Low-Temperature Deposition of Polycrystalline ε-Ga₂O₃ for Deep Ultraviolet Perceptual Photodetection

Metastable ε-Ga₂O₃ holds promise for integrated neuromorphic memory and photosensing owing to its spontaneous polarization and low-temperature deposition compatibility. However, realizing its optoelectronic perception function is hindered by poor control over crystalline allotropes and complex defect-mediated carrier trapping. Here, we address these issues by achieving low-temperature (350 °C) deposition of polycrystalline ε-Ga₂O₃ with tailored photocarrier dynamics using reactive oxygen plasma-enhanced atomic layer deposition. This low-temperature strategy suppresses undesired phase transformation and enables defect engineering. Microstructure analyses confirm (002)-oriented polycrystalline ε-Ga₂O₃ with a triple domain twinning architecture that yields macroscopic pseudohexagonal symmetry and reveal an orientation relationship of ε-Ga₂O₃(002)//α-Al₂O₃(006) on c-plane sapphire. The ε-Ga₂O₃ deep ultraviolet photodetectors exhibit a rapid recovery time of 0.03 s and a high detectivity of 8 × 10¹¹ Jones under a low bias of 1 V. At biases exceeding 10 V, persistent photoconductivity emerges, attributed to bias-addressed carrier trapping at oxygen vacancy defects of different energy depths. In neuromorphic mode, key synaptic behaviors─paired-pulse facilitation, excitatory postsynaptic current, and spike rate-dependent plasticity─are emulated, and high-accuracy image recognition is achieved. This work establishes a low-temperature growth strategy for ε-Ga₂O₃ that integrates photodetection and neuromorphic visual functionality in a single material system.