Effect of vicinal off-cut substrates on the basal stacking fault density in nonpolar a-GaN epilayers

Joint effect of miscut r-plane sapphire substrate and different nucleation layers on structural characteristics of non-polar a-plane GaN films

“…5 However, due to the large lattice mismatch between the r -plane sapphire substrate and a -plane GaN film (1.1% and 16.1% along the c -axis and m -axis respectively of the a -plane GaN film), high-density crystal defects such as stacking faults and partial misfit dislocations originated from the hetero-interface can be generated, leading to severe deterioration of crystalline quality. 6,7 The intense in-plane strain induced by a large difference in the lattice constant and thermal expansion coefficient between the r -plane sapphire substrate and a -plane GaN epitaxial layer can also result in cracks on the surface and the generation of crystal defects in the a -plane GaN film. 8 Several studies have been conducted to improve the crystalline quality of the GaN film by using SiN x interlayers, 9 patterned sapphire substrates, 10 epitaxial lateral overgrowth technique, 11 growth temperature optimization, 12 ammonothermal growth on HVPE-GaN seeds, 13 and ultra-high-pressure annealing treatment.…”

“…17 In particular, direct epitaxial growth of a non-polar a -plane GaN film on a miscut r -plane sapphire substrate (MRSS) has been proven to be a facile, contamination-free, and helpful process for improvement of surface morphology and the reduction in misfit dislocation density of a -plane GaN films. 6,18 However, the effects of the variation in the nucleation layer (NL) deposited over the MRSS on the structural characteristics of the a -plane GaN film have not been investigated. Moreover, optimization of the miscut angle of the MRSS for the epitaxial growth of a -plane GaN films has not been performed.…”