Epitaxial Growth of High Quality SiC by Sublimation Close Space Technique with High Growtn Rate

CST法是在由源极、衬底和石墨隔离层构成的狭窄空间内，通过升华和扩散转移促进生长。该方法与传统的SiC体材料升华方法基本相同。配置的一个大的区别是源和衬底之间的距离。我们使用高纯度的3C-SiC多晶板作为源，在2200-2400 ℃的温度范围内实现了高生长，其生长速度约为40-200 μ m/h。由生长速率与温度的关系求得活化能为147 kcal/mol。通过在衬底上引入偏角，在较宽的温度范围内获得了镜面形貌。还观察到台阶聚束，台阶的迹线宽度约为5 μ m。在晶体生长过程中观察到沿沿着方向有线状阴影的缺陷<1120>，表明晶体生长遵循阶梯流动机制。表面形态通常受到许多参数的影响，例如间隔物高度。当垫片高度降低时，出现波纹状图案。当高度增加时，表面变得相当光滑。Ta片也用于避免来自坩埚壁的不需要的碳物质。在适当的条件下，可以得到非常光滑的表面，但Ta的碳化是获得高质量SiC外延层的关键参数。在涂钽坩埚中制备外延层，得到台阶聚束自由表面。在光致发光测量中，施主-受主对发射被大大抑制。在光致发光测量中，观察到与中性N施主结合的激子有关的RO线和SO线。这意味着外延层是高质量的。这些线是特别观察到的具有高生长速率（例如大于100 μ m/h）的外延层。这表明，提高生长速率可能有助于降低掺杂到外延层中的杂质浓度。我们制作的肖特基二极管击穿电压为40 V，没有边缘端接。

In CST method, growth is promoted by sublimation and diffusion transfer in a narrow space which is constructed by source, substrate and graphite spacer. This method is basically same as conventional sublimation method for SiC-bulk. One big difference of configuration is the distance between source and substrate. We used 3C-SiC polycrystalline plate with high purity as source and High growth was achieved at a temperature range of 2200-2400ﾟC, and it was around 40-200 mu m/h. Activation energy obtained by temperature dependence of the growth rate was l47kcal/mol. By introducing off-angle to the substrate, a mirror-like morphology was obtained in the wide temperature range. Step bunching was also observed and trace width of the step was about 5 mu m. A defect having line shaped shadow was observed along <1120> direction, and it indicates that crystal growth followed step-flow mechanism. Surface morphology is often affected by many parameters such as spacer height. When the spacer height decreased, wavy pattern appeared. When the height increased, rather smooth surface appeared. Ta-sheet was also used to avoid unwanted carbon species from the wall of crucible. Appropriate condition, very smooth surface was obtained, however, carbonization of Ta seems a key parameter to get high quality SiC epilayer. Epilayer made in Ta pasted crucible, step-bunching free surface was obtained. Donor-acceptor pair emission was greatly suppressed in the photoluminescense measurement In this photoluminescence, RO and So lines, which is related excitons bound to neutral N donors, were observed. It means epitaxial layers are of high quality. These lines were especially observed epitaxial layers with high growth rate such as more than 100 mu m/h. It indicates that increasing growth rate may be useful to decrease impurity density doped into epitaxial layers. We made Schottky diodes showed breakdown voltage of 40V without edge termination.