Study of Optical Properties of MOCVD-Grown Rutile GeO2 Films
Abstract
Rutile germanium dioxide (r-GeO2) 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-GeO2 thin films grown on r-TiO2 (001) substrates via metal-organic chemical vapor deposition (MOCVD). Cathodoluminescence (CL) spectroscopy reveals broad visible emissions with distinct peaks near 470~nm and 520~nm. CL mapping indicates enhanced emission intensity in regions with larger crystalline domains, highlighting the correlation between domain size and optical quality. X-ray photoelectron spectroscopy (XPS) confirms the presence of Ge4+ 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-GeO2, reinforcing its potential for future applications in power electronics and deep-ultraviolet optoelectronic devices.
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