Fig. 4: Multilevel logic operation and memory characteristics upon optoelectronic inputs.

Measured photoresponse during periodic illumination using (a) deep-Red and (b) Blue light and following alternating gate pulses. The photoresponse displays four distinct current levels marked by the four different color bands. c Schematic illustration of the logic circuit operation of the fabricated multibit memory device, where the gate and light pulses are supplied as input to achieve four distinct readout current levels. Schematic energy-band diagram illustration of photocarriers flow for different gate-bias voltages at (d) equilibrium (0 V_G), (e) +V_G, and (f) –V_G. The photocarriers flow and ferroelectric field in In₂Se₃, along with the built-in field directions, are marked by the blue-red, green and purple arrows, respectively. The band-bending and relative barrier heights are adapted from the surface potential profiles for two extreme cases.