Structural evolution of GaN nucleation layers during metal-organic chemical vapour deposition growth

Low temperature nucleation of GaN on (0001) sapphire is investigated. Depositions were made for 20 s, 40 s, 60 s, 120 s and 180 s at 500°C by MOCVD. It is shown that the shortest deposition times give rise to the formation of small cubic crystallites. Subsequently, the density of nucleation islands increases, they grow in height and their shape is modified. They start to transform to wurtzite from the interface with the substrate. These results will be discussed in terms of the operating nucleation and growth mechanisms.