Robust Self-powered Optoelectronic Synapses Based on Epitaxial InSe/GaN Heterojunction with Interfacial Charge-Trapping Layer

Neuromorphic devices that parallelize perception, preprocessing, and computation functions are expected to play a significant role in future non-von Neumann architecture computers. Herein, a new retina-inspired broadband self-powered optoelectronic synaptic device based on 2D/3D heterojunction of epitaxial InSe on GaN(0001) is reported. Few-layer n-type InSe is grown on p-type GaN by physical vapor deposition in an ultra-high vacuum (UHV) environment. The devices are fabricated using a shadow mask assisted UHV electrode deposition technique. High-resolution transmission electron microscopy images reveal that an atomically thin amorphous layer, which induces highly efficient charge trapping, is formed at the InSe/GaN interface. The photoresponse spans from visible to near-infrared, and the response time is prolonged to 10³ ms owing to the deep trapping levels. Thus, synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation with a high index of up to 170%, short-term plasticity, and high-pass filtering characteristics, are realized. Additionally, the synapses demonstrated the merit of realizing image sharpening and arithmetic operations on the same device under infrared and visible light illumination. This study provides a new platform of 2D/3D heterostructures for robust optoelectronic synapses that may find applications in post-Moore era neuromorphic vision systems.