title: Role of metal contacts in high-performance phototransistors based on WSe2 monolayers.
abstract: Phototransistors based on monolayer transition metal dichalcogenides (TMD) have high photosensitivity due to their direct band gap transition. However, there is a lack of understanding of the effect of metal contacts on the performance of atomically thin TMD phototransistors. Here, we fabricate phototransistors based on large-area chemical vapor deposition (CVD) tungsten diselenide (WSe2) monolayers contacted with the metals of different work function values. We found that the low Schottky-contact WSe2 phototransistors exhibit a very high photo gain (10(5)) and specific detectivity (10(14)Jones), values higher than commercial Si- and InGaAs-based photodetectors; however, the response speed is longer than 5 s in ambient air. In contrast, the high Schottky-contact phototransistors display a fast response time shorter than 23 ms, but the photo gain and specific detectivity decrease by several orders of magnitude. Moreover, the fast response speed of the high Schottky-contact devices is maintained for a few months in ambient air. This study demonstrates that the contact plays an important role in TMD phototransistors, and barrier height tuning is critical for optimizing the photoresponse and photoresponsivity.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Chiu
authors.forename: Chang-Hsiao
authors.initials: CH
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li
authors.forename: Andrew Thye Shen
authors.initials: AT
authors.lastname: Wee