Effects of flow rate of oxygen and hydrogen gases on characteristics of ITO thin films for OLEDs

Abstract

We have investigated the effect of ambient gases on the structural, electrical and optical characteristics of indium tin oxide (ITO) thin films intended for use as anode contacts in organic light emitting diode (OLED) devices. These ITO thin films are deposited by radio frequency magnetron sputtering under different ambient gases (Ar, Ar+O2 and Ar+H2) at 300°C. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0·5 to 5 sccm and from 0·1 to 1 sccm, respectively. The intensity of the (400) peak in the ITO thin films increases with increasing H2 flow rate, while the (400) peak was nearly invisible in an atmosphere of Ar+O2. The electrical resistivity of the ITO thin films increases with increasing O2 flow rate, whereas the electrical resistivity decreases sharply under an Ar+H2 atmosphere and is nearly similar regardless of the H2 flow rate. The change of electrical resistivity with changes in the ambient gas composition is mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. All the films show an average transmittance of >80% in the visible range. The optical band gap of the ITO films increases with increasing H2 flow rates, whereas the optical band gap of the ITO films deposited in an O2 atmosphere decreases with increasing O2 flow rates. The current density and the luminance of the OLED devices with ITO thin films deposited in 1 sccm of H2 ambient gas are the highest among all the films. The optical band gap energy of ITO thin films plays a major role in OLED device performance, especially the current density and luminance.