Whiskered GaN nanowires by self-induced VLS approach using chemical vapor deposition

Abstract

We report the fabrication of whiskered GaN nanowires (NWs) by self-catalytic assisted vapor-liquid-solid approach using chemical vapor deposition. The growth is initiated by the pre-deposition of a Ga metal droplet layer followed by the reaction of NH₃ under nitrogen rich conditions to promote GaN nucleation for the subsequent growth of NWs. The NWs are straight, long, non-entangled and free from the tapering effect. The average diameter of the NWs is 150 nm and length varies up to few tens of micrometers. Despite having a high growth velocity, we observed a diameter dependent growth rate of GaN NWs. The length of the wires shows a linear dependence with reciprocal diameter. Nanowires with larger diameter grow slowly and thinner wires rapidly under the influence of diffusion induced growth mechanism. High resolution transmission electron microscopy with selected area electron diffraction shows that the NWs are wurtzite, single crystalline and free from defects. Micro-Raman spectrum recorded on the back scattering geometry reveals the presence of forbidden surface optical modes at 621.5 and 672.4 cm⁻¹ due to the break in optical wave vector along with the symmetry allowed E₂^H, A₁(TO) and A₁(LO) phonon modes. Low temperature photoluminescence recorded for the ensembles of NWs shows a strong free donor bound exciton peak at 3.461 eV in addition to the characteristics of yellow band of GaN.