Influence of oxygen partial pressure on the optical properties of β-Ga₂O_3-δ films deposited by pulsed laser deposition

High quality β-Ga₂O_3-δ films on c-sapphire substrates are deposited by pulsed laser deposition (PLD) under various oxygen partial pressures. The crystalline structure, chemometry and optical properties of the β-Ga₂O_3-δ films are investigated systematically by X-ray diffraction (XRD), far-infrared reflectance spectra, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible-near infrared (UV-vis-NIR) transmittance spectra. The XRD analysis shows that all the as-deposited films are of unique (-201) orientation. The transmittance spectra reveal that the films exhibit a high transparency above 80% in the UV-vis-NIR wavelength region above 255 nm (4.863 eV). Moreover, the optical constants and optical direct bandgap are extracted based on the transmittance spectra with Tauc-Lorentz (TL) dispersion function model and Tauc's relationship, respectively. A further step, the influence of oxygen partial pressure on optical properties is explained by theoretical calculation.