Plasmonic Au/Mo_xW_1-xS₂/Si Heterojunction for Broadband Photodetection

Alloying of 2D materials has emerged as a prevailing pathway to realize a tunable band gap with defect-engineered transition metal dichalcogenides (TMDs) for developing high-performance broadband photosensors. In this work, ternary 2D Mo_xW_1-xS₂ alloy nanosheets with various compositions were systematically synthesized through a facile hydrothermal route. Comprehensive structural and optical analyses confirm the formation of high-quality alloy nanosheets with compositionally tunable band gaps and improved optical characteristics. Anisotropic gold nanorods (AuNRs) were integrated with the alloy nanosheets on a 3D silicon platform, enabling efficient photocarrier generation via plasmonic enhancement. On the other hand, the built-in potential of the 2D alloy-Si mixed-dimensional heterojunction leads to rapid charge carrier extraction, thus resulting in enhanced broadband optical response. The AuNR-decorated Mo_0.5W_0.5S₂/Si hybrid device exhibits an excellent photo-to-dark current ratio (∼2000) and a responsivity of 7.88 A/W at 400 nm optical excitation. Synergistic effects from suppressed deep-level defect states in the alloy, the development of a strong built-in potential with the Si heterojunction, surface plasmon-enhanced robust light absorption and hot electron transfer might support enhancing the device performance, as additionally verified by computational methods. This work presents scalable synthesis of solution-processed TMD alloys for high-performance photodetector devices on the Si platform, paving the way for future CMOS-compatible 2D/3D photonics and next-generation optoelectronics.