Photogating WS2 Photodetectors Using Embedded WSe2 Charge Puddles

• Published in: ACS nano Vol. 14; no. 4; pp. 4559 - 4566
• Main Authors: Tsai, Tsung-Han, Liang, Zheng-Yong, Lin, Yung-Chang, Wang, Cheng-Chieh, Lin, Kuang-I, Suenaga, Kazu, Chiu, Po-Wen
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.04.2020
• Subjects: TMD; 2D material; heterostructure; photogating; photodetector; WS2
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.0c00098

Performance of 2D photodetectors is often predominated by charge traps that offer an effective photogating effect. The device features an ultrahigh gain and responsivity, but at the cost of a retarded temporal response due to the nature of long-lived trap states. In this work, we devise a gain mechanism that originates from massive charge puddles formed in the type-II 2D lateral heterostructures. This concept is demonstrated using graphene-contacted WS2 photodetectors embedded with WSe2 nanodots. Upon light illumination, photoexcited carriers are separated by the built-in field at the WSe2/WS2 heterojunctions (HJs), with holes trapped in the WSe2 nanodots. The resulting WSe2 hole puddles provide a photoconductive gain, as electrons are recirculating during the lifetime of holes that remain trapped in the puddles. The WSe2/WS2 HJ photodetectors exhibit a responsivity of 3 × 102 A/W with a gain of 7 × 102 electrons per photon. Meanwhile, the zero-gate response time is reduced by 5 orders of magnitude as compared to the prior reports for the graphene-contacted pristine WS2 monolayer and WS2/MoS2 heterobilayer photodetectors due to the ultrafast intralayer excitonic dynamics in the WSe2/WS2 HJs.