Analysis of the nucleation of GaN layers on (0001) sapphire

Low temperature nucleation of GaN on (0001) sapphire is investigated. Depositions were made for 20–180 s at 560 °C by metalorganic chemical vapour deposition (MOCVD). It is shown that the shortest deposition times give rise to the formation of crystallites with the sphalerite structure. Subsequently, the density and the size of nucleation islands increase and they start to transform to wurtzite from the interface with the substrate. From the start, the nuclei contain misfit dislocations. Calculations of residual relaxations done on GaN islands for the 60 and the 120 s nucleation layers, respectively, show that the 120 s nucleation is probably more relaxed.