The microstructure of GaN nucleation layers grown by MOCVD on (1120) sapphire versus pressure and temperature

In this work, the evolution of morphology and defect structure in GaN nucleation layers on the a-plane of sapphire are investigated using TEM. The growth temperature and pressure were varied from 560 to 1100°C and from 20 to 600 torr, respectively. Whereas the highest growth temperature leads to a continuous layer, a 2D growth mode is not attained when the chamber pressure is varied from 20 to 600 torr at 1028°C. At the highest pressures (>300 t orr), a large distribution is obtained for the island sizes.