Infrared Photodetector Based on van der Waals MoS2/MoTe2 Hetero-Bilayer Modulated by Photogating

Abstract

Photodetectors based on 2D hetero-bilayers can overcome the bandgap limitations of individual 2D monolayers and operate at relatively long wavelengths. However, ultra-low light absorptions within hetero-bilayers result in extremely weak photoresponsivity. Here, an infrared photodetector based on the MoS₂/MoTe₂ type-II hetero-bilayer is demonstrated to reach a photoresponsivity of 0.55 A W⁻¹ at 1550 nm, well beyond energy band cut-offs of monolayer MoS₂ and MoTe₂, primarily resulted from the photogating effect. Raman and photoluminescence (PL) spectroscopy reveal strong interlayer couplings in the hetero-bilayer, and a broad PL peak around 1550 nm is observed that is ascribed to interlayer transitions of carriers. The photodetector showcases a broadband detection capability from 1100 to 1700 nm, with a peak at 1550 nm corresponding to the interlayer absorption. Electrical characterization of the hetero-bilayer-based field-effect transistor and kelvin probe force microscopy reveal efficient interlayer hole transfer. The highly responsive MoS₂/MoTe₂ infrared photodetector offers a large photo-gain of ≈10³ and a time constant of 130 ms. The research illuminates how interlayer transitions affect 2D hetero-bilayer-based photodetectors and advances the utilization of layered semiconductor heterostructures.