AVS 45th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoM

Paper TF-MoM9
Work Function Modification of Indium Tin Oxide

Monday, November 2, 1998, 11:00 am, Room 310

Session: Transparent Conductive Oxides
Presenter: S.M. Tadayyon, University of Western Ontario, Canada
Authors: S.M. Tadayyon, University of Western Ontario, Canada
K. Griffiths, University of Western Ontario, Canada
P.R. Norton, University of Western Ontario, Canada
C. Tripp, Xerox Research Centre of Canada
Z. Popovic, Xerox Research Centre of Canada
Correspondent: Click to Email
Indium-tin-oxide (ITO) is a transparent conducting material widely used in electronic devices such as flat panel displays, solar cells, IR detectors and OLED's where it is used as the hole injecting electrode. It is desirable to have an electrode possessing as high a work function as possible, and so extensive investigations into properties and modification of ITO have been undertaken. The objective of the present study is the possible modification of ITO work function (WF) using evaporated metal overlayers. We have therefore studied gold overlayers because of the high WF of gold, and its inertness. ITO films on glass substrates (resistance ~ 10 Ohms/sq) were cleaned with a UV-ozone treatment before entry into a UHV system. Auger electron spectroscopy (AES) was used to determine the surface composition. The change of work function (WF) of the surface (± 10mV) was determined by a Kelvin probe technique and correlated with the absolute coverage (@theta@) of Au in the range 0<@theta@<2x10@super 16@ Au cm@super -2@ (calibrated by Rutherford backscattering). The morphology of the films was determined by AFM. The original ITO is very smooth (roughness < few nm) and the Au films exhibit grain sizes of ~30 nm. Annealing at 215 °C improved the wetting characteristics. UV-ozone cleaned surfaces exhibited the highest work function. Surprisingly, in sequential Au deposition experiments, the WF decreased to a minimum at ~ 1x10@super 15@ Au cm@super -2@ before increasing again and becoming constant at @theta@ > 5x10@super 15@ Au cm@super -2@. The final WF values were not very different from the non-UV-ozone treated samples. Studies on bulk Au and ITO covered by Au in a single deposition, showed that the low final WF value in the sequential experiments was attributable to adsorption of hydrocarbons from the 5x10@super10@ torr vacuum, and that useful increases in WF are attainable on transparent ITO electrodes