Negative Photo-Response Switching via Electron-Hole Recombination at The Type Iii Junction of MoTe 2 Channel/SnS 2 Top Layer.

Extensive study on two-dimensional (2D) van der Waals heterojunctions has primarily focused on PN diodes for fast-switching photo-detection, while achieving the same from 2D channel phototransistors has been rare despite their other advantages. Here, we have designed a high-speed phototransistor featuring a type III junction between p-MoTe 2 channel and n-SnS 2 top layer. Our photo-detecting device operates with a basis of negative photo-response (NPR), which originates from the recombination of photo-excited electrons in n-SnS 2 and accumulated holes in the p-MoTe 2 channel. For the NPR to occur, high-energy photons capable of exciting SnS 2 (band gap ∼2.2 eV) have been found to be effective, because lower-energy photons simply penetrate the SnS 2 top layer only to excite MoTe 2 , leading to normal positive photo-response (PPR) which is known to be slow due to the photo-gating effects. Our NPR transistor showcases 0.5 ms-fast photo-responses and a high responsivity over 5000 A W -1 . More essentially, such carrier recombination mechanism is clarified with three experimental evidences. The phototransistor is finally modified with Au contact on n-SnS 2 , to be a more practical device displaying voltage output. Three different photo-logic states under blue, near infra-red (NIR), and blue-NIR mixed photons are demonstrated using the voltage signals. This article is protected by copyright. All rights reserved.