Photodiode-Like Behavior and Excellent Photoresponse of Vertical Si/Monolayer MoS(2) Heterostructures

Monolayer transition metal dichalcogenides (TMDs) and their van der Waals heterostructures have been experimentally and theoretically demonstrated as potential candidates for photovoltaic and optoelectronic devices due to the suitable bandgap and excellent light absorption. In this work, we report the observation of photodiode behavior in (both n- and p- type) silicon/monolayer MoS(2) vertical heterostructures. The photocurrent and photoresponsivity of heterostructures photodiodes were dependent both on the incident light wavelength and power density, and the highest photoresponsivity of 7.2 A/W was achieved in n-Si/monolayer MoS(2) vertical heterostructures photodiodes. Compared with n-Si/MoS(2) heterostructures, the photoresponsivity of p-Si/MoS(2) heterostructure was much lower. Kelvin probe microscope (KFM) results demonstrated the more efficient separation of photogenerated excitons in n-Si/MoS(2) than that in p-Si/MoS(2). Coupling KFM results with band alignments of (p-, n-) Si/MoS(2) heterostructures, the origins of photodiode-like phenomena of p-Si/MoS(2) and n-Si/MoS(2) have been unveiled, that is intrinsic built-in electric field in p-n junction, and modulated barrier height and width at the interface in n-n junction. Our work may benefit to the deep understanding of the integration of two-dimensional materials with more conventional three-dimensional semiconductors, and then contribute to the developments in the area of van der Waals heterostructures.