An angular dependent X-ray photoemission study of Indium-tin-oxide surfaces
- PDF / 185,138 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 194 Views
V1.7.1
An angular dependent X-ray photoemission study of Indium-tin-oxide surfaces H.H. Fong, W.J. Song, and S.K. Soa) Department of Physics and Center for Surface Analysis and Research Hong Kong Baptist University, Hong Kong, P.R. China ABSTRACT The surface properties of indium-tin-oxide (ITO) thin films treated by UV ozone or plasma were analyzed by angular dependent X-ray photoelectron spectroscopy (ADXPS) and by ultraviolet photoemission (UPS). The chemical composition, chemical states and the work function of the ITO surfaces were deduced. Our analysis indicate that ITO surface is Sn-rich. Both UV ozone and O-plasma treatments are most effective in removing surface hydrocarbon. Among all treatments, O-plasma treated surface achieved the highest work function of 4.4eV, whereas argon ion sputtered surface had the lowest work function of 3.9eV. Both O-plasma and UV ozone treatments increase the surface oxygen concentration. It is proposed that O2- ions diffuse into ITO. The diffusion length is about 50Å as deduced from ADXPS. The stoichiometry of the surface is the major factor in controlling the surface work function of ITO. A surface band bending model is proposed to account for the change of work function due to “oxidized” ITO surface after UV-ozone or oxygen plasma treatments. INTRODUCTION Indium-tin-oxide (ITO), a highly degenerate n-type semiconductor, is commonly used as anode contact in electroluminescent (EL) devices such as organic light-emitting diodes (OLEDs) and polymer light-emitting diodes (PLEDs). Commercially, ITO is fabricated by Sn-doped In2O3 (bandgap ~3.8eV) with In:Sn ratio of 9:1. Prior to device fabrication, surface treatment of ITO is crucial and necessary in order to improve the device luminous and current efficiencies. [1] Improvement of hole injection from ITO to the hole transporting layer (HTL) is a common concern. The potential barrier between ITO and HTL limits hole injection from ITO to the HTL due to energy level difference between the work function of ITO (φITO) and the highest occupied molecular orbita (HOMO) of the HTL. This barrier can be minimized by proper surface treatments before coating organic materials. In our studies, plasma and UV-ozone treatments on ITO were investigated by using spectroscopic techniques. Results illustrate the ITO surface stoichiometry (
Data Loading...
