This paper presents the structural and optical studies of porous GaN prepared by ultra-violet (UV) assisted electrochemical etching under various conditions. The characteristics of the porous GaN samples were investigated by a variety of methods, including scanning electron microscopy (SEM), high resolution x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering. SEM images indicated that the average pore size was more sensitive to the concentration of the electrolyte as compared to the applied biasing. XRD measurements revealed that the hexagonal unit cell distortion of the porous samples was relatively small as compared to as grown sample. Both PL and Raman studies suggested that the porosity was capable of improving the lattice mismatch induced strain; however there was no strong relation between the average pore size and the degree of stress relaxation. PL measurements revealed that porosity-induced PL intensity enhancement was only found in certain porous samples; however, three additional strain-induced structural defect related PL peaks appeared in as grown sample were absent in all porous samples. Raman spectra showed the presence of two forbidden transverse optical modes in the porous samples which were not observed in the as grown sample. (c) 2006 Published by Elsevier B.V.