Tunable Optical Properties of Amorphous-Like GaO Thin Films Deposited by Electron-Beam Evaporation with Varying Oxygen Partial Pressures.

GaO thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10 Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the GaO films was analyzed using sophisticated techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet-visible spectroscopy and a laser-induced damage test system. The correlation between the oxygen partial pressure and the film's properties in optics and materials were investigated. XRD and Raman revealed that all films were amorphous in spite of applying a varying oxygen partial pressure. With the change of oxygen partial pressure, XPS data indicated that the content of oxygen in the GaO films could be broadly modulable. As a result, a changeable refractive index of the GaO film is realizable and a variable blue-shift of absorption edges in transmittance spectra of the films is achievable. Moreover, the damage threshold value varied from 0.41 to 7.51 J/cm according to the rise of oxygen partial pressure. These results demonstrated that the optical properties of GaO film can be broadly tunable by controlling the oxygen content in the film.