Structural and electrical anisotropies of Si-doped a-plane (11-20) GaN films with different SiN_x interlayers

The effects of different SiN_x interlayers on the structural and electrical properties of nonpolar Si-doped a-plane (11-20) GaN films grown on r-plane (1-102) sapphire were investigated. The surface roughness depends strongly on the SiN_x coverage, deposition temperature and number of SiN_x layers. The in-plane anisotropy of on-axis x-ray rocking curves (XRCs) (full width at half-maximum) was significantly decreased by the introduction of multiple SiN_x-treated GaN interlayers, indicating coherently scattering domains of uniform size. Off-axis XRC measurements were also employed to investigate the effects on the mosaic twist corresponding to edge dislocation and the I₁-type basal-plane stacking fault (BSF) density. Hall effect measurement showed that the electrical conductivity was the highest when multiple SiN_x/GaN interlayers were employed. The measured sheet resistances (R_sh) along the c-axis were higher than those along the m-axis. These anisotropic conductivities could be explained by BSFs acting as carrier scattering centers. The ratios of R_sh along the two in-plane orientations also correlated well with the BSF densities.