Effect of thickness on the structural and optical properties of the niobium-doped β-Ga2O3 films

To investigate the effect of thickness on the structural and optical properties of niobium-doped beta gallium oxide (β-Ga2O3:Nb) thin films, a series of β-Ga2O3:Nb thin films with different thicknesses were prepared by radio-frequency magnetron method. The crystalline quality is highly improved when the film thickness exceeds 145 nm. The surface exhibits different morphologies under different film thicknesses. The average transmittance of all the films are over 80% in visible range, and that the ultraviolet absorption edge shifts to longer wavelength indicates the bandgap shrinks with increasing the film thickness. Moreover, the photoluminescence spectrum measurements indicate that fewer defects were formed when the film thickness is around 145 nm.