P-type laser-doped WSe/MoTe van der Waals heterostructure photodetector.

Van der Waals heterostructures (vdWHs) based on two-dimensional (2D) materials are being studied extensively for their prospective applications in photodetectors. As the pristine WSe/MoTe heterostructure is a type I (straddling gap) structure, it cannot be used as a photovoltaic device theoretically, although both WSe and MoTe have excellent photoelectric properties. The Fermi level of p-doped WSe is close to its valence band. The p-doped WSe/MoTe heterostructure can perform as a photovoltaic device because a built-in electric field appears at the interface between MoTe and p-doped WSe. Here, a 633 nm laser was used for scanning the surface of WSe in order to obtain the p-doped WSe. x-ray photoelectron spectroscopy (XPS) and electrical measurements verified that p-type doping in WSe is produced through laser treatment. The p-type doping in WSe includes substoichiometric WO and nonstoichiometric WSe. A photovoltaic device using p-doped WSe and MoTe was successfully fabricated. The band structure, light-matter reactions, and carrier-transport in the p-doped WSe/MoTe heterojunction were analyzed. The results showed that this photodetector has an on/off ratio of ≈10, dark current of ≈1 pA, and response time of 72 μs under the illumination of 633 nm laser at zero bias (V = 0 V). The proposed p-doping method may provide a new approach to improve the performance of nanoscale optoelectronic devices.