[MoB3] Crystal Growth & Characterization of Oxides

2:45 PM - 3:00 PM JST(5:45 AM - 6:00 AM UTC)

[MoB3-03] Stabilization of Rutile GeO₂ by Graded Ge_xSn_1-xO₂ Buffer Layers

〇Kazuki Shimazoe¹, Kazutaka Kanegae², Hiroyuki Nishinaka², Masashi Kato¹ (1. Nagoya Inst. Tech. (Japan), 2. Kyoto Inst. Tech. (Japan))

Rutile-structured germanium dioxide (r-GeO₂) is a promising ultrawide bandgap semiconductor for high-power switching devices owing to its ultrawide bandgap (4.68 eV), ambipolar doping ability, and the availability of bulk substrates. However, its heteroepitaxial growth is hindered by phase separation induced by lattice mismatch. This study investigated the stabilization of r-GeO₂ on (001) TiO₂ substrates using graded Ge_xSn_1-xO₂ buffer layers to reduce lattice mismatch. Mist chemical vapor deposition was employed for the growth of thin films. The Ge ratios in the precursor solutions for the graded buffer layer ranged from 70% to 95% in increments of 5%, enabling a gradual reduction in the lattice mismatch. X-ray diffraction 2θ-ω scans revealed a significant enhancement in the (002) r-GeO₂ peak intensity with the graded buffer layer. Field-emission scanning electron microscopy combined with water-immersion tests confirmed that the graded buffer layer suppressed the water-soluble amorphous and α-quartz phases. Electron backscatter diffraction further verified the single-phase r-GeO₂ growth on the graded buffer layer. These results demonstrate that graded Ge_xSn_1-xO₂ buffer layers effectively suppress phase separation and stabilize the rutile phase, highlighting the importance of lattice mismatch for control of the GeO₂ polymorph.