Janus monolayer MXY(M=Mo, W; X, Y=S, Se and Te)/β-Ga2O3 van der Waals heterojunctions with type I/II: A self powered UV to IR broad spectrum photodetector

High-performance self-powered photodetectors require strong built-in electric fields, faster response times, and broader response ranges. Monolayer β-Ga₂O₃, a promising material in the photodetector field, exhibits ultrahigh electron mobility, endowing it with high response speed and stability. However, its excessively large band gap weakens its absorption capacity in the infrared (IR) region, hindering its application in IR detection. We attempted to construct van der Waals heterojunctions using two-dimensional (2D) Janus materials to address these challenges. Therefore, we systematically investigated heterojunction systems composed of Janus MXY (X = S, Se, Te; Y =Mo, W) and Ga₂O₃ (100) surface by using first-principles calculations. It is found that the band gap of the heterojunctions is significantly reduced, forming typical Type-I/II band alignments that promote spatial separation of photogenerated electron hole pairs. All heterojunctions are thermodynamically stable, and we systematically screened out six direct band gap heterojunctions for further study based on their band structures. A large potential difference forms at the interface, generating a strong built in electric field that endows the heterojunctions with self powered capability. Optical calculations show that compared with pure Ga₂O₃, these heterojunctions exhibit approximately a 13 % increase in absorption coefficient in the ultraviolet (UV) region (60–100 nm) and significantly enhanced absorption in the infrared (IR) region. This study provides an important theoretical foundation for designing high performance Ga₂O₃-based self powered optoelectronic devices with broad spectral responses from UV to IR.