Ultra-highly linear Ga2O3-based cascade heterojunctions optoelectronic synapse with thousands of conductance states for neuromorphic visual system
Peng Li, Xuanyu Shan, Ya Lin, Yi Du, Jiangang Ma, Zhongqiang Wang, Xiaoning Zhao, Ye Tao, Haiyang Xu, Yichun Liu
Abstract
Abstract Ultrawide bandgap semiconductor optoelectronic synapses can perform high-parallel computing with a low false alarm rate, making them ideal for building deep-ultraviolet (DUV) neuromorphic visual system (NVS). However, the rapid carrier recombination in these optoelectronic synapses results in a poor number of conductance states and a low linear weight update protocol, consequently degrading the image recognition accuracy of DUV NVSs. This work proposes a type of cascade heterojunctions capable of finely tuning the dynamics of photogenerated carriers, utilizing aluminum interdigital electrodes sandwiched between tin-doped Ga 2 O 3 and oxygen-deficient hafnium oxide (GTO/Al/HfO x ) films. The built-in fields at the GTO/HfO x heterojunction and the Al/HfO x hole Schottky junction interfaces facilitate the separation of photogenerated carriers and the subsequent trapping of holes by the oxygen defects in the HfO x , respectively. The GTO/Al/HfO x optoelectronic synapses exhibit an ultrahigh responsivity of over 10 4 A/W and a large photo-to-dark current ratio of 6 × 10 5 , which results in exceptional synaptic plasticity with unprecedented 4096 conductance states and excellent linearity with a fitting coefficient of 0.992. These attributes enable the GTO/Al/HfO x optoelectronic synapses to execute logical operations with fault-tolerance capability and to achieve high-accuracy fingerprint classification. The innovative cascade heterojunctions design, along with the elucidated carrier dynamics modulation mechanism, facilitates the development of DUV NVSs.