Enhanced photodetection performance enabled by an out-of-plane built-in electric field

The photodetectors with low dark current, high sensitivity, and fast speed are of great importance to meet the requirement of high-speed and real-time visual perception scenarios. However, it still remains a significant challenge to achieve simultaneously all these performance metrics, particularly for the chemical vapor deposition (CVD) grown two-dimensional (2D) semiconductors that usually suffer from large trap states and low mobility. To address this challenge, we here propose an ultrasensitive phototransistor based on CVD-grown MoS2 film sensitized by an underneath WSe2 layer. By creating an out-of-plane built-in electric field at the vertical MoS2/WSe2 heterojunction, the photodetection performances, including dark current, sensitivity, and temporal response, are all improved due to the photo-gating effect. As a result, the dark current is much suppressed, and the ON/OFF ratio is significantly enhanced by two orders of magnitude, reaching 3.4 pA and 2.7 × 103, respectively, at Vg of −20 V. The temporal response also accelerates from the seconds to the milliseconds level due to an efficient photo-carrier separation by the vertical internal field. At Vg of 20 V, the responsivity (R) and detectivity (D*) are also improved by nearly three orders of magnitude, reaching up to 4.2 × 103 A W−1 and 1.8 × 1014 Jones, respectively, standing out among the state-of-the-art 2D based photodetectors. This work provides a universal and facile strategy to realize high performance photodetectors through an out-of-plane built-in electric field.