Growth behavior of GaN nanoneedles with changing HCl/NH3 flow ratio

We grew one-dimensional GaN nanoneedles on AlN/Si(111) substrates at HCl/NH3 gas-flow ratios of 1/20, 1/30, and 1/50 using the hydride vapor-phase epitaxy (HVPE) method. Field emission-scanning electron microscopy (FE-SEM) images of GaN nanoneedles show that the vertical growth rate of GaN nanoneedles increases with increasing gas-flow ratio, but there is little growth in the lateral direction. X-ray diffraction patterns indicate that GaN nanoneedles grew with c-axes oriented perpendicular to the substrate. The room-temperature PL spectrum of GaN nanoneedles was detected at 3.237 eV of near-band-edge transitions.