A Facile Method Based on Oxide Semiconductor Reduction for Controlling the Photoresponse Characteristic of Flexible and Transparent Optoelectronic Devices

Abstract A facile method is presented involving a reducing agent, sodium dithionite (Na₂S₂O₄), to control the photoresponse characteristics of oxide semiconductors that detect visible‐light. The method exhibits extraordinary potential for fabricating a diverse range of optoelectronic devices. Due to its weak S–S bond, Na₂S₂O₄ generates excessive subgap states and oxygen vacancies in hafnium–indium–gallium–zinc oxide (HIGZO) thin‐film during the reduction treatment (RDT). It is achievable to finely tune the photoresponse characteristic by adjusting the molarity of Na₂S₂O₄, implying superior applicability of RDT into various applications. First, HIGZO phototransistors with photoresponsivity of 626.32 A W⁻¹, photosensitivity of 3.32 × 10⁷, and detectivity of 7.18 × 10¹¹ Jones under 10 mW mm⁻² of red light illumination are fabricated using 0.1 m Na₂S₂O₄. Second, 0.5 m Na₂S₂O₄ is chosen for photomemory‐based neuromorphic devices with a paired‐pulse facilitation index of 142.6% when the input pulse of red light with an intensity of 1 mW mm⁻² is introduced. In addition, major synaptic functions such as short‐term memory and long‐term memory behaviors, originated from persistent photoconductivity and depending on sequential pulse condition, are successfully emulated. These results indicate that RDT can control the photoresponse of oxide semiconductors to expand the applicability of oxide semiconductors without using a light absorption layer.