Improved Crystal Quality and Surface Morphology of Nonpolar a-plane GaN Grown on r-plane Sapphire Substrates

In this paper, we report on the improved crystal quality and surface morphology of nonpolar a-plane ([11-20]) GaN layers grown on r-plane ([1-102]) sapphire substrates by using a metal-organic chemical vapor deposition. Both the reactor pressure and the V/III ratio were modulated using two-steps during the growth in order to optimize the growth conditions for the fully coalesced GaN layers with smooth surfaces. As a result, a root-mean-square roughness of 0.678 rim was observed with atomic-force microscopy for the nonpolar a-plane GaN, and the full-widths at half-maximum values of the omega-rocking curve were 432 and 648 arcsec from the c- and the in-direction parallel scans, respectively. The low-temperature photoluminescence spectra were also investigated to identify the origin of the improvement in the crystallinity.