An artificial optoelectronic synapse based on an InAs nanowire phototransistor with negative photoresponse

In this paper, an artificial nanoscale optoelectronic synapse is designed and simulated. The device is based on an InAs nanowire phototransistor covered with a native oxide layer, which captures the photo-generated hot electrons before the thermalization back to the conduction band. Due to the large surface-to-volume ratio and high electron mobility of InAs nanowire, the device exhibits a high responsivity of 10(4) A/W under 633 nm excitation at 300 K. At low illumination power density range of 10(-5) similar to 3 W/cm(2), the device shows synaptic behaviors including short-term potentiation, long-term potentiation and paired-pulse facilitation. The influence of different factors, including illumination intensity, gate voltage and the depth and concentration of traps on the synaptic behaviors, is studied in detail. By adjusting the gate voltage, a transition from short-term potentiation to long term potentiation is realized. The synaptic behaviors are explained by energy band diagram and distribution of current density and trapped charges. This work may pave the way for the development of low-consumption high-speed large-bandwidth synaptic devices.