Heater-Embedded Visible-Light Phototransistor Based on Cd-Doped IGZO Film Fabricated through Microwave-Assisted Sol–Gel Process

A phototransistor with a sol–gel-based Cd-doped indium-gallium-zinc-oxide (IGZO) photoactive sensing channel on a dual-purpose indium-tin-oxide (ITO) substrate (gate electrode and embedded transparent heater) is reported for the first time. The Cd-doped IGZO layer is fabricated in situ by a one-step microwave-assisted sol–gel process with reduced temperature (<125 °C) and time (<15 min). Despite the wide bandgap of the IGZO (≈3.83 eV) channel, visible-light (≈2 eV) photosensing is achieved in the developed phototransistor upon Cd doping owing to the reduced bandgap (≈3.71 eV) and increased density of subgap states associated with oxygen vacancies in the metal–oxygen bonding structure. In addition, the Cd-doped IGZO phototransistor exhibits excellent operational stability (up to 10 000 cycles) and long-term reliability (up to 30 days). Finally, the embedded Joule heater, based on the inherent transparent ITO substrate, significantly improves the recovery characteristics of the IGZO phototransistor owing to relaxation of the photoexcited charges at the oxygen-vacancy-related trap states upon heating, resulting in 100% recovery in a significantly reduced timeframe (≈10 s). These findings pave the way for the development of high-performance, stable, and reliable visible-light phototransistors based on wide-bandgap IGZO active sensing channels with fast and full recovery, expanding their practical applicability of optoelectronics.