Effects of flow rate of atmosphere gases on the characteristics of Zn-doped ITO (ZITO) thin films for organic light emitting diodes

Abstract

We have investigated the effect of ambient gases on the structural, electrical, and optical characteristics of Zn -doped indium tin oxide (ZITO) thin films intended for use as anode contacts in organic light emitting diodes (OLED) devices. These ZITO thin films are deposited by radio frequency (RF) magnetron sputtering under different ambient gases ( Ar , Ar + O 2 and Ar + H 2) 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 0.1 sccm to 0.5 sccm and from 0.1 sccm to 1 sccm, respectively. The intensity of the (400) peak in the ZITO thin films increases with increasing H 2 flow rate whilst the (400) peak was nearly invisible in an atmosphere of Ar + O 2. The electrical resistivity of the ZITO thin films increases with increasing O 2 flow rate, whereas the electrical resistivity decreases with increasing H 2 flow rate. The change of electrical resistivity with changes in the ambient gas composition is mainly interpreted in terms of the charge carrier mobility and the charge carrier concentration. All the films show an average transmittance of over 80% in the visible range. The optical bandgap of the ZITO films increases with increasing H 2 flow rates, whereas the optical bandgap of the ZITO films deposited in an O 2 atmosphere decreases with increasing O 2 flow rates. The current density and the luminance of the OLED devices with ZITO thin films deposited in 1 sccm of H 2 ambient gas are the highest among all the films. The optical bandgap energy of ZITO thin films plays a major role in OLED device performance, especially the current density and luminance.