Photoinduced Schottky Barrier Lowering in 2D Monolayer WS2 Photodetectors

Arrays of metal-semiconductor-metal (MSM) photodetectors are fabricated using chemical vapor deposition (CVD) grown 2D monolayer WS2 as the absorbing semiconductor (WS2) with gold electrodes. A study of the channel length dependence (0.2-6.4 mu m) on the photoresponsivity and gain show substantial increase in performance is achieved when the length is reduced to 200 nm. A large gain factor of up to 480 is measured for 200 nm length devices and attributed to lowering of the Schottky barriers due to the filling of trapped states between the metal contact and WS2 by photogenerated carriers. Only photoexcited carriers close to the interface contribute to filling trap states and lowering the Schottky barrier and therefore increasing channel length only adds series resistance to the device that reduces performance. These results reveal detailed insights regarding the mechanisms for photocurrent generation in lateral MSM photodetectors that employ CVD grown monolayer WS2 material, which has important consequences for the commercial applications and large scale development of 2D imaging arrays.