Comparative Study of AlN Crystals Grown on SiC Seeds with/without Voids at the Heterointerface

AlN crystal growth on SiC seeds is an alternative approach for obtaining wafer-sized AlN crystals and has been demonstrated in experiments. Various characteristics of AlN crystals grown on SiC seeds were reported by different researchers, leading to complications in designing a reliable growth process. Here, we used comprehensive and comparative methods to reveal key factors affecting the characteristics of the AlN crystal. These include the initial SiC seed morphology evolved at the beginning of AlN crystal growth; in short, two typical morphologies were formed in the heterointerface between the SiC seed and AlN. One is AlN grown on a flat heterointerface, and the other is the AlN crystal developed from SiC pyramid islands formed due to the decomposition of the SiC seed under an AlN atmosphere. Such dissimilar interfaces result in differences in aspects such as the incorporated Si impurity content, strain, and uniformity of the grown AlN crystal. Significantly, a near-linear decrease in both the Si content (0.005%/μm) and the strain (represented by a Raman peak blue shift of 0.0084 cm–1/μm) with increasing AlN crystal thickness is found and well verified in a 1.1 mm-thick AlN crystal, which shows a narrow 112 arcsec full width at half-maximum in its (0002) X-ray rocking curve. Our results suggest that the AlN crystal grown on a flat SiC seed possesses more uniform physical properties, which are suitable for the growth of wafer-sized AlN crystals. The characteristics of AlN crystals grown on SiC seeds with/without voids at the heterointerface are studied comparatively, including a quantitative variation of Si doping contents, shift rates of the Raman peak position, and an fwhm of (0002), with increasing AlN crystal thickness. These results are important to understand the various phenomena observed in AlN crystals grown on SiC seeds.