Influence of controlled growth rate on tilt mosaic microstructures of nonpolar a-plane GaN epilayers grown on r-plane sapphire

The influence of the epitaxial growth rate on the surface morphology, as well as the crystallinity and optical properties of nonpolar a-plane GaN epilayers grown on r-plane sapphire substrate, has been investigated by x-ray diffraction and photoluminescence studies. The a-plane GaN epilayer grown at faster growth rates revealed a horizontal-pillar-shaped morphology with triangular-pits having sharp corners. While the epilayer grown at a faster growth rate showed a greater difference in the ω tilt-offset angle and line-width value between the on- and off-axes from x-ray diffraction, the a-plane GaN grown at the relatively slower growth rate showed a flat morphology with few pits and small ω tilt-offset difference. Growth of nonpolar a-plane GaN epilayer was optimized, and the effect of the growth rate of the a-plane GaN epilayer and the reason for the difference in the ω tilt-offset line-width value between the c- and m-direction mosaicity of x-ray diffraction were analyzed.