Effect of nucleation time on GaN layer grown on different shapes of patterned sapphire substrate

In this work, GaN layer was grown on patterned sapphire substrate (PSS) with the shape of cone-patterned sapphire substrate (CPSS) and dome-patterned sapphire substrate (DPSS) at different nucleation times. The nucleation time was varied at 40 and 80 seconds. The results showed that the nucleation islands were bigger with nucleation time for the growths on CPSS and DPSS. With bigger islands, the GaN layer evenly coalesced, which in turn, reduced the dislocation density as well as surface roughness in and of the overgrown GaN layer. Nonetheless, the results were better for the GaN grown on DPSS in comparison to the GaN layer grown on CPSS. The reason was associated to the curvature of the dome patterns, which was more slanted than cone patterns, and thereby, resulting in smoother surface of nucleation on the sidewalls. Hence, the multiple growth orientations were less promoted in comparison to the growth on CPSS.