Bipolar Tunable Field-Effect Transistor Based on the <i>T</i>_d-MoTe₂/WSe₂ Heterojunction with Reconfigurable Polarity Transition for Enhanced Photodetection

Broadband photodetectors based on a two-dimensional (2D) heterojunction have received tremendous attention in recent years and have broad application potential in biochemical analysis, optical communication, and other fields. The photodetectors based on the asymmetric Schottky junction have demonstrated attractive optoelectronic properties due to their ultralow dark current and improved photodetection properties. However, it is difficult to tune the Schottky barriers with 2D semiconductors due to the Fermi pinning effect or the large mismatch between the energy band structure of the 2D channel and the metal electrode. Herein, we demonstrate a broadband photodetector based on semimetal Td-MoTe2/bipolar semiconductor WSe2/Ti covering the visible-to-infrared wavelength. Kelvin probe force microscopy characterization reveals a well-matched energy band alignment between Td-MoTe2 and WSe2 that allows the Schottky barriers to be broadly modulated by the gate voltage, leading to a reconfigurable polarity transition of the photocurrent. The spatially resolved photocurrent mapping indicates that the asymmetric junction at both ends dominates the photocurrent generation at the different bias voltages. The gate voltage is applied to change the Fermi level of WSe2, which modulates the Schottky barrier and, thereby, improves carrier transport and photoelectric conversion capabilities. As a result, the device achieves a 417% improvement in responsivity and 1183% in detectivity at a light power of 1.2 mW/cm2. This work demonstrates the potential application of 2D van der Waals field-effect transistors with asymmetric Schottky contacts for broadband, high-performance, and tunable photodetection.