Effects of flow rate of oxygen and substrate temperature on the characteristics of IZO thin films for OLEDs

Abstract

This study examined the effects of the O2 flow rate and the substrate temperature on the structural, electrical, and opticalcharacteristics of the IZO thin films intended for use as anode materials in OLEDs (organic light emitting diodes). These IZOthin films were deposited by RF magnetron sputtering at room temperature and 300 oC at various O2 flow rates. To examinethe effects of O2, the O2 flow rate in the argon mixing gas was changed from 0.1 sccm to 0.5 sccm. IZO thin films depositedat room temperature showed an amorphous structure, whereas IZO thin films deposited at 300 oC showed a crystallinestructure with an (222) preferential orientation regardless of the O2 flow rate. The electrical resistivity of the IZO thin filmsincreased with increasing O2 flow rate under Ar + O2. The change in the electrical resistivity with increasing O2 flow rate wasinterpreted mainly in terms of the charge carrier concentration rather than the charge carrier mobility. The electricalresistivity of the amorphous-IZO films deposited at R.T. was lower than that of the crystalline-IZO thin films deposited at300 oC. All the films showed an average transmittance of more than 83% in the visible range. The optical band gap of the IZOfilms increased with decreasing O2 flow rate. The current density and luminance of the OLED devices with IZO thin filmsdeposited at room temperature in 0.1 sccm O2 ambient gas were the highest among the films examined. These properties wereattributed to the improved optical band gap, which plays a major role in the OLED device performance.