Study of optical properties of MOCVD-grown rutile GeO ₂ films

Abstract Rutile germanium dioxide (r-GeO 2 ) is a promising ultra-wide bandgap (UWBG) semiconductor, offering a high theoretical Baliga figure of merit, potential for p-type doping, and favorable thermal and electrical properties. In this work, we present a comprehensive optical investigation of crystalline r-GeO 2 thin films grown on r-TiO 2 (001) substrates via metal-organic chemical vapor deposition. Cathodoluminescence spectroscopy reveals broad visible emissions with distinct peaks near 470 nm and 520 nm. X-ray photoelectron spectroscopy confirms the presence of Ge 4+ oxidation state and provides a bandgap estimation of ∼4.75 eV based on valence band and secondary electron cutoff analysis. UV–Vis transmittance measurements show a sharp absorption edge near 250–260 nm, corresponding to an optical bandgap in the range of 4.81–5.0 eV. These findings offer valuable insights into the defect-related emission behavior and band-edge characteristics of r-GeO 2 , reinforcing its potential for future applications in power electronics and deep-ultraviolet optoelectronic devices.