Effect of SiC‐on‐Si template residual stress on GaN residual stress and crystal quality

The thermal expansion coefficient mismatch between GaN and SiC is lower than between GaN and Si. However it is usually observed that GaN on SiC/Si templates has higher tensile stress than GaN directly on Si. To provide an insight into the relationship between SiC template residual stress and GaN overlayer residual stress and crystal quality, we have analyzed the in-plane residual stress gradient present in GaN/SiC microstructure arrays of various dimensions and shapes using micro-Raman spectroscopy. It was found that the GaN overlayer residual stress is directly proportional to the SiC buffer layer residual stress. GaN films with lower residual stress also resulted in GaN films with improved crystal quality. Our study shows that the frequently encountered problems of high tensile stress in GaN films deposited on SiC templates is due to the high tensile residual stress in the SiC layers. The poorer GaN crystal quality deposited on SiC templates reported in literature is also likely due to the high tensile stress in the SiC templates. In order to grow GaN films with sufficient compressive stress and crystal quality for subsequent device processing, it is crucial to reduce the high tensile stress present in the SiC templates. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim