Type‐II Band Alignment in the β‐Ga ₂ O ₃ /Rutile GeO ₂ Heterojunction Toward Solar‐Blind Photodetection: A First‐Principles Study

Semiconductor heterostructures capable of separating photogenerated electrons and holes have a wide range of optoelectronic applications, including photodetectors, solar cells, and photocatalysts. β‐Ga 2 O 3 and rutile GeO 2 are both ultrawide‐bandgap semiconductors, with bandgaps of 4.85 eV and 4.68 eV, respectively, which have attracted increasing interest due to promising applications in next‐generation high‐power electronics and deep ultraviolet optoelectronics. Here, using first‐principles calculations, we investigate the interfacial property and band alignment of the β‐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 β‐Ga 2 O 3 /rutile GeO 2 interface, which facilitates the separation of photogenerated carriers. The valence band maximum of β‐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 an interfacial oxygen vacancy in the stable configuration leads to a reduction in the band offset. Our results suggest that the β‐Ga 2 O 3 /rutile GeO 2 heterojunction holds significant promise for application in strictly solar‐blind photodetectors.