ZnO-WS2 heterostructures for enhanced ultra-violet photodetectors

Two-dimensional (2D) materials have attracted wide attention due to their exotic properties. In particular, the lack of dangling bonds makes it possible to build highly lattice mismatched heterostructures composed of 2D materials and conventional semiconductors. Here, we report that by simply stacking a chemical vapor deposition grown monolayer WS2 film onto the surface of a room temperature sputtered ZnO film, significant enhanced ultra-violet (UV) photoresponse can be achieved. In this heterostructure of ZnO-WS2, the ZnO film acts as a light harvesting layer while the WS2 monolayer functions as a carrier transport layer which facilitates the photocarrier transport and reduces its recombination. Such a mechanism was confirmed by the observation of further photoresponsivity improvement of the ZnO-WS2 heterostructure under vacuum which removes the surface absorbates and thereby increases the carrier mobility of WS2. The strategy presented here can be applied to other wide band-gap semiconductors, shedding light on high sensitivity and flexible UV photodetectors based on van der Waals heterostructures.