Heteroepitaxy of ε‐Ga₂O₃ thin film for artificial synaptic device

Abstract Emerging‐wide bandgap semiconductor Ga 2 O 3 shows distinct characteristics for optoelectronic applications and a stable crystal phase of Ga 2 O 3 is highly desired. Herein, we have first reported a metal‐semiconductor‐metal structure photonic synaptic device based on the ε ‐Ga 2 O 3 thin film. The ε ‐Ga 2 O 3 epilayer is grown on the c ‐sapphire with a low temperature nucleation layer, which presents a crystal orientation relationship with the c ‐sapphire ( ε ‐Ga 2 O 3 <010> // c ‐sapphire <1–100> and ε ‐Ga 2 O 3 <001> // c ‐sapphire <0001>). The ε ‐Ga 2 O 3 photonic device was stimulated by UV pulses at different pulse widths, pulse intervals, and reading voltages. Under the UV pulse excitation, the photonic device exhibits primary synaptic functions including excitatory postsynaptic current, short term memory, pair pulse facilitation, long term memory, and STM‐to‐LTM conversion. In addition, stronger and repeated stimuli can naturally contribute to the higher learning capability, thus prolonging the memory time.