We investigated the effects of SiNx interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiNx layer could strongly affect the a-plane GaN surface morphology due to the different SiNx coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiNx coverage and multiple SiNx-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiNx interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.
We investigated the structural and optical characteristics of nonpolar a-plane (11-20) GaN structure grown on TiO2 nanoparticles (NP)-coated r-plane sapphire by spin coating method. The surface morphology without any observable
inverse pyramidal pits was observed by atomic force microscopy (AFM) measurement. Transmission electron
microscopy (TEM) analysis revealed that the threading dislocations (TDs) and basal plane stacking faults (BSFs)
densities were around 4.5 × 109 cm-2 and 3.1 × 105 cm-1, respectively. It was also found that the broadening of x-ray
rocking curves (XRC) full width at a half maximum (FWHM) in Si-doped a-plane GaN on the TiO2 NP-coated r-plane
sapphire was affected by the tilt and twist of mosaic crystals. The photoluminescence (PL) intensity of TiO2 NP-related
MQWs sample at 295 K was approximately 18 % higher than that of the reference sample. This implied that the improved PL intensity was attributed to scattering of light by TiO2 NP and InGaN/GaN MQWs interface of high quality.