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.