A Study on the Effect of Oxygen Flow Rate on Optical Properties of RF Sputtered a-GaOx Thin Films on Corning Glass Substrate

Transparent amorphous thin films of ultra-wide band gap (E-g approximate to 4.5-5.3 eV) gallium oxide (a-GaOx) were deposited on Corning glass substrates by radio frequency (RF) magnetron reactive sputtering under different oxygen flow rates. Amorphous nature of the deposited films was confirmed using X-ray diffraction method. Surface properties of the films were obtained from field emission scanning electron and atomic force microscopic images. Compositional and surface chemistry analyses were done using energy-dispersive X-ray and X-ray photoelectron spectroscopic techniques respectively. Optical characteristics of the films deposited under varying oxygen flow rates were investigated. UV-visible transmittance spectra showed excellent transparency in the visible region for all the films. Optical band gap values were found to increase with the increase of oxygen flow rates. Thickness of the films and refractive index dispersion relation were studied using spectroscopic ellipsometry by utilizing a Cauchy dispersion model. Refractive index dispersion parameters were obtained using Wemple-DiDomenico model. The results indicate that the presence of oxygen in the sputtering environment significantly alter the deposition rate and thereby optical properties of the films.