Probing the peculiar emission behaviors of c-Sapphire wafer and β-Ga2O3/c-Sapphire via hard X-ray nanoprobe

Abstract

We report the intriguing phenomena of evolution of color centers (F and F⁺) using time-dependent X-ray excited optical luminescence (XEOL) in c-plane Sapphire wafer, β-Ga₂O₃/c-Sapphire and GaSe/β-Ga₂O₃/c-Sapphire. The increasing emission intensity of F⁺ and F-color centers over time indicates the formation of new color centers by continuous exposure to X-ray irradiation. These oxygen vacancy defect states remained even after having layer of epitaxial thin film of β-Ga₂O₃, and subsequent GaSe of sub μm thickness on top due to high penetration depth of X-ray. Interestingly, defect states of β-Ga₂O₃ decrease with time suggesting passivation of defect states induced by long term exposure to X-ray radiation. Also, we demonstrated the effect of long term X-ray irradiation using XEOL map, revealing spatial variation in defect state emission intensities. Time-resolved XEOL was used to measure dynamics of luminescence decay of F⁺ color center and defect state emission of Ga₂O₃.