Bias-Tunable Dual-Mode Optoelectronic Device Based on a SiC/β-Ga2O3 Heterojunction for Photodetection and Optical Synapse

Abstract

Integrating ultraviolet photodetection and persistent optical memory in a single compact device is challenging because the two functions require contrasting carrier-recovery dynamics. Here, we demonstrate bias-only reconfiguration of a two-terminal SiC/β-Ga₂O₃ heterojunction between a photodetector-like mode and an optoelectronic-synapse mode. An approximately 27 nm Ga₂O₃ layer was deposited on n-type 4H-SiC by plasma-enhanced atomic layer deposition and crystallized into β-Ga₂O₃ by postdeposition annealing at 700 °C. At bias voltage V_D = 0.1 V under 254 nm illumination at 30 μW/cm², the device yields a responsivity (R) of 3.8 A/W, a photocurrent-to-dark-current ratio (PDCR) of 24, an external quantum efficiency (EQE) of 1.85 × 10³%, and a shot-noise-limited specific detectivity (D*) of 3.0 × 10¹² Jones. At the same irradiance, the responsivity ratio R₂₅₄/R₃₈₀ reaches 8.98, while the visible-light response remains at the experimental background level, corresponding to a conservative lower bound of R₂₅₄/R₅₀₀ > 100. At V_D ≥ 1.5 V, persistent photoconductivity dominates, enabling a paired-pulse-facilitation index of 156%, pulse-interval-controlled short-term-to-long-term memory conversion, and associative learning under dual-wavelength UV stimulation. Control-device, transient, structural, and spectroscopic results support a working model in which a weak type-II alignment facilitates bias-regulated interfacial electron transfer and defect-state recapture. These results establish a low-voltage, gate-free route toward compact, reconfigurable deep-UV sensors and neuromorphic vision devices.