Spatially Bandgap-Graded MoS2(1−x)Se2x Homojunctions for Self-Powered Visible–Near-Infrared Phototransistors
Hao Xu, Juntong Zhu, Guifu Zou, Wei Liu, Xiao Li, Caihong Li, Gyeong Hee Ryu, Wenshuo Xu, Xiaoyu Han, Zhengxiao Guo, Jamie H. Warner, Jiang Wu, Huiyun Liu
Abstract
Abstract 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 ) Se 2 x alloys, 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 eV, leading to the formation of a homojunction with a built-in electric field. Consequently, a strong and sensitive gate-modulated photovoltaic effect is demonstrated, enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W −1 , a specific detectivity up to ~ 10 11 Jones, and an on/off ratio up to ~ 10 4 . 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 ~ 10 12 Jones, a photoconductive gain of 10 6 –10 7 , 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.