Investigation of Infrared Photo-Detection Through Subgap Density-of-States in a-InGaZnO Thin-Film Transistors

Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) are investigated for a possible application to infrared (IR) photodetector through subgap density-ofstates over the forbidden bandgap. The origin of the sub-bandgap(h upsilon < Eg) photo-response in a-IGZO TFTs is due to optically pumped electrons from the photo-responsive subgap states (E-C-E-ph< E-t< E-F). Among the sub-bandgap lights, we investigate the reproducible IR photo-response in a-IGZO TFTs as a photodetector without the persistent photoconductivity(PPC) effect. In this letter, we characterize the IR photo-response mechanism through various optical and electrical measurements on the wavelength, optical power, bias-modulated quasi-Fermi level, and photo-responsive states. This result is expected to provide independent and/or integrated IR detector with transparent substrate combined with a-IGZO TFTs.