Improvement in a-Plane GaN Crystal Quality by Investigating Different Buffer Layer

Abstract

Non-polar a-plane GaN epitaxial layer was grown on r-plane sapphire substrates by metal–organic chemical vapor deposition (MOCVD). In this paper, we implanted different buffer layer, including the GaN buffer layers under different growth parameters and in situ SiNx layer, to improve the crystal quality. First, high growth temperature (1150 °C) of GaN buffer layer can improve the crystal quality than low temperature (540 °C) by scanning electron microscopy (SEM) images. The inverse pyramidal pits are also reduced by implanting in situ SiNx interlayer, behaving as a nanomask deposited on r-plane sapphire. The GaN film quality is also improved by growing GaN buffer layer under low V/III ratio and confirmed by high-resolution X-ray diffraction (HR-XRD). An improvement of crystal quality through initial surface roughening can be verified by atomic force microscopy (AFM). The rms roughness of the overlaying GaN surface can be reduced from 11.82 to 1.54 nm. The growth mechanism was discussed.