Electronic Structure of Noncentrosymmetric α-GeO2 with Oxygen Vacancy: Ab Initio Calculations and Comparison with Experiment

Polycrystalline alpha-GeO2, space group P3(2)2I, has been prepared by low-temperature chemical synthesis. alpha-GeO2 electronic structure has been evaluated comparatively by X-ray photoelectron spectroscopy (XPS) and ab initio calculations. The oxygen vacancies have been formed in alpha-GeO2 by Ar+ ion bombardment at ion energy 2.4 keV. The appearance of oxygen-vacancy-induced new states in the band gap has been detected by XPS and theoretical analysis. It has been shown that oxygen monovacancy generation provides defect states in the valence band, in the band gap, and in the conduction band.