Photosensitivity of amorphous IGZO TFTs for active-matrix flat-panel displays

We studied the optical and electrical properties of the amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). To develop a-IGZO density-of-states model, intrinsic a-IGZO optical properties such as optical band gap and Urbach energy, and TFT characteristics under illumination are investigated During the a-IGZO TFTs illumination with the wavelengths ranging from 460 to 660 nm, the off-state drain current only slightly increases while a large increase was observed for the wavelength below 400 nm. Threshold voltage and subthreshold swing are also only slightly modified between 460 to 660 nm, while field-effect mobility is almost unchanged in the investigated photon energy range. The observed results are consistent with the a-IGZO optical energy band gap of about 3.05 eV. This study suggest that the a-IGZO TFTs are light sensitive above 3.0 eV and photogenerated electrons are more mobile than holes within device channel region.