The influence of illumination on the electrical characteristics of amorphous indium-zinc oxide (a-IZO) thin-film transistors (TFTs) has been investigated. The electrical properties are found to depend significantly on the active thickness (TIZO) of the a-IZO TFT. The active thickness is seen to play a major role in the carrier transport mechanism. Based on the carrier fluctuation model, the low-frequency noise (LFN) characteristics of a-IZO devices of varying thicknesses were evaluated before as well as after illumination. Similar to the results of DC and capacitance-voltage (C-V) measurements, the LFN characteristics too show that the light-induced carrier transport becomes significantly enhanced for relatively thick (T-IZO >= 60 nm) a-IZO devices. (C) 2014 AIP Publishing LLC.