Zinc Dopant-Induced Modulation of Electronic Structure and Defect Emissions in Monoclinic Gallium Oxide

Zinc (Zn) is a promising dopant for inducing visible emissions in monoclinic gallium oxide (beta-Ga2O3); however, the recombination mechanism of these emissions is unclear. Here, the effect of the Zn dopant on the valence-band electronic structure and luminescence properties of nanocrystalline beta-Ga2O3 films is investigated through chemical and optical analyses as well as density functional theory (DFT) simulations. The comparison between the DFT results and the photoemission spectra of the valence band and core levels shows the accuracy and consistency of structure optimization. The undoped beta-Ga2O3 film exhibits a broad emission band consisting of two emission bands: ultraviolet (UV) at 3.3 eV and blue luminescence (BL) at 2.9 eV, characteristic of pure beta-Ga2O3. Incorporation of Zn into the beta-Ga2O3 film significantly changes the luminescence spectral line shapes, resulting in an additional green luminescence (GL) band at 2.45 eV alongside the characteristic UV and BL emissions, which are found to be strongly dependent on excitation energy. Furthermore, the simulation of the spectral line shapes of these emission bands from the Zn-doped film within the framework of the configuration-coordinate model reveals the intraband states responsible for these luminescence bands and their electron-phonon coupling strengths. The simulation results show that the UV, BL, and GL emissions can be attributed to the self-trapped hole, V-Ga, and Zn-Ga acceptor states, and their energy levels are found to be 0.6, 1.1, and 1.5 eV above the valence band, respectively.