# All-Optical Artificial Synapse Based on ε-Ga2O3 and β-Ga2O3 Mixed-Phase Thin Films

## TL;DR

Researchers developed an all-optical artificial synapse using gallium oxide films that mimic biological synaptic functions like memory and learning.

## Contribution

The study introduces a novel all-optical memristor using ε/β-Ga2O3 mixed-phase films to simulate synaptic plasticity with light.

## Key findings

- ε/β-Ga2O3 mixed-phase films show persistent resistance retention exceeding 104 seconds.
- Optical pulse parameters can model short-term and long-term synaptic plasticity.
- The device exhibits air stability with photoconductivity maintained for over a year.

## Abstract

All-optical memristors possess light-sensing and storage capabilities while simultaneously simulating human synaptic functions, demonstrating immense potential in the field of brain-inspired computing for realizing bionic synapses and brain-like intelligence. In this work, we successfully produced ε-Ga2O3 films, ε/β-Ga2O3 mixed-phase films, and β-Ga2O3 films via chemical vapor deposition (CVD). The optical output and optical response characteristics of the thin films are investigated under 254 nm and 365 nm lasers. The CVD-grown ε-Ga2O3 is found to process a small amount of defects and insignificant memristive properties and the β-Ga2O3 obtained from the annealing of ε-Ga2O3 exhibits superior crystal quality but lacks memristive properties, while the ε/β-Ga2O3 mixed-phase films grown directly by CVD contain a fair amount of defects and demonstrate persistent resistance retention exceeding 104 s. Based on the excellent memristive properties of ε/β-Ga2O3 mixed-phase films, we conducted experiments simulating optical synapses. By adjusting optical pulse parameters (intensity, repetition rate, and duration), we successfully modeled the short-term plasticity (STP) and long-term plasticity (LTP) observed in biological synapses. Experiments confirm that light stimulation can effectively induce synaptic behaviors, such as the progressive conversion of short-term memory (STM) into long-term memory (LTM), and further fully reproduce the neuroplasticity process of “learning-forgetting-relearning.” This study demonstrates a photoconductive synapse memristor based on the wide-bandgap material gallium oxide, exhibiting exceptional air stability with sustained photoconductivity maintained for over a year. This study provides new insights into the practical application feasibility of all-optical artificial synapses based on gallium oxide.