Effects of postannealing in ozone environment on opto-electrical properties of Sn-doped In2O3 thin films

Effects of postannealing on electrical, optical and chemical properties in Sn-doped In2O3 (ITO) thin films are studied in the case when the annealing is carried out in ozone-incorporated oxygen atmosphere [O3]. The results are compared to the cases of annealing with the conventional reactive gases, pure oxygen [O2] and ambient air [Air]. The ITO films were deposited by electron-beam evaporation on polyester at room temperature, followed by postannealing at 150 °C for annealing time up to 120 min. Evidence is obtained that the optical transmittance and resistivity of films can be improved more significantly in the order of [O3]>[O2]>[Air] upon annealing for 60 min, though the effects of [O3] and [O2] become comparable by further annealing. A rapid initial fall in the resistivity observed in the case of [O3] is dominated by a large increment in carrier density, while the contribution from the carrier mobility becomes more evident for longer annealing time. The oxygen content relative to indium in the middle region of the films, determined from X-ray photoemission study, seems to be correlated with the behavior of the opto-electrical properties upon postannealing. The enhanced improvement of those properties by the ozone treatment could be attributed to its strong oxidizing ability.