Van der Waals heterostructures built from two-dimensional materials on a conventional semiconductor offer novel electronic and optoelectronic properties for next-generation information devices. Here we report that by simply stacking a vapor-phase-synthesized multilayer n-type WS2 film onto a p-type Si substrate, a high-responsivity Zener photodiode can be achieved. We find that above a small reverse threshold voltage of 0.5 V, the fabricated heterojunction exhibits Zener tunneling behavior which was confirmed by its negative temperature coefficient of the breakdown voltage. The WS2/Si heterojunction working in the Zener breakdown regime shows a stable and linear photoresponse, a broadband photoresponse ranging from 340 to 1100 nm with a maximum photoresponsivity of 5.7 A/W at 660 nm and a fast response speed of 670 μs. Such high performance can be attributed to the ultrathin depletion layer involved in the WS2/Si p-n junction, on which a strong electric field can be created even with a small reverse voltage and thereby enabling an efficient separation of the photogenerated electron-hole pairs.

A WS2–graphene epitaxial heterostructure based photodetector showed a high responsivity and a broad response spectrum.

As a typical two-dimensional (2D) semiconducting material, layered transition metal dichalcogenides (TMDCs) show promise in electronics and optoelectronics. To fully realize their potential, cost-effective large-area and layer-number modulated synthesis is highly desired. Here, taking MoS2 as an example, we demonstrate a layer-by-layer scalable growth of coalesced TMDC films on a moving sapphire substrate by local-feeding atmospheric-pressure chemical vapor deposition. By linear moving of the substrate across the cone-shaped diffusion concentration gradient of Mo-containing species and controlling the moving cycles, continuous MoS2 films with the thickness from a monolayer up to ~30 layers can be obtained. Compared with the growth on a stationary substrate, the monolayer film grown on a moving substrate shows preferable 2D epitaxial growth with much smoother surface morphology. We believe this can be attributed to the spatial separation of the initial nucleation step and the following 2D ripening process during substrate moving, which is the key to promoting the 2D lateral growth. The results shed light on developing new synthetic strategies toward atomic-thickness-controlled growth of 2D TMDC films in a scalable and efficient process that is suitable for large-area device fabrication.