In this research we have used an inexpensive method to fabricate highly crystalline GaN nanowires (NWs) on porous zinc oxide (PZnO) on Si (1 1 1) wafer by thermal evaporation using commercial GaN powder, either in argon (Ar) gas atmosphere or a combination of Ar and nitrogen (N-2) gas atmosphere without any catalyst. Micro structural studies by scanning electron microscopy (SEM) and transmission electron microscope (TEM) measurements reveal the role of different gas flowing, in the nucleation and alignment of the GaN NWs. The GaN NWs different diameters ranging between 50 and 200 nm for the NWs grown under flow of mix gases, but the NWs which were grown under Ar gas only, have uniform diameter of around 50-60 nm, also their lengths are almost the same (around 10 mu m). Further structural and optical characterizations were performed using high resolution X-ray diffraction (HR-XRD), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. Results indicated that the NWs are of single-crystal hexagonal GaN with [0 0 0 1] and [1 0 (1) over bar 1] growth directions for NWs grown under Ar and mixed gas flow. (C) 2012 Elsevier B. V. All rights reserved.