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Modern technology allows us to mimic biological functions with artificial devices. The human brain, including numerous neural cells that connect via synapses, enables us to handle complex tasks with ultra-low power consumption, which is one of the most important biological components that eager to emulate. Here, we propose and build a simple indium selenide (InSe)-based photonic synaptic device with unique gate tunable behaviours such as time-varying output current, auto-depression rate, and paired-pulse facilitation (PPF). A new inverse PPF behaviour is observed, characterized by the positive correlations to the time interval, which is opposite of those negative ones in previous studies. To unveil the origin of this new finding, both the substrate-dependent persistent photocurrent examination and low-frequency noise (LFN) measurements are performed to investigate the electric-controlled charge trapping/detrapping processes between the InSe and SiO2 interface. Furthermore, we systematically demonstrate such the specific evolution of the flexible plasticity within a low-operation voltage and a wide range of visible spectra. Interestingly, the inverse PPF can be employed to emulate more detailed characteristics of a biological brain such as the age-related changes of synaptic plasticity in real human brains. Thus, we believed that our findings provide a proof-of-concept for systematically mimicking the brain plasticity and advancing the development of energy-efficient artificial brains.

Multifunctional devices are expected to allow development of low-cost, highly integrated, and energy-efficient electronics for the internet of things (IoT) era. Here, we demonstrate an all-two-dimensional ReSe2/h-BN/graphene heterostructure (ReSe2 HS) consisting of a vertically coupled ReSe2 field-effect transistor and charge storage component, which possesses multifunctional characteristics for use in electronics and optoelectronics. As an electrically controlled non-volatile memory (NVM), the ReSe2 HS delivers high-performance multilevel data storage with a readout on/off current ratio exceeding 105 and excellent durability (>104 s) at an ultralow Vds of 50 mV, which benefits to the development of power saving devices. The ReSe2 HS design and high-photoresponsivity ReSe2 channel also achieve an energy efficient optical NVM with full-visible-spectrum distinction. Besides, the ReSe2 HS displays unique ambipolarity to operate as either an inverter or frequency doubler. We further propose a power-free ReSe2 HS optical memory matrix to simplify imaging systems. The ReSe2 HS shows promise for use in light-programmable information storage systems and neuromorphic computation with low power consumption.