An optically controlled synaptic device based on a PdSe₂/α-In₂Se₃ vdW heterostructure FET

Visual synaptic devices show great promise for advanced neuromorphic hardware, offering a viable solution to the von Neumann bottleneck. However, achieving bidirectional optical control remains a considerable challenge. Herein, we demonstrate an all 2D heterostructure FET consisting of few-layer PdSe₂ and α-In₂Se₃, designed as an optically controlled synaptic device with ferroelectric assisted tunability. The device emulates multiple forms of spike-dependent plasticity, exhibiting excitatory and inhibitory synaptic responses in the 642-980 nm and 406-520 nm spectral range, respectively. Moreover, the optically induced excitatory and inhibitory synapses can be modulated by an electrical gate pulse, utilizing the spontaneous polarization of α-In₂Se₃. By leveraging the coupled ferroelectric and optical properties of In₂Se₃, the device exhibits an extended retention time of post-synaptic current (PSC) and enhanced device performance in terms of responsivity (R) and detectivity (D) compared with its PdSe₂-based counterparts. Logic gate operations (OR and AND) were demonstrated using 642 nm, 785 nm and 406 nm wavelengths as optical inputs. In addition, a three-layer artificial neural network (ANN) was trained to recognize a 28 × 28 pixel handwritten MNIST dataset by a backpropagation algorithm demonstrating high recognition accuracy of 96% and 97% under wavelengths of 642 nm and 406 nm, respectively. This study provides an effective strategy for the development of versatile optically controlled neuromorphic devices as fundamental building blocks for on-chip optical communication, optoelectronic logic, and Internet of Things (IoT) applications.