Spatially Bandgap-Graded Mo S(2(1-x))Se2x Homojunctions for Self-Powered Visible–Near-Infrared Phototransistors

Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features, which opens up new potential for device applications. Here, visible–near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS(2(1-x))Se2xalloys, synthesized by a simple and controllable chemical solution deposition method, are reported. The graded bandgaps, arising from the spatial grading of Se composition and thickness within a single domain, are tuned from 1.83 to 1.73 e V, leading to the formation of a homojunction with a builtin electric field. Consequently, a strong and sensitive gate-modulatedphotovoltaic e ect is demonstrated, enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 m A W-1, a specific detectivity up to ～ 1011Jones, and an on/o ratio up to ～ 104. Remarkably, when illuminated by the lights ranging from 405 to 808 nm, the biased devices yield a champion photoresponsivity of 191.5 A W-1, a specific detectivity up to ～ 1012Jones, a photoconductive gain of 106–107, and a photoresponsive time in the order of ～ 50 ms. These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p–n junctions.