WS2/WSe2 Nanodot Composite Photodetectors for Fast and Sensitive Light Detection
ACS APPLIED ELECTRONIC MATERIALS(2021)
摘要
Owing to the exotic optical properties, semiconducting transition metal dichalcogenides (TMDs) have been targeted for sensitive photodetection with a high gain. Yet, it remains a challenge to achieve fast response dynamics while retaining a high responsivity. In this work, we demonstrate a 2D composite photodetector comprising of graphene-contacted monolayer WS2 stacked atop dispersed WSe2 nanodots. Upon light illumination, excess photoexcited electrons are generated and drift to a WS2 channel due to the type-II band alignment at the WS2/WSe2 heterojunction, leaving photoexcited holes in WSe2 nanodots. Recirculation of electrons across the WS2 channel provides a photogain during the lifetime of holes that remain trapped in WSe2 nanodots. The composite photodetector can reach a high responsivity of 8.4 x 10(2) A/W with a gain of 2.0 x 10(3) electrons per photon and, meanwhile, a fast response time in a few milliseconds. It also exhibits a high detectivity of 9.7 x 10(11) Jones and an on-to-off current ratio of 10(5). This performance enhancement is ascribed to the devised concept of using CVD-grown WSe2 nanocrystals as a photosensitizer, which reduces the contact barrier by WSe2-nanodot photodoping and provides rapid excitonic dynamics through the size-controllable WSe2/WS2 heterojunction.
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关键词
transition metal dichalcogenides, WS2, nanodots, photodetector, heterojunction, fast response
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