Structural Evolution and Growth Mechanism of Self-Assembled Wurtzite Gallium Nitride (GaN) Nanostructures by Chemical Vapor Deposition

We present the fabrication of self-assembled wurtzite gallium nitride (GaN) nanostructures with manifold morphologies through chemical vapor deposition under controlled deposition conditions. The different nanostructures including vertical standing whiskered nanowires (NWs), entangled NWs, nanorods, micro/nanotowers, highly transparent ultrathin nanosheets, and hexagonal microcrystals were evolved by the direct reaction of metal Ga with NH3 using a self-catalytic process by varying the important growth parameters such as temperature, source to substrate distance, and the reactor pressure. The growth mechanism of GaN nanostructures with manifold morphologies was interpreted with a surface diffusion model by accounting the direct impingement and surface migration of adatoms. Electron microscopy studies combined with a selected area electron diffraction pattern recorded on the NWs show wurtzite structure with preferential growth direction of (0001). X-ray diffraction studies on different nanostructures show that the hexagonal GaN contains neither cubic GaN nor Ga2O3 phases. Room temperature photoluminescence spectra reveal high optical quality of the nanostructures grown under either equimolar ratio or slightly nitrogen-rich regime, and, interestingly, GaN microcrystals grown under Ga-rich conditions were dominated by the defect induced green and yellow luminescence.