Wet chemical passivation of n-GaN surface was carried out by dipping GaN samples in ammonium sulphide diluted in aqueous and alcoholic solvent base solutions. Photoluminescence (PL) investigations indicated that sulphide solution effectively led to the reduction of GaN surface states. Increased band edge PL peak showed that S2- ions are more active in alcohol based solvents. X-ray photoelectron spectroscopy revealed reduction in surface oxides by introduction of sulphide species. Ni/n-GaN Schottky barrier diodes were fabricated on passivated surfaces. Remarkable improvement in the Schottky barrier height (0.98 eV for passivated diodes as compared to 0.75 eV for untreated diodes) has been observed. (C) 2013 Elsevier B.V. All rights reserved.