Mixed-Dimensional Van der Waals Heterostructures Enabled Optoelectronic Synaptic Devices for Neuromorphic Applications

Neuromorphic devices provide a hardware platform to implement synaptic functions into artificial electronic devices, which opens a new way to overcome the von Neumann bottleneck from the device level. Optoelectronic synaptic devices are expected to break the limitations of electrically stimulated synapses due to wider bandwidth, higher speed, and lower crosstalk. However, most optoelectronic synaptic devices are enabled by the defect-dominant photo-generated carrier trapping/de-trapping. Therefore, designable device structure and controllable synaptic functions are urgently desirable in optoelectronic synaptic devices. Among various functional materials, low-dimensional materials exhibit excellent optical and electrical properties and can be easily applied to build van der Waals (vdW) heterostructures with ideal surface characteristics. Herein, the basic morphology and characteristics of low-dimensional materials have been introduced and the typical constitution of mixed-dimensional (MD) vdW heterostructures has been reviewed to highlight their unique light-matter interaction. Then, optoelectronic synaptic devices are classified into three categories by the role of light as input, modulated and output signals based on different photoelectric conversion mechanisms. Furthermore, a bridge between neuromorphic devices and practical applications is established to illustrate their potential in neuromorphic systems. Finally, great challenges and possible study directions are presented to guide the development of MD vdW heterostructures in future neuromorphic systems.