Evolution of GaN nanowire morphology during catalyst-induced growth process

We report a very generic methodology to control the crystallographic orientation of GaN nanowires (NWs) in a chemical vapor deposition technique employing a standard vapor-liquid-solid mechanism. Incubation time was considered as a critical parameter to control the nanowire morphology. It was found that nanowires of a particular geometry, such as hexagonal, triangular, wurtzite/zinc-blende biphase, and square shaped forms could be obtained by varying the length of incubation time. The change in the diameter of the nanowires with respect to the size of the catalyst droplet was corroborated by a simple steady state model. Luminescence spectra recorded from the GaN NWs revealed the presence of a dominating wurtzite phase in all the as-grown samples. However, temperature independent behavior of two luminescence peaks, recorded especially from the biphase homostructure, was believed to originate from the radiative recombination of carriers localized at potential fluctuations in the zinc-blende and wurtzite phases discretely.