Growth of water-insoluble rutile GeO₂ thin films on (001) TiO₂ substrates with graded Ge x Sn1-x O₂ buffer layers

Rutile GeO 2 (r-GeO 2 ) is an ultrawide bandgap semiconductor with the potential for ambipolar doping and bulk single-crystal growth. In this study, we investigated r-GeO 2 thin films grown on (001) TiO 2 substrates with graded Ge x Sn 1− x O 2 buffer layers. GeO 2 grown on bare TiO 2 substrates via mist chemical vapor deposition exhibited water-soluble amorphous and/or α-quartz phases alongside the rutile phase. In contrast, the insertion of graded Ge x Sn 1− x O 2 buffer layers on the TiO 2 substrate allowed the growth of single-phase water-insoluble r-GeO 2 thin films. This study contributes to the development of water-insoluble r-GeO 2 thin films for various applications.