Self-organized metasurface enabling negative photoconductance and memristive behavior via van der Waals interaction

Negative photoconductance (NPC) and memristive behavior have been observed simultaneously in planar, metal-oxide-based heterojunctions. Self-organized TiO2 crystalline metasurface thin films were prepared by spin coating with polymer-templated precursors, yielding a smooth, uniform, and full-coverage surface with metastructure features sizing from 1 to 3 μm. After depositing CuO crystalline thin films on a conductive substrate, two metal-oxide thin films are held together face-to-face by mechanical clips to form a heterojunction diode. Due to stacking architecture, van der Waals interactions play a crucial role at the interface. The IV characteristics of the pn heterojunctions exhibit pronounced rectification and NPC, with the current dropping by a factor of 6 as the temperature increases by 20 °C under white-light irradiation. The NPC can be attributed to increased charge-carrier recombination and lattice vibrations induced by infrared light absorption, leading to a temperature rise. The cyclic IV curves exhibit a narrow hysteresis, a characteristic of a memory-type resistor during voltage sweeping. The mechanism underlying memristive traits has been qualitatively hypothesized using a circuit model based on series and parallel connections of resistors and capacitors, reflecting the metastructure at the interface. The fabricated memdiodes may serve as alternative electronic elements for integration into photo-memory-type computing hardware.