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 degrees C) buffer layer which is required for high duality GaN, exhibits a mixed hexagonal-cubic polycrystalline microstructure. After a short annealing at higher temperature (1050 degrees 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 slacking faults and 'nanocavities' are present. After a thickness of 0.5 mu m, two types of threading defects remain: edge dislocations with 1/3[<11(2)over bar 0>] Burger vector and nanopipes. (C) 1997 Elsevier Science S.A.