Low-Pressure Chemical Vapor Deposition Growth of Rutile GeO2 on Sapphire

An emerging ultra-wide energy bandgap (UWBG) semiconductor, rutile GeO2, has taken great interest due to having 4.68 eV energy bandgap, bipolar dopability, acceptable electron and hole mobility and thermal conductivity. The synthesis of r-GeO2 through various growth techniques is still in the early stages of development. There is a strong demand for high crystal quality r-GeO2 at low cost, achievable through scalable growth techniques that utilize benign sources and generate non-hazardous by-products. Here, we report the growth conditions of low-pressure chemical vapor deposition of r-GeO2 on sapphire substrates using GeO as the precursor to grow (101) r-GeO2 on a-plane sapphire. The effects of growth temperature, Ge source temperature, O2 and Ar flow rates, and system pressure were systematically investigated. At optimal growth conditions, relatively smooth (101) r-GeO2 film was obtained at a growth rate of 0.96 µm/hr (0.48 µm thick) with a (101) r-GeO2 ω-scan FWHM of 839 arcsec. We have also achieved suppression of quartz (hexagonal) phase island growth via low growth temperature (<625 °C), high O2 flow rates (>50 sccm) and high growth pressure (>30 Torr). This study establishes LPCVD growth conditions for the heteroepitaxial growth of r-GeO​2 on low-cost sapphire substrates, paving the way for its applications in high-power electronics and solar-blind photodetectors.