P-type laser-doped WSe2/MoTe2 van der Waals heterostructure photodetector

Abstract

Van der Waals heterostructures (vdWHs) based on two-dimensional (2D) materials are being studied extensively for their prospective applications in photodetectors. As the pristine WSe2/MoTe2 heterostructure is a type I (straddling gap) structure, it cannot be used as a photovoltaic device theoretically, although both WSe2 and MoTe2 have excellent photoelectric properties. The Fermi level of p-doped WSe2 is close to its valence band. The p-doped WSe2/MoTe2 heterostructure can perform as a photovoltaic device because a built-in electric field appears at the interface between MoTe2 and p-doped WSe2. Here, a 633 nm laser was used for scanning the surface of WSe2 in order to obtain the p-doped WSe2. x-ray photoelectron spectroscopy (XPS) and electrical measurements verified that p-type doping in WSe2 is produced through laser treatment. The p-type doping in WSe2 includes substoichiometric WOx and nonstoichiometric WSex. A photovoltaic device using p-doped WSe2 and MoTe2 was successfully fabricated. The band structure, light-matter reactions, and carrier-transport in the p-doped WSe2/MoTe2 heterojunction were analyzed. The results showed that this photodetector has an on/off ratio of ≈104, dark current of ≈1 pA, and response time of 72 μs under the illumination of 633 nm laser at zero bias (Vds = 0 V). The proposed p-doping method may provide a new approach to improve the performance of nanoscale optoelectronic devices.