Effects of growth temperature and thickness on structure and optical properties of Ga2O3 films grown by pulsed laser deposition

A series of Ga2O3 films grown on sapphire substrate by pulsed laser deposition with different growth temperature (400-1000 degrees C) and different thickness (69-332 nm) were studied by X-ray diffraction, optical transmittance and spectroscopic ellipsometry. The phase was transformed from amorphous to polycrystalline beta-Ga2O3 structure with increasing growth temperature. Refractive indexes increase with increasing thickness or growth temperature of the films in the transparent area, where the effect of film thickness is much more significant than that of growth temperature. The Urbach tail observed in absorption edge by ellipsometry combined with the transmittance spectra and the XRD intensities illustrate that higher growth temperature or thicker thickness can improve the crystal quality of films. The band gap of Ga2O3 films decrease with increasing growth film thickness and elevated experimental temperature (25-600 degrees C), and the quantitative analysis of temperature-dependent band gap was conducted by using the Varshni equation.