Photoinduced Schottky Barrier Lowering in 2D Monolayer WS₂ Photodetectors

Abstract

Arrays of metal-semiconductor-metal (MSM) photodetectors are fabricated using chemical vapour deposition grown 2D monolayer WS2 as the absorbing semiconductor (WS2) with gold electrodes. A study of the channel length dependence (0.2-6.4 µm) on the photoresponsivity and gain show substantial increase in performance is achieved when the length is reduced down to 200nm. A large gain factor of up to 480 is measured for 200nm 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.

Ultrathin 2D Photodetectors Utilizing Chemical Vapor Deposition Grown WS2 With Graphene Electrodes

“…15,24,47,48 However, similar gate dependence of Schottky barrier height were not observed in our WS2 devices with Au electrodes (Supporting Information S3), which could be due to Fermi level pinning attributing to the existence of trap states at the Au-WS2 interface, discussed in our previous work. 49 To explain the light modulated photoresponsivity, we turn to the photoinduced charge transfer in graphene/WS2 heterostructure which has been observed in a previous study. 23 This surface charge transfer process generates layer-separated electron-hole pairs, with electrons residing in graphene and holes located in WS2, resulting in the n-doping of graphene (Fig- ure 6c).…”

2D WS2: From Vapor Phase Synthesis to Device Applications

“…[ 202 ] The contact barrier can as well be lowered under light luminescence for short channel photodetectors. [ 27 ] Remarkably, only the photo‐carriers near the contact interface would contribute to fill the traps states and lower the Schottky barrier. In this case, the longer channel length adds additional series resistance to photodetectors, leading to reduced device performance (Figure 25d).…”

“…achieved a high photoresponsivity of 20 A W −1 under a large source–drain bias (4 V) for monolayer WS 2 photodetectors. [ 27 ] Originating from the good flexibility of monolayer WS 2 , it is also suitable for flexible photodetectors. Lan et al.…”

“…It has the relatively high carrier mobility, [ 22 ] large exciton binding energy, [ 23 ] large spin–orbit splitting, [ 24 ] and strong photoluminescence (PL). [ 25 ] These properties make it idle for a wide range of applications, such as transistors, [ 26 ] photodetectors, [ 27 ] light‐emitting devices (LEDs), [ 28 ] etc. Despite the fact that there are numerous reports focused on the synthesis, properties, and applications of 2D WS 2 , there is still a lack of the comprehensive review on 2D WS 2 .…”

Material and Device Architecture Engineering Toward High Performance Two-Dimensional (2D) Photodetectors

“…Typical 2D layered semiconductors usually have their own distinct band gaps. The contact resistance at the electrode/semiconductor interface is often a dominating factor in the case of optoelectronic devices [89][90][91]. Meanwhile, the local electric field enhancements in devices can improve photoresponse.…”