Defect-induced persistent photoconductivity and nonvolatility in two-dimensional BiSe thin film for neuromorphic vision sensing capability.

Optical synaptic devices (OSDs) have neuromorphic vision sensing capability showing great potential in breaking the von Neumann bottleneck and facilitating future artificial vision systems. However, the applications of two-dimensional (2D) material-based OSDs are still impeded by complicated structures, preparation techniques and so on. In this work, we propose a 2D OSD based on BiSe films prepared by a chemical vapor deposition method followed by an in-situ thermal treatment. We have found that the thermal treatment at 350 ℃ creates the most n-type defects in the film that can induce persistent photoconductivity (PPC) by trapping and de-trapping electrons. The device exhibits synaptic behaviors under illumination at 450 nm and 550 nm, including long-term potentiation (LTP), short-term potentiation (STP), the transition between them and pair-pulse-facilitation (PPF). For 550 nm light, the device has a long memory ability that the photocurrent after attenuation of 100 s (500 s) still has a memory level of 80 % (62 %), while a nonvolatility is observed. Our work sheds light on the design of 2D material-based OSDs with a simple structure by defects engineering, elaborates on the mechanisms of PPC and non-volatile caused by defect states, and facilitates the simplification of future artificial vision systems.