Negative photoconductivity (NPC), a reduction in photoconductivity under light illumination, could provide low power consumption and high-speed frequency response. The NPC has been generally observed in low-dimensional materials, which can be easily affected by the trapping of photocarriers. However, a gradual transition between NPC and positive photoconductivity (PPC) by controlling the light intensity has not been reported. In this study, a gradual and reversible switching between NPC and PPC is achieved in a van der Waals heterostructure of graphene and MoTe2. The initially observed NPC state becomes a PPC state with the increase in light intensity. The switching between NPC and PPC is considered to originate from the hole trapping in MoTe2. The hole trapping can induce a shift in the Fermi level of MoTe2 and thus change the junction characteristics between the graphene and MoTe2, which determine the photoresponse type (NPC or PPC). Notably, the switching from one state to the other can also be reversed, depending on the gate bias. The stable and reversible effect upon light illumination and application of a gate voltage could be used in optoelectronic devices and optical communications.
Keywords: MoTe2; negative photoconductivity; photodevice; trap-assisted photogating effect; vdW heterostructure.