Evolution of electrical properties and thin-film transistor characteristics of amorphous indium gallium zinc oxide (IGZO) thin films synthesized by RF sputtering with O-2 plasma immersion has been examined. O-2 plasma immersion results in an enhancement in the Hall mobility and a decrease in the electron concentration; and the transistor performance can be greatly improved by the O-2 plasma immersion. X-ray photoelectron spectroscopy analysis indicates that the effect of O-2 plasma immersion on the electrical properties and the transistor performance can be attributed to the reduction of the oxygen-related defects in the IGZO thin films. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.