Giant Photoresponse Enhancement in Mixed-Dimensional Van der Waals Heterostructure through Dielectric Engineering

The reduced dielectric screening in the out of plane direction, makes 2D materials sensitive to the surrounding environment, offering a unique platform with greatly tunable optoelectronic properties. Large exciton binding energy in 2D materials limits their photogeneration efficiency. The strong electric field generated at a p-n junction will help in separating these strongly bound electron hole pairs. Here, the present study demonstrates how engineering the surrounding dielectric environment would facilitate a mixed dimensional van der Waals p-n junction to improve the photoresponse to a great extent. A 3D silicon-2D monolayer MoS2 heterostructure is fabricated as a model system. Nearly three orders of magnitude enhancement in photoresponse is observed by modulating the surrounding dielectric environment. This huge enhancement is attributed to the easy separation of photogenerated carriers due to the screening of Coulomb interaction. The dielectric also screens the impurity potential, reducing the charge carrier scattering. In addition, there is a change in the overall bandgap of the heterostructure producing a lower energy barrier for the charge carriers. The findings lay a general pathway for improving the efficiency of 2D material based photodetectors through dielectric engineering.