Defect-induced optical and electrical property modification in amorphous InGaZnO4 films

We report the physical characteristics of InGaZnO4 films deposited at various temperatures. The films were deposited on Al2O3(0001) substrates using pulsed laser deposition technique. Based on X-ray diffraction and field emission scanning electron microscopy measurements, the crystal structure changed from amorphous to polycrystalline as deposition temperature increased to 550 °C. Furthermore, UV-vis measurements revealed a decrease in tail state i.e. improvement of local ordering, resulting in an increase of optical band-gap energy as deposition temperature increased. The core-level X-ray photoelectron spectra also showed an increase (decrease) in metal-oxide (oxygen deficiency) bond as the deposition temperature increased. The carrier concentration, Hall mobility and conductivity variation with deposition temperature are related to the competition between oxygen deficiency and grain boundary formation.