A Visible-Blind Photodetector and Artificial Optoelectronic Synapse Using Liquid-Metal Exfoliated ZnO Nanosheets

Atomically thin 2D materials are highly sought for high-performance electronic and optoelectronic devices. Despite being a widely recognized functional material for a plethora of applications, ultra-thin nanosheets of zinc oxide (ZnO) at a millimeter-scale for developing high-performance electronic/optoelectronic devices have not been reported. This has prevented the exploration of electronic and optical properties of ZnO when it is only a few atoms thick. Here, a liquid metal exfoliation technique is used that takes advantage of the van der Waals forces between the interfacial oxide and the chosen substrate to obtain ZnO nanosheets with lateral dimensions in the millimeter scale and thickness down to 5 nm. Their suitability for applications is shown by demonstrating a visible-blind photodetector with high figures of merit as compared to other ZnO morphologies. At extremely low operating bias of 50 mV and low optical intensity of 0.5 mW cm−2, the ZnO photodetector demonstrates an external quantum efficiency (EQE), responsivity (R), and detectivity (D*) of 4.3 × 103%, 12.64 A W−1, and 5.81 × 1015 Jones at a wavelength of 365 nm. The trap-mediated photoresponse in the ZnO nanosheets is further utilized to demonstrate optoelectronic synapses. Versatile synaptic functions of the nervous systems are optically emulated with the ultra-thin ZnO nanosheets.