Enhanced Electrical and Optoelectronic Characteristics of Few-Layer Type-II SnSe/MoS van der Waals Heterojunctions.

van der Waals heterojunctions formed by stacking various two-dimensional (2D) materials have a series of attractive physical properties, thus offering an ideal platform for versatile electronic and optoelectronic applications. Here, we report few-layer SnSe/MoS van der Waals heterojunctions and study their electrical and optoelectronic characteristics. The new heterojunctions present excellent electrical transport characteristics with a distinct rectification effect and a high current on/off ratio (∼1 × 10). Such type-II heterostructures also generate a self-powered photocurrent with a fast response time (<10 ms) and exhibit high photoresponsivity of 100 A W, together with high external quantum efficiency of 23.3 × 10% under illumination by 532 nm light. Photoswitching characteristics of the heterojunctions can be modulated by bias voltage, light wavelength, and power density. The designed novel type-II van der Waals heterojunctions are formed from a combination of a transition-metal dichalcogenide and a group IV-VI layered 2D material, thereby expanding the library of ultrathin flexible 2D semiconducting devices.