Visible-Active Artificial Synapses Based on Ultrathin Indium Oxide

One of the key requirements to emulate synaptic features in optoelectronic devices is the presence of persistent photoconductivity (PPC). While there are several visible-active materials, transparent semiconducting oxides (TSOs) have commercially established production processes and applications. Despite the inherently exceptional optoelectronic properties in many atomically thin TSOs along with PPC, their wide band gap renders them feasible only for ultraviolet (UV)-active synaptic applications. Hence, approaches need to be developed that allow one to tailor such semiconductors for visible-active optoelectronic synapses that are a strong emerging area of research. Over the past few years, liquid metal (LM) printing techniques have enabled the realization of many nonstratified oxides in an atomically thin form, resulting in oxide systems with enhanced optoelectronic performances, which can be further engineered using postsynthesis processing techniques. Here, we utilize a nonlayered ultrathin oxide, indium oxide (In 2 O 3 ), engineered to demonstrate a photoelectrical response in the visible spectrum with a peak responsivity of 6.67 × 10 3 A/W at 455 nm. The 2.2 nm thin sheets operating under a driving voltage of 200 mV are successfully able to detect short pulses under 500 ms while showcasing PPC characteristics without additional bias. Key synaptic and multisynaptic functionalities are replicated using blue and green light sources, demonstrating a viable pathway to integrate atomically thin oxide semiconductors for visible light-active optoelectronic synaptic applications.