Large-area MoS₂-MoO_x heterojunction thin-film photodetectors with wide spectral range and enhanced photoresponse

We report the enhanced photoresponse in MoS₂-MoO_x heterojunction thin film structures on SiO₂/Si substrates to demonstrate the feasibility of using them as highly responsive photodetectors with a wide spectral range from visible to near-ultraviolet light. Vertically stacked MoS₂-MoO_x heterojunction structures were obtained through two-step chemical vapor deposition composed of MoO_x thin film deposition and subsequent sulfurization of the topmost region of as-deposited MoO_x into MoS₂. The formation of heterojunction structures was revealed by transmission electron microscopy and x-ray photoelectron spectroscopy analysis. Under an incident light of 405 nm and 638 nm in wavelength, our MoS₂-MoO_x heterojunction thin film structures exhibited significantly higher absorbance, photoresponsivity, and specific detectivity than MoO_x thin films. Moreover, a highly uniform photoresponse was obtained throughout heterojunction thin film structures. These results demonstrate that MoS₂-MoO_x heterojunction thin film structures can be a potentially promising material system scalable into large-area photodiode arrays to build active-matrix high-energy-selective photodetectors.