Effects of Surface Treatment on Work Function of ITO (Indium Tin Oxide) Films

The in uence of inductively coupled plasma (ICP) with CF4 gas on the surface electronic structures of Indium Tin Oxide (ITO) thin lms has been studied by X-ray photoelectron spectroscopy (XPS) and scanning force microscopy (SFM). XPS data showed signicant changes in core-level energies of In 3d5=2, Sn 3d5=2, C 1s and F 1s, implying changes in bonding states of these species after CF4 plasma treatment. Local current maps of ITO surfaces using conducting atomic force microscopy (C-AFM) showed two distinct regions at applied bias of 0.1 V: conducting and nonconducting regions. Local I-V measurements in the conducting regions of as received ITO showed ohmic behavior. Most of the ITO surfaces became non-conducting with Sckottky behavior after surface treatment with CF4 plasma. Kelvin Probe Force Microscopy (KPFM) showed an increase in work function of ITO by 0.8 eV after subsequent CF4 plasma treatment. When ITO flms were exposed in ambient, the work function of ITO decreased gradually, mainly because water molecules were absorbed onto the surfaces. CF4 plasma allowed the making of more negative surfaces with more dangling bonds of uorine ions (F..), and the surfaces with F.. induced electrons from the surfaces to be depleted. Subsequently, this caused the surface band to bend upward. As a result, the work function of ITO flms was increased by the surface treatment, and this helps to inject holes more eciently into the active light-emitting layer from ITO electrodes for improving the performance of organic-light emitting diodes (OLEDs). KCI Citation Count: 25