SiC seed polarity-dependent bulk AlN growth under the influence of residual oxygen

Abstract

The structural properties of the heteroepitaxially grown AlN on off-axis 4H-/6H-SiC by PVT are presented in dependence of the seed polarity. In addition to long-term growth runs (48–72h) short-term experiments were carried out in order to investigate the initial growth stage. SEM, EDX, HR-TEM and HR-XRD studies show different growth modes for C-polar and Si-polar SiC seeds. The main cause is the anisotropic oxidation of SiC by Al2O(g) which is formed during heating up in the AlN source. The type of the growth mode is essential for the defect density in the grown bulk AlN crystal. The growth on C-polar SiC leads to a higher crystal quality of the bulk AlN with up to two orders of magnitude lower etch pit densities and smaller rocking curve widths and hence mosaicity compared to the growth on Si-polar SiC. New initial 3D island growth models for both seed polarities are introduced.