Effects of a-plane sapphire substrate tilt angles on the growth behavior of nonpolar a-plane GaN

We investigated the effect of a slight tilt of an r-plane sapphire substrate on the morphological properties of a-plane GaN grown by using metal-organic chemical vapor deposition. The tilt angle of the r-plane sapphire was varied from 0° to -0.65° toward the c-axis of sapphire. Slight tilt angles of the r-plane sapphire toward the c-axis of sapphire ranging from 0° to -0.37° were found to be suitable for growing triangular pit-free a-plane GaN with a microscopically smooth surface. Tilt angles larger than -0.37° improved the crystalline quality in the direction of the m- axis of GaN but caused non-uniform growth and pit formation on the surface.