Understanding the effects of annealing induced structural transformations on the UVC absorbance and other optical properties of RF sputter deposited Ga2O3 thin films

Abstract

Gallium oxide (Ga2O3) is a transparent material with high absorption in the UVC region of the electromagnetic spectrum and hence is a very important candidate in the field of short wavelength optical device fabrication. A proper understanding of the different optical parameters is necessary for developing more efficient coatings and devices. In this work, changes in the optical behavior of Ga2O3 thin films due to post-deposition annealing (at temperatures 300 °C–900 °C) are discussed in detail. Structural, surface morphological and compositional modifications of the films are identified using the x-ray diffractometer, scanning electron microscopy and x-ray photoelectron spectrometer techniques, respectively. At 900 °C, a highly stable monoclinic β phase of Ga2O3 is obtained. The optical transmittance spectra acquired using UV–Vis spectroscopy indicate an improved UVC absorbance of the β-Ga2O3 films with an excellent visible transmittance (>80%). The structural transformation from amorphous to crystalline β-Ga2O3 phase and the associated reduction in defect density is found to modify other optical attributes, like the bandgap energy, Urbach energy, dispersion parameters, etc.