An Asymmetry Field‐Effect Phototransistor for Solving Large Exciton Binding Energy of 2D TMDCs

Abstract

The probing of fundamental photophysics is a key prerequisite for the construction of diverse optoelectronic devices and circuits. To date, though, photocarrier dynamics in two-dimensional materials remains unclear, plagued primarily by two issues: a large exciton binding energy, and the lack of a suitable system that enables the manipulation of excitons. Here, we demonstrate a WSe2-based phototransistor with an asymmetric split-gate configuration, which we name the asymmetry field-effect phototransistor (AFEPT). This structure allows for the effective modulation of the electric field profile across the channel, thereby providing a standard device platform for exploring the photocarrier dynamics of the intrinsic WSe2 layer. By controlling the electric field, we observed in this work the spatial evolution of the photocurrent, notably with a strong signal over the entire WSe2 channel. Using photocurrent and optical spectroscopy measurements, we clarified the physical origin of the novel photocurrent behavior and determined a room temperature exciton binding energy of 210 meV with our device. In our phototransistor geometry, lateral p-n junctions serve as a simultaneous pathway for both photogenerated electrons and holes, reducing their recombination rate and thus enhancing photodetection. Our study establishes a new device platform for both fundamental studies and technological applications. © 2022 Wiley-VCH GmbH This article is protected by copyright. All rights reserved