Type-II Band Alignment in the $\beta$-Ga${}_2$O${}_3$/Rutile GeO${}_2$ Heterojunction toward Solar-Blind Photodetection: A first-principles study

Abstract

Semiconductor heterostructures capable of separating photogenerated electrons and holes have a wide range of optoelectronic applications, including photodetectors, solar cells, and photocatalysts. $\beta$-Ga${}_2$O${}_3$ and rutile GeO${}_2$ are both ultrawide-bandgap semiconductors, with bandgaps of 4.85 eV and 4.68 eV, respectively. In this work, we employ first-principles calculations based on density functional theory to investigate the band alignment of the $\beta$-Ga${}_2$O${}_3$/rutile GeO${}_2$ heterojunction and explore the effect of interfacial oxygen vacancy. Calculations using the PBE0 hybrid functional based on an interface model show that a type-II band alignment emerges at the $\beta$-Ga${}_2$O${}_3$/rutile GeO${}_2$ interface, which facilitates the separation of photogenerated carriers. The valence band maximum of $\beta$-Ga${}_2$O${}_3$ lies 0.38 eV below that of rutile GeO${}_2$, and its conduction band minimum lies 0.36 eV below. The presence of interfacial oxygen vacancy in the stable configuration leads to a reduction in the band offset. Our results suggest that the $\beta$-Ga${}_2$O${}_3$/rutile GeO${}_2$ heterojunction holds significant promise for application in strictly solar-blind photodetectors.