Influence of Metal Impurity Defects on the Electrical and Optical Properties of ITO Films on the PEN Substrates
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1012-Y12-10
Influence of Metal Impurity Defects on the Electrical and Optical Properties of ITO Films on the PEN Substrates Hauk Han1,2, and Terry L. Alford1,2 1
School of Materials, Arizona State University, Tempe, AZ, 85287-8706
2
Flexible Display Center at ASU, Arizona State University, Tempe, AZ, 85287
ABSTRACT Indium tin oxide (ITO) has drawn a great deal of attention due to its potential use as transparent electrodes in organic light emitting diode (OLED) and photovoltaic applications. This work focuses on understanding the role of impurity defects on the electrical conduction and transmittance of ITO. Thin films of ITO with high carrier concentration have been deposited onto polyethylene napthalate (PEN) substrates by electron-beam deposition without introduction of oxygen into the chamber. The influence of air anneals on the electrical and optical properties of ITO/PEN samples can is evaluated in terms of the oxygen content and is explained in terms of changes in the free electron concentrations. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis were used to determine the oxygen content in the film. A Hall effect measurement is used to determine the dependence of electrical properties on oxygen content. The electrical properties of the ITO films such as carrier concentration, electrical mobility, and resistivity abruptly changes after annealing in the air atmospheres. In addition, optical transmittance is improved from 7 to 71 % and optical band gap changes from 3.18 to 3.25 eV after heat treatment. The optical band gap narrowing behavior is because of impurity band and heavy carrier concentration. Metal impurity clusters form in the films as a result of oxygen deficiency and also generate defects and/or impurity states in the band gap and produces an optical band gap shift by merging of these impurity states and conduction band. INTRODUCTION The transparent conducting oxide (TCO) thin films, such as tin oxide (SnO2), indium oxide (In2O3), zinc oxide (ZnO), and their mixture compounds, on polymer substrate have attracted great attention in the optoelectronic industry due to potential application of in flexible optoelectronic and microelectronic devices. Among those TCO films, indium tin oxide (ITO) films have been widely used in optoelectronic and photonic applications due to its excellent high electrical conductivity combined with high transmission in the visible region [1]. Plastic substrates offer many advantages such as light weight, toughness, and flexibility. Style of design freedom of polymer substrates allows roll-up display and roll-to-roll manufacturing.
However plastic substrates are critical to heat processing during device fabrication. Previous results using rf sputtering for deposition of ITO on polymer substrate shows that sputtering can be used to deposit ITO films at room temperatures without any deformation of the polymer substrates [1, 2]. In this paper, samples have been prepared by e-beam evaporation without introduction of any oxygen into the ch
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