Visible-Light-Stimulated Optoelectronic Neuromorphic Transistor Based on Indium–Gallium–Zinc Oxide via Bi₂Te₃ Light Absorption Layer

To emulate a visual perception system, a bismuth telluride (Bi 2 Te 3 )/indium–gallium–zinc oxide (IGZO) heterostructure is introduced for optoelectronic neuromorphic transistors (ONTs). Amorphous IGZO is applied as a channel layer to exhibit low off-current, high mobility, and persistent photoconductivity, enabling light-stimulated neuromorphic characteristics. The atomic ratio of In/Ga/Zn was 9.4:9.8:5.2. For a light absorption layer, Bi 2 Te 3 is applied due to a small bandgap, high photoresponse, and carrier concentration. However, conventional optoelectronic devices using Bi 2 Te 3 exhibit insufficient performance owing to their excessive conductivity. To resolve the constraint, the oxidation of Bi 2 Te 3 is performed to suppress its electrical conductivity. Finally, the IGZO ONT with a Bi 2 Te 3 layer exhibits optoelectronic characteristics under visible-light irradiation. Under red-light irradiation having a light intensity of 5 mW mm –2, it exhibits enhanced optoelectronic characteristics including photoresponsivity, photosensitivity, and detectivity from 19.6 to 3.46 × 10 2 A/W, 4.95 to 1.46 × 10 8, and 1.45 × 10 7 to 2.13 × 10 12 Jones compared to that without a Bi 2 Te 3 layer, respectively. To confirm reproducibility and uniformity, we fabricated and compared the optoelectronic characteristics of 5 samples from batch to batch. Regarding optoelectronic neuromorphic characteristics, the ONT exhibits short- and long-term memory and a highly linear relationship between peak synaptic current and pulse number under red-light pulses. The paired-pulse facilitation index was 208%. To confirm the applicability of artificial visual perception, a 6 × 6 ONT array demonstrates long-term memory characteristic successfully after red-light irradiation with a Y-shaped pattern. In view of stability and reliability, we conducted three potentiation processes and compared the peak synaptic currents of each potentiation process.