Wafer-scale selective area growth of GaN hexagonal prismatic nanostructures on c-sapphire substrate 322

Selective area growth of GaN nanostructures has been performed on full 2 00 c-sapphire substrates using Si 3 N 4 mask patterned by nanoimprint lithography (array of 400 nm diameter circular holes). A new process has been developed to improve the homogeneity of the nucleation selectivity of c-oriented hexagonal prismatic nanostructures at high temperature (1040 1C). It consists of an initial GaN nucleation step at 950 1C followed by ammonia annealing before high temperature growth. Structural analyses show that GaN nanostructures are grown in epitaxy with c-sapphire with lateral overgrowths on the mask. Strain and dislocations are observed at the interface due to the large GaN/sapphire lattice mismatch in contrast with the high quality of the relaxed crystals in the lateral overgrowth area. A cathodoluminescence study as a function of the GaN nanostructure size confirms these observations: the lateral overgrowth of GaN nanostructures has a low defect density and exhibits a stronger near band edge (NBE) emission than the crystal in direct epitaxy with sapphire. The shift of the NBE positions versus nanostructure size can be mainly attributed to a combination of compressive strain and silicon doping coming from surface mask diffusion. Introduction......Page 1 Single-step temperature growth......Page 2 Two-step temperature growth......Page 3 Selectivity versus growth temperature......Page 4 Optical studies of single nanostructures......Page 5 Conclusions......Page 6 References......Page 7