We investigated the effects of SiN<sub>x</sub> interlayers on the structural and electrical properties of nonpolar <i>a</i>-plane (11-20) GaN grown on <i>r</i>-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiN<sub>x</sub> layer could strongly affect the <i>a</i>-plane GaN surface morphology due to the different SiN<sub>x</sub> coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the <i>a</i>-plane GaN samples with high SiN<sub>x</sub> coverage and multiple SiN<sub>x</sub>-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 SiN<sub>x</sub> interlayers. The anisotropy of sheet resistance between the <i>c</i>-and <i>m</i>-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.
The thick GaN layers were grown on GaN/Si(111) templates by hydride vapor phase epitaxy (HVPE). The GaN templates were grown by metal organic chemical vapor deposition (MOCVD), and there were remained some cracks on their layers. The silicon (Si) substrates were not treated any patterning process. The size of template was 2inch Si(111) wafer and these templates were directly used for HVPE growth. For the growth of the thick GaN layer, the gas injection system of HVPE was modified for improving its growth rate. The proper growth temperature and V/III ratio gave us a transparent thick GaN layer and its thickness has been over than 100um for 2 hours. After the growth, the Si substrate was etched by Si etching solution. We obtained a transparent thick GaN layer and its size was 1/4 inch as the biggest size and it was bended. Structural and optical properties of thick GaN layer were characterized by high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) measurements.