Fabrication and characterization of tilted R-plane sapphire wafer for nonpolar a-plane GaN

Tilt angle of r-plane wafer is a one of the important factors related with the quality of the GaN epi, so the fine control of the tilt angle is important for the growing of high quality non-polar a-GaN epi. We prepared the R-plane sapphire wafers with slight tilt angles for nonpolar a-plane GaN. The target tilt angles of alpha and beta were 0, -0.1, -0.15, -0.2, -0.4, -0.6 degrees and -0.1, 0, 0.1 degrees, respectively. The tilt angles of sliced R-plane sapphire wafers were measured by x-ray and the statistical evaluation of reliability of tilt angles of wafers were performed. The tolerance of the tilt angle was +/- 0.03 degrees. R-plane sapphire wafers have relatively large distributions of BOW and TTV data than c-plane sapphire wafers due to the large anisotropy of R-plane. As the tilt angle a was increased from -0.1 to -0.6 degrees, the step widths and heights were decreased from 156 nm to 26 nm and 0.4 nm to 0.2 nm, respectively. The growth and qualities of GaN epi seems to be largely affected by the change of step structure of R-plane sapphire wafers with tilt angle.