Bidirectional Photoresponse in a Mixed-Dimensional MoS2/Ge Heterostructure and Its Optic-Neural Synaptic Behavior for Colored Pattern Recognition

Realization of multi-functional synaptic devices is imperative to deploy high-performance brain-like vision systems. Here, a junction field-effect transistor based on a two-dimensional MoS2/three-dimensional Ge heterojunction structure is presented. The heterojunction gate ensures efficient electrostatic gate control and eliminates hysteresis, which highlights its capability for high-performance electronic circuit applications. With the visible absorptive MoS2 channel and the infrared absorptive Ge gate, a positive photoresponse to visible light and a negative photoresponse to infrared light are obtained simultaneously. Responsivities reach as high as 24.9 and −0.40 A/W at 532 and 1550 nm, corresponding to a detectivity of 7.9 × 1011 and −1.3 × 1010 Jones. Meanwhile, based on its optical stimulation-controlled synaptic behaviors, an optoelectronic neural network for colored digit pattern recognition is developed. The recognition accuracy reaches as high as 89.6 and 91.6% for visible and near-infrared patterns, respectively. These results demonstrate a new pathway for realizing novel multi-wavelength neuromorphic visual systems.