Nucleation of GaN on (0001) sapphire during MOCVD growth: an atomic force and high resolution electron microscopy study

摘要

The morphology and microstructure of GaN nucleation layers have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The nucleation layers were grown at 500°C by metalorganic chemical vapour deposition (MOCVD) on (0001) sapphire. Different deposition times were used in order to investigate the evolution of the nucleation layer and try to understand the growth mechanisms. Systematically, it was found that the thinnest layers are mainly defect free and have a cubic structure. The (111) GaN planes are parallel to (0001) sapphire. It is shown that the nucleation follows the Volmer-Weber mechanism and as the islands height increases, the transformation from cubic to wurtzite starts from the substrate surface.