Establishment of a growth route of crystallized rutile GeO2 thin film (≧1 μm/h) and its structural properties

Abstract

Recently, rutile germanium dioxide (r-GeO2) has emerged as a novel ultra-wide bandgap semiconductor due to its theoretical excellent properties, that is, high thermal conductivity, ambipolar dopability, and high carrier mobility, in addition to its wide bandgap (4.44-4.68 eV). In this study, r-GeO2 thin films were grown on (001) r-TiO2 substrates by mist chemical vapor deposition. To optimize the growth conditions, we analyzed the decomposition processes of the Ge source (C6H10Ge2O7) by thermogravimetry-differential thermal analysis. It is found that GeO2 was synthesized from C6H10Ge2O7 at 553-783 °C in aqueous vapor. We accomplished fabrication of (001)-oriented r-GeO2 on r-TiO2 with a growth rate of 1.2-1.7 μm/h. On the other hand, under lower growth rate conditions (50 nm/h), the full width at half maximum of the r-GeO2 002 peak remarked a relatively small value of 560 arc sec. In addition, clear diffraction spots of r-GeO2 and r-TiO2 were observed at the r-GeO2/r-TiO2 interface, and the film was found to be significantly strained along the in-plane direction (∼2.3%) by cross-sectional transmission electron microscopy. The growth rate of ≧1 μm/h must contribute to the fabrication of thick r-GeO2 films, which can be utilized as power electronics devices with high breakdown voltage.