Improved crystal quality of non-polar a-plane GaN epi-layers directly grown on optimized hole-array patterned r-sapphire substrates

Abstract

The characteristics of a-plane GaN films directly grown on silicon dioxide (SiO₂) hole-array patterned r-sapphire substrates (HPSS) were investigated in this work. Various pattern sizes of SiO₂ HPSS were prepared to obtain fully coalescent a-plane GaN films with high crystalline quality. The anisotropic behavior and crystalline quality characterized by X-ray diffraction (XRD) were significantly improved in a-plane GaN grown on optimized micro-HPSS (MHPSS) of 3 μm pattern with 1 μm diameter, in which the X-ray rocking curve-full width at half maximum (XRC-FWHM) values were 513 arcsec along the m-axis and 531 arcsec along the c axis. Scanning electron microscopy (SEM) results suggested that the presence of the SiO₂ mask might influence the dominant fast-growing facets. The different sizes of patterns governed the lateral growth length of a-plane GaN islands, which increased the mosaic size along the m direction and eliminated the anisotropic behavior. In addition, the modified Williamson–Hall (W–H) analysis showed that the density of basal stacking faults (BSFs) was reduced by an order of magnitude in a-plane GaN using MHPSS, as compared with a-plane GaN grown on planar r-sapphire. This work provides a simple and effective method without interruption and regrowth to solve two important problems in a-plane GaN, in which not only was the anisotropic behavior almost eliminated, but also the BSF density was greatly reduced.