Optimizing the Stoichiometry of Ga2O3 Grown by RF-Magnetron Sputter Deposition by Correlating Optical Properties and Growth Parameters

Abstract

β-Ga2O3 thin films are deposited by radiofrequency (RF)-magnetron sputtering on quartz and c-sapphire substrates using a ceramic stoichiometric Ga2O3 target and a constant flux of argon process gas. Oxygen flux, heater power, and sputtering power are varied in the synthesis of the layers. The resulting Ga2O3 layers are analyzed in terms of their structural and optical properties. Based on this analysis, the process parameters leading to the formation of an optimized β-Ga2O3 layer are identified. The main challenge in obtaining the stoichiometric β-Ga2O3 thin films by sputter deposition is to overcome the influence of a strong preferential sputtering of Ga from the ceramic target. This can be achieved by adding a suitable fraction of oxygen to the argon process gas used in the deposition process. Furthermore, it is demonstrated that the refractive index dispersion of β-Ga2O3 depends strongly on its composition. Thus, a combined analysis of refractive index dispersion and optical bandgap position may serve as a valuable preliminary probe of the thin film's composition.