Growth evolution and microstructural characterization of semipolar (1122) GaN selectively grown on etched r-plane sapphire

Semipolar (1122) GaN was grown on stripe etched r-plane sapphire substrate by a maskless selective growth method. The initial stage of growth is analyzed by describing the competitive nucleation mechanisms, due to the interplay between kinetics and energetics, on disparate crystallographic planes within the diffusion length of adatoms. The microstructure of the final coalesced semipolar GaN film is revealed by x-ray rocking curve (XRC) analysis and transmission electron microscopy (TEM). XRC analysis yields linewidths between 280 and 550 arcsec for all on-axis and off-axis diffractions. Linewidth broadening factors in dislocated crystals are considered, and a large reduction of stacking fault density can be seen from the measured linewidths as fit to this model. TEM shows a change in the defect characteristics as compared to conventional growth on m-sapphire, filtering of stacking faults and confirmation of the low dislocation density of the final GaN film. The microstructural quality of the film substantiates the possibility of using an inclined basal-plane growth to synthesize non-basal-plane active devices, thus removing the rigid restrictions in contemporary GaN nonpolar and semipolar heteroepitaxy.