Effect of pulsed ion-beam treatment on the electronic and optical properties of GaN epitaxial films on sapphire

Abstract

GaN films epitaxially grown on sapphire substrates and stored for more than a year under normal conditions were treated using pulsed mixed carbon-hydrogen ion beam. The electronic structure transformations of GaN on sapphire samples were studied using X-ray photoelectron spectroscopy (XPS), optical absorption, photoluminescence and density functional theory (DFT)-based simulations after such treatment. Weak acidification in the form of Ga—N…O was revealed by XPS method for both as-grown and ion-irradiated GaN on sapphire samples. GaN decomposition and Ga-loss effects were not detected after pulsed ion-beam treatment (PIBT), either experimentally or theoretically. It was shown that PIBT promotes a narrowing of the bandgap, changes the vacancy concentration in the surface region, and provides hydrogenation of the surface with the formation of hydroxyl groups in nondefective areas of the surface and near surface layers. PIBT-induced densification of the layers is observed due to annealing of vacancies; no detectable changes in the surface area morphology were found. The weak shift of the valence band edge corresponds to the contribution from areas with more nitrogen defects. The presence of these states in the bandgap could be the possible source of an increase in the electro and photocatalytic activity of GaN epitaxial films.