Optimizing the Stoichiometry of Ga 2 O 3 Grown by RF‐Magnetron Sputter Deposition by Correlating Optical Properties and Growth Parameters

β‐Ga 2 O 3 thin films are deposited by radiofrequency (RF)‐magnetron sputtering on quartz and c‐sapphire substrates using a ceramic stoichiometric Ga 2 O 3 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 Ga 2 O 3 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‐Ga 2 O 3 layer are identified. The main challenge in obtaining the stoichiometric β‐Ga 2 O 3 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‐Ga 2 O 3 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.