Microstructural studies of GaN grown on (0001) sapphire by MOVPE

A transmission electron microscopy (TEM) study of GaN samples grown by metalorganic vapor phase epitaxy (MOVPE) on (0001) sapphire at different stages of the growth process is presented. The low temperature (600 °C) buffer layer which is required for high quality GaN, exhibits a mixed hexagonal-cubic polycrystalline microstructure. After a short annealing at higher temperature (1050 °C), cubic islands remain on its top surface. The microstructure of the epilayers could be separated in two zones. Close to the interface with sapphire, misfit dislocations, basal stacking faults and ‘nanocavities’ are present. After a thickness of 0.5 μm, two types of threading defects remain: edge dislocations with 1/3〈11–0〉 Burger vector and nanopipes.