 10-20-10-25 S/cm. For the defect including model an extremely large electrical conductivity (of the order of 102 S/cm) was obtained. Consequently these results lead to the conclusion that the 3C-, 6H-, and 4H-SiC polytypes with perfect crystals have insulator properties while the electrical conductivity of the crystal with defect, increases significantly. This result infers that crystals containing defects easily undergo electric breakdown.
Authors: Jun Kojima, Yuichiro Tokuda, Emi Makino, Naohiro Sugiyama, Norihiro Hoshino, Isaho Kamata, Hidekazu Tsuchida
Abstract: In order to diffuse the use of SiC, mass-production technologies of SiC wafers are needed. It is easy to be understood that high-speed and long-sized growth technologies are connected directly with mass-production technologies. The gas source growth method such as HT-CVD has the possibilities and the potential of the high-speed and long-sized growth. In this article, it was clarified that the high growth rate were achieved by the control of the source gas partial pressures and by the gas boundary layers. The average growth rate was 1mm/h on the f4 inch-diameter crystal, and the maximum growth rate reached 3.6 mm/h on the 12.5x25 mm tetragon by the above gas control. The crystal qualities of the gas source methods were also evaluated the equivalent level in comparison with the sublimation method. Concerning the 1mm/h-growth f3 inch crystal, the densities of TSDs were kept in the 102 cm-2 levels from the seed to the upper-side of the ingot. Moreover, the ingot size increased year by year and a f4 inch x 43 mm sized ingot has been developed.
Authors: Isaho Kamata, Norihiro Hoshino, Yuichiro Tokuda, Emi Makino, Jun Kojima, Hidekazu Tsuchida
Abstract: This paper reports on evidence of high-quality and very fast 4H-SiC crystal growth achieved using a high-temperature gas source method. The formation of threading screw dislocations (TSDs) during crystal growth was examined by comparing synchrotron X-ray topography images taken for a seed and grown crystals, while the generation of a high density of new TSDs is observed under improper growth condition. High-quality crystal growth retaining the TSD density of the seed crystal was accomplished under an improved condition, even for a very high growth rate of 2.1 mm/h.
Authors: Isaho Kamata, Norihiro Hoshino, Yuichiro Tokuda, Emi Makino, Naohiro Sugiyama, Jun Kojima, Hidekazu Tsuchida
Abstract: This paper investigates the quality of 4H-SiC crystals grown at a very fast growth rate (> 2.5 mm/h) using a high-temperature gas source method. Differences in nitrogen doping efficiency were clarified in facet and step-flow regions. In case for growth in the macro-step bunching mode, doping fluctuation and void formation were observed in the macro-step bunching region. Propagation of threading screw dislocations (TSDs) in the grown crystal was also investigated by synchrotron X-ray topography.
Authors: Hidekazu Tsuchida, Isaho Kamata, Masahiko Ito, Tetsuya Miyazawa, Norihiro Hoshino, Hiroaki Fujibayashi, Hideki Ito, Masami Naitou, Hirofumi Aoki, Koichi Nishikawa, Emi Makino, Yuichiro Tokuda, Jun Kojima
Abstract: This paper introduces our recent challenges in fast 4H-SiC CVD growth and defect reduction. Enhanced growth rates in 4H-SiC epitaxial growth by high-speed wafer rotation and in a high-temperature gas source method promoting SiC bulk growth by increasing the gas flow velocity are demonstrated. Trials and results of deflecting threading dislocations by patterned C-face 4H-SiC epitaxial growth are also shown.
Authors: Norihiro Hoshino, Isaho Kamata, Yuichiro Tokuda, Emi Makino, Jun Kojima, Hidekazu Tsuchida
Abstract: Possibilities of very fast 4H-SiC crystal growth using a high-temperature gas source method are surveyed by computational simulation and experimental studies. The temperature range suitable to obtain high growth rates are investigated by simulating temperature dependences of growth rates for H2+SiH4+C3H8 and H2 +SiH4+C3H8+HCl gas systems. Simulation and experimental results demonstrate that an increase in source gas flow rates as well as gas-flow velocities enhance growth rates. High growth rates exceeding 1 mm/h are experimentally obtained using both gas systems. Single crystal growth on a 3-inch diameter seed crystal is also demonstrated.
Authors: Jun Kojima, Emi Makino, Yuichiro Tokuda, Naohiro Sugiyama, Notihiro Hoshino, Hidekazu Tsuchida
Abstract: This article gives the results of crystal growth by a High-Temperature Gas Source Method such as HTCVD. It was reported that clusters were formed and were an important factor of the growth in HTCVDs, and some influences of them were investigated. The difference between the model with and without clustering was compared. The experimental growth rates corresponded to the cluster model, and this indicated that clusters affect the crystal growth. Relations between the experimental growth rate and the growth temperature as a function of gas flow ratio were investigated. The gas flow ratio was defined: (SiH4+C3H8) / (SiH4+C3H8+H2). Maximum growth rate was 2.3mm/h under high source gas ratio. At present, a Φ75mm×54mm sized ingot has been developed.
Authors: Norihiro Hoshino, Isaho Kamata, Yuichiro Tokuda, Emi Makino, Naohiro Sugiyama, Jun Kojima, Hidekazu Tsuchida
Abstract: Limitations in the very fast growth of 4H-SiC crystals are surveyed for a high-temperature gas source method. The evolution of macro-step bunching and void formation in crystal growth is investigated by changing the partial pressures of the source gases and crystal rotation speeds. The variation in macro-step formation depending on radial positions, where step-flow or spiral growth governs, of a grown crystal is also revealed. Based on the relation between growth conditions and macro-step bunching, a trade-off between growth rate enhancement and crystal quality and a method to improve such trade-off are discussed. Nitrogen at a high concentration under very high growth rates in the high-temperature gas source method is also investigated.
Authors: Hiromitsu Takaba, Ai Sagawa, Miki Sato, Seika Ouchi, Yuko Yoshida, Yukie Hayashi, Emi Sato, Kenji Inaba, Riadh Sahnoun, Michihisa Koyama, Hideyuki Tsuboi, Nozomu Hatakeyama, Akira Endou, Momoj Kubo, Carlos A. Del Carpio, Yasuo Kito, Emi Makino, Norikazu Hosokawa, Jun Hasegawa, Shoichi Onda, Akira Miyamoto
Abstract: The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C > H > Si > SiC2 > Si2C > C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.
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