Gate-tunable trion switch for excitonic device applications

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  • Sarthak Das
  • Sangeeth Kallatt
  • Nithin Abraham
  • Kausik Majumdar

Trions are excitonic species with a positive or negative charge, and thus, unlike neutral excitons, the flow of trions can generate a net detectable charge current. Trions under favorable doping conditions can be created in a coherent manner using resonant excitation. In this work, we exploit these properties to demonstrate a gate controlled trion switch in a few-layer graphene/monolayer WS2/monolayer graphene vertical heterojunction. By using a high-resolution spectral scan through a temperature controlled variation of the band gap of the WS2 sandwich layer, we obtain a gate voltage dependent vertical photocurrent strongly relying on the spectral position of the excitation, and the photocurrent maximizes when the excitation energy is resonant with the trion peak position. Further, the resonant photocurrent thus generated can be effectively controlled by a back gate voltage applied through the incomplete screening of the bottom monolayer graphene, and the photocurrent strongly correlates with the gate dependent trion intensity, while the nonresonant photocurrent exhibits only a weak gate dependence-unambiguously proving a trion driven photocurrent generation under resonance. We estimate a sub-100 fs switching time of the device. The findings are useful towards demonstration of ultrafast excitonic devices in layered materials.

Original languageEnglish
Article number081413
JournalPhysical Review B
Volume101
Issue number8
Number of pages7
ISSN2469-9950
DOIs
Publication statusPublished - 27 Feb 2020

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