Light-Triggered Ternary Device and Inverter Based on Heterojunction of van der Waals Materials

Multivalued logic (MVL) devices/circuits have received considerable attention because the binary logic used in current Si complementary metal-oxide-semiconductor (CMOS) technology cannot handle the predicted information throughputs and energy demands of the future. To realize MVL, the conventional transistor platform needs to be redesigned to have two or more distinctive threshold voltages (V_THs). Here, we report a finding: the photoinduced drain current in graphene/WSe₂ heterojunction transistors unusually decreases with increasing gate voltage under illumination, which we refer to as the light-induced negative differential transconductance (L-NDT) phenomenon. We also prove that such L-NDT phenomenon in specific bias ranges originates from a variable potential barrier at a graphene/WSe₂ junction due to a gate-controllable graphene electrode. This finding allows us to conceive graphene/WSe₂-based MVL logic circuits by using the I_D-V_G characteristics with two distinctive V_THs. Based on this finding, we further demonstrate a light-triggered ternary inverter circuit with three stable logical states (ΔV_out of each state <0.05 V). Our study offers the pathway to substantialize MVL systems.