RGB-Sensitive TeOx/InZnO Heterojunction Phototransistor for Visible-Light-Driven Optoelectronic Synapses

Abstract

Visible-light-responsive optoelectronic synapses are attracting increasing attention for neuromorphic vision systems because they integrate optical sensing and information processing within a single device. However, conventional oxide semiconductor phototransistors are generally limited by their wide bandgap, resulting in weak visible-light absorption and insufficient synaptic performance. Here, we demonstrate a thickness-optimized TeO_x/IZO heterojunction optoelectronic synaptic phototransistor that achieves efficient visible-light sensing and neuromorphic functionality through enhanced photocarrier generation and defect-assisted carrier trapping. Systematic optimization of the TeO_x layer reveals that a thickness of 5 nm provides the optimum balance between visible-light absorption, electrical switching characteristics, and carrier transport. The optimized device exhibits a low dark current of approximately 1 × 10⁻¹² A, a high on/off current ratio of ∼10⁸, and wavelength-dependent photoresponse enhancements of up to 2377.6% under green-light illumination compared with pristine IZO devices. Furthermore, the device successfully emulates essential synaptic functions, including excitatory postsynaptic current, short- and long-term memory, paired-pulse facilitation, and long-term potentiation/depression, while achieving a handwritten digit recognition accuracy of ∼88%. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and photo-induced current transient spectroscopy reveal that the superior photosynaptic performance originates from an optimal balance among visible-light absorption, interfacial carrier transfer, and shallow-defect-assisted carrier trapping. These results establish the TeO_x/IZO heterojunction as an effective platform for oxide-based visible-light neuromorphic vision systems.