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

Abstract

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.

Bidirectional Invisible Photoresponse Implemented in a Traps Matrix-Combination toward Fully Optical Artificial Synapses

“…Then, 20 light pulses of 905 nm with an intensity of 130.82 mW/cm 2 and a duration of 5 s were applied to the device at a frequency of 0.04 Hz, which managed to depress the ΔPSC to about zero. The nonlinearity of the potentiation and depression curves are calculated to be about 1.31 and 0.28, respectively . The 360–905 nm working cycle is repeated 50 times, as shown in Figure S3a.…”

“…Optoelectronic semiconductor devices featuring wavelength-dependent bidirectional photoresponse have been demonstrated applicable as the fully optical artificial synapses. − In this way, the electrical conductance of the devices is deemed as the synapse weight, and the synapse plasticity, including the potentiation and depression, is embodied as the positive and negative photoresponse, respectively. Realizing the wavelength-dependent bidirectional photoresponse and the synapse plasticity simultaneously in a single device poses a strict requirement for light-sensitive materials.…”

“…Realizing the wavelength-dependent bidirectional photoresponse and the synapse plasticity simultaneously in a single device poses a strict requirement for light-sensitive materials. Such a requirement has been barely reported met by a single material except for the black phosphorus in ambient, which might be bothered by the low stability of the black phosphorus in air. − On the other hand, the combination of distinct light-sensitive materials like CH 3 NH 3 PbBr 3 /ZnO, PbS/ZnO, O 2 -deficient IGZO/O 2 -rich IGZO, Bi 2 O 2 Se/graphene, MoS 2 /Ge, and pyrenyl graphdiyne/PbS quantum dots can address the requirement better, producing well-performing fully optical synaptic devices. In this respect, the combination of the oxide and the colloidal quantum dot semiconductors is worth an in-depth study due to their excellent optoelectronic properties and abundant trap-states. , For example, in 2019, Li et al reported a two-terminal memristor based on the ZnO/PbS hybrid heterostructure that can emulate the synaptic activities in the fully photon modulated mode, manifesting the great application potential of the oxide/quantum dots semiconductors combination .…”

Recent Progress of Polymeric Dielectrics in Molybdenum Disulfide-Based Devices

“…Thus, it is urgent to find a new class of materials to overcome these technical problems. With the nature of ultrathin thickness, dangling-free bonds and tunable band structure, transition metal dichalcogenides (TMDCs) have shown excellent electrical properties, unique optoelectronic properties, and mechanical flexibility that could be transferred to arbitrary substrates, which are becoming one of the most promising materials to replace traditional silicon-based materials. − Thereinto, molybdenum disulfide (MoS 2 ) with a typical layered structure is widely studied. − According to current progress, MoS 2 possesses the thickness-dependent energy band to widen its absorption spectrum and the large surface-to-volume ratio to assist charge trapping, which lay a good foundation for the development of optoelectronic devices for sensors, − displays, − recognition, − and other diversified applications. − Furthermore, air-stabilized MoS 2 could overcome the phonon scattering through the interface engineering to obtain ultrahigh electrical properties at room temperature and achieve the large-size growth by the regulation of preparation process, which provide advantages for the development of large-scale miniaturized integrated circuits. , Markedly, MoS 2 -based flexible integrated logic circuits as the optimization of the growth process have been successfully studied, which obtained good device yield and excellent electrical performance with the mobility of 55 cm 2 V –1 s –1 , high on/off ratios of 10 10 , and current densities of 35 μA μm –1 …”

All-Fiber Synapse Utilizing Phase Change Materials for Information Recognition and Processing

“…While the amplifiers − and lasers , based on photonic devices can be used to implement STDP for supervised or unsupervised learning with picosecond scale speed, they require constant electrical energy to maintain the states. Photonic synapses based on field-effect transistors exhibit impressive optical perception and memory properties in simulating human vision. − However, these synapses require additional optical circuit costs, and their calculation efficiency is limited by the response time in milliseconds due to carriers’ capture and release. Furthermore, Gholipour et al develop nonvolatile photonic synapses based on amorphous gallium lanthanum oxysulfide microfibers, but they utilize additional spatial light for stimulation and do not work at the telecoms band .…”