PLD-Grown Semi-Insulating Ga2O3 Thin Film-Based Optoelectronic Artificial Synaptic Devices for Neuromorphic Computing Applications

Development of artificial opto-electronic synaptic devices plays a crucial role for the practical implementation of energy-efficient, parallel processing of human brain. In this article, two terminal inter-digitated devices are fabricated on Gallium oxide (Ga₂O₃) thin films grown on sapphire substrates by pulsed laser deposition (PLD) technique to study its ability to mimic biological synaptic behaviors. The layers are found to exhibit long persistent photo-conductivity (PPC) effect, which is identified to be the key parameter to replicate the behavior of biological synapses. Channel resistance and PPC time constants should also be optimized to improve the efficiency of response and energy consumption of synaptic devices. It has been observed that both conductivity and the PPC decay time of Ga₂O₃-films can be controlled by varying oxygen pressure $\left({\varnothing }_{O_2}\right)$ and growth temperature (T_G). These devices demonstrate their ability to perform paired pulse facilitation (PPF) at very low applied bias in mV-range. They can mimic biological synapses showing short-to-long-term memory transition (STM-to-LTM) and learning-forgetting behavior. One of these devices is found to show synaptic behavior with the energy consumption of as low as 71fJ electrical and 21nJ optical per synaptic event. These findings thus strengthen the candidature of Ga₂O₃ films for the development of next-generation opto-electronic neuromorphic devices and systems.