Artificially Fabricated Subgap States for Visible-Light Absorption in Indium–Gallium–Zinc Oxide Phototransistor with Solution-Processed Oxide Absorption Layer

We present a solution-processed oxide absorption layer (SAL) for detecting visible light of long wavelengths (635 and 532 nm) for indium-gallium-zinc oxide (IGZO) phototransistors. The SALs were deposited onto sputtered IGZO using precursor solutions composed of IGZO, which have the same atomic configuration as that of the channel layer, resulting in superior interface characteristics. We artificially generated subgap states in the SAL using a low annealing temperature (200 °C), minimizing the degradation of the electrical characteristics of thin-film transistor. These subgap states improved the photoelectron generation in SALs under visible light of long wavelength despite the wide band gap of IGZO (∼3.7 eV). As a result, IGZO phototransistors with SALs have both high optical transparency and superior optoelectronic characteristics such as a high photoresponsivity of 206 A/W and photosensitivity of ∼10⁶ under the influence of a green (532 nm) laser. Furthermore, endurance tests proved that the IGZO phototransistor with SALs can operate stably under red laser illumination switched on and off at 0.05 Hz for 7200 s.