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

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.