Sn δ-Doped α-Ga2O3-Based MSM Photodetectors and Their Applications to Optoelectronic Artificial Synapse

Metal-semiconductor–metal (MSM) photodetectors (PDs) based on Sn $\delta $ -doped $\alpha $ -Ga2O3 with $\delta $ -doping durations of 40, 60, and 80 s were fabricated and studied. Longer $\delta $ -doping duration enhanced responsivity, external quantum efficiency, and specific detectivity but increased dark current and slowed decay time. The MSM PD with an 80-s $\delta $ -doping duration achieved a responsivity of 145.23 A/W, an external quantum efficiency of 78 297%, and a specific detectivity of $2.32\times 1011$ Jones. Beyond deep-UV sensing, these PDs demonstrated optoelectronic artificial synaptic behavior. The 80-s device exhibited 194% paired-pulse facilitation (PPF), 1377% spike-number-dependent plasticity (SNDP) with 64 pulses, and 344% spike-rate-dependent plasticity (SRDP) induced by five successive 10-Hz light pulses. In addition, SNDP and SRDP enabled the transition from short-term plasticity to long-term plasticity, a behavior absent in undoped $\alpha $ -Ga2O3. These findings demonstrate the potential of Sn $\delta $ -doped $\alpha $ -Ga2O3 MSM PDs for artificial neural networks and multifunctional optoelectronic applications.