Visible-Light-Stimulated\nOptoelectronic Neuromorphic\nTransistor Based on Indium–Gallium–Zinc Oxide via Bi<sub>2</sub>Te<sub>3</sub> Light Absorption Layer

To emulate a visual perception system, a bismuth telluride\n(Bi<sub>2</sub>Te<sub>3</sub>)/indium–gallium–zinc oxide\n(IGZO)\nheterostructure is introduced for optoelectronic neuromorphic transistors\n(ONTs). Amorphous IGZO is applied as a channel layer to exhibit low\noff-current, high mobility, and persistent photoconductivity, enabling\nlight-stimulated neuromorphic characteristics. The atomic ratio of\nIn/Ga/Zn was 9.4:9.8:5.2. For a light absorption layer, Bi<sub>2</sub>Te<sub>3</sub> is applied due to a small bandgap, high photoresponse,\nand carrier concentration. However, conventional optoelectronic devices\nusing Bi<sub>2</sub>Te<sub>3</sub> exhibit insufficient performance\nowing to their excessive conductivity. To resolve the constraint,\nthe oxidation of Bi<sub>2</sub>Te<sub>3</sub> is performed to suppress\nits electrical conductivity. Finally, the IGZO ONT with a Bi<sub>2</sub>Te<sub>3</sub> layer exhibits optoelectronic characteristics under\nvisible-light irradiation. Under red-light irradiation having a light\nintensity of 5 mW mm<sup>–2</sup>, it exhibits enhanced optoelectronic\ncharacteristics including photoresponsivity, photosensitivity, and\ndetectivity from 19.6 to 3.46 × 10<sup>2</sup> A/W, 4.95 to 1.46\n× 10<sup>8</sup>, and 1.45 × 10<sup>7</sup> to 2.13 ×\n10<sup>12</sup> Jones compared to that without a Bi<sub>2</sub>Te<sub>3</sub> layer, respectively. To confirm reproducibility and uniformity,\nwe fabricated and compared the optoelectronic characteristics of 5\nsamples from batch to batch. Regarding optoelectronic neuromorphic\ncharacteristics, the ONT exhibits short- and long-term memory and\na highly linear relationship between peak synaptic current and pulse\nnumber under red-light pulses. The paired-pulse facilitation index\nwas 208%. To confirm the applicability of artificial visual perception,\na 6 × 6 ONT array demonstrates long-term memory characteristic\nsuccessfully after red-light irradiation with a Y-shaped pattern.\nIn view of stability and reliability, we conducted three potentiation\nprocesses and compared the peak synaptic currents of each potentiation\nprocess.