SiO 2 /SiC Interface Properties on Various Surface Orientations
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SiO2/SiC Interface Properties on Various Surface Orientations Hiroshi Yano1, Taichi Hirao2, Tsunenobu Kimoto2, and Hiroyuki Matsunami2 1 Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan. 2 Department of Electronic Science and Engineering, Kyoto University, Yoshidahonmachi, Sakyo, Kyoto 606-8501, Japan. ABSTRACT The _interface properties of MOS capacitors and MOSFETs were characterized using the _ _ (0001), (1120), and_(0338) faces of 4H-SiC. (0001) and (1120) correspond to (111) and (110) in cubic structure. (0338) is semi-equivalent to (100). The interface states near the conduction band edge are discussed based on the capacitance and conductance _measurements of n-type MOS capacitors at a low temperature and room temperature. The (0338) face indicated the smallest interface state density near the conduction band edge and highest channel mobility in n-channel MOSFETs among these faces. INTRODUCTION Although SiC power MOSFETs have received much expectation to realize ultra-low-loss high-speed switching devices, a low channel mobility (typically < 10 cm2/Vs) in the MOS inversion channel brings a high channel resistance and limits the device performance. The low channel mobility is attributed to a high density of interface states, especially near the conduction band edge in 4H-SiC. Therefore one of the most important issues to realize high-performance SiC power MOSFETs is improvement of the MOS interface quality (enhancement of the channel mobility and reduction of the interface state density). Most of the MOS-related research works have been done using (0001) Si-face materials with several degrees off-angle. In 1999, we have 2 found that a higher _ channel mobility (~100 cm /Vs) can be obtained for 4H-SiC MOSFETs by utilizing the (1120) face[1-3] instead of the conventional (0001) face (~5 cm2/Vs). From the investigation of the temperature dependence of the channel mobility and threshold voltage[2,4], _ MOS interface _properties on (1120) and (0001) were found to be quite different. The channel mobility on (1120) showed the negative temperature dependence of ~T -2.2, while that on (0001) showed the positive temperature dependence of ~T 2.6. The threshold voltage on (0001) decreased with increasing temperature due to emission of trapped electrons from interface states, _ whereas that on (11 2 0) was insensitive to the temperature. We have also found that the distribution of interface state_ density depends on the surface orientations[5,6]. The (0001) and (1120) faces of hexagonal crystal structure correspond to the (111) and (110) faces of cubic structure, respectively. In the case of Si, it is well known that the (100) face has the smallest interface state density[7]. Then, we thought that there may exist other surface orientations that can improve interface properties further. Although the origin of interface states may be different, we have selected a new surface orientation of 4H-SiC that has similar surface _ atom arrangement to (
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