Centimeter-Scale Two-Phase Mixed Re_0.58Mo_0.42S₂ Grown via Low-Pressure Chemical Vapor Deposition and Its Heterostructure with GaSe for High-Performance Photodetectors

Two-dimensional (2D) Re_xMo_1–xS₂ ternary transition-metal dichalcogenides are attracting increasing attention because their bandgap and conductivity are tunable, and their conductivity type can be switched from n-type to p-type through phase engineering, enabling applications in photodetection and photocatalysis. However, a high density of grain boundaries in 2D Re_xMo_1–xS₂ films strongly scatters carriers and degrades the photodetector performance. Here, we address this limitation by constructing a Re_0.58Mo_0.42S₂/GaSe heterostructure, in which exfoliated 2D GaSe flakes, as a high-quality carrier transport layer, are dry-transferred and inserted between Re_0.58Mo_0.42S₂ and the metal electrodes. Re_0.58Mo_0.42S₂ with a thickness of 2.5 nm and a lateral size up to 1 cm was grown on mica by low-pressure chemical vapor deposition (LPCVD). The film exhibits a mixed crystal structure of 1T’ and 2H phases, which are p-type and n-type, respectively. The 1T’/2H interface forms a p–n junction that promotes separation of photogenerated carriers, while the band alignment in the heterostructure drives hole transfer to GaSe, thereby improving carrier separation and transport. The Re_0.58Mo_0.42S₂/GaSe photodetector achieves a responsivity (R) of 840 A/W, an external quantum efficiency (EQE) of 2.32 × 10⁵%, a specific detectivity (D*) of 1.10 × 10¹⁰ Jones, and a rise/decay time of 3 ms/1 ms, outperforming devices based solely on Re_0.58Mo_0.42S₂ or GaSe. These results demonstrate that heterostructures based on two-phase mixed ternary semiconductors are promising for high-performance photodetection.