Van der Waals Heterostructures with Tunable Tunneling Behavior Enabled by MoO3 Surface Functionalization

Heterostructures of 2D materials represent a powerful material platform that has essentially defined the technological foundation for all modern electronic and optoelectronic devices. Although most of the reported heterostructures devices exhibit extraordinary electronic and optoelectronic properties, they depend on the proper combination of selected materials, which limits the broad tunability of the devices. Herein, it is demonstrated that a vertical van der Waals heterostructures (vdWHs) device, which is composed of MoS2 and MoTe2, can function as a backward tunneling diode, photovoltaic cell, and photodetector through surface functionalization of MoO3. The realization of this backward tunneling diode is attributed to the band alignment variation from type II to type III via in situ MoO3 functionalization. Furthermore, the power conversion efficiency of this vdWHs based photovoltaic device is significantly enhanced by nearly four times, benefiting from the more efficient photocarrier separation after MoO3 decoration. The enhanced photovoltaic effect can be retained even after air exposure, revealing the excellent air stability. Meanwhile, the modified vdWHs device exhibits the photodetecting property with photocurrent responsivity of around 2 A W-1 and external quantum efficiency about 400%. This work promises surface functionalization as an effective approach to broaden the device functionality of 2D heterostructures in electronics and optoelectronics.