LAUSR

Layered two-dimensional van der Waals (vdW) semiconductors and their heterostructures have been shown to exhibit positive photoconductance (PPC) in many studies. A few recent reports have demonstrated negative photoconductance (NPC) as well that can enable broadband photodetection besides multi-level optoelectronic logic and memory. Controllable and reversible switching between PPC and NPC is a key requirement for these applications. This report demonstrates visible-to-near infrared wavelength-driven NPC and PPC, along with reversible switching between the two, in an air stable, high mobility, broadband black phosphorus (BP) field effect transistor (FET) covered with a few layer MoS2 flake. The crossover switching wavelength can be tuned by varying the MoS2 bandgap through its flake thickness and the NPC and PPC photoresponsivities can be modulated using electrostatic gating as well as laser power. Recombination-driven NPC and PPC allows for reversible switching at reasonable time scales of a few seconds. Further, gate voltage-dependent negative persistent photoconductance enables synaptic behavior that is well-suited for optosynaptic applications.