posted on 2023-11-21, 00:04authored byZheng Wen, Shuhan Wang, Fangzhou Yi, Dingting Zheng, Chengyuan Yan, Zhenhua Sun
Fully
optical artificial synapses are crucial hardware for neuromorphic
computing, which is very promising to address the future large-scale
computing capacity problem. The key characteristic required in a semiconductor
device to emulate synaptic potentiation and depression in a fully
optical artificial synapse is the bidirectional photoresponse. This
work integrates wide-band-gap TiO2 polycrystals and narrow-band-gap
PbS quantum dots into a graphene transistor simultaneously, providing
the device with both near-ultraviolet and near-infrared photoresponses
through the photogating effect. Moreover, the TiO2 serves
as a hole-trapping matrix and the PbS as an electron-trapping matrix,
which impose opposite effects to the device after photoexcitation,
resulting in a photoresponse in the opposite polarity. As a result,
the device demonstrates a wavelength-dependent bidirectional photoresponse,
which enables it to be utilized as a fully optical artificial synapse.
By using near-ultraviolet or near-infrared lights as stimuli, the
device successfully mimics synaptic plasticity, including synaptic
potentiation/depression, paired-pulse facilitation, and spike-rating-dependent
plasticity, as well as the human brain-like transition of short-term
memory and long-term memory and learning-experience behavior. This
work validates the methodology of combining different trap matrices
to achieve the bidirectional photoresponse, which can significantly
inspire future research in fully optical artificial synapses.