Correlation between surface and electrical properties of ITO and ITON thin films

Marcel Himmerlich 1Maria Koufaki 2Manolis Sifakis 2Christof Mauder 1Gernot Ecke 1Volker Cimalla 1Juergen A. Schaefer 1Antonis Kondilis 3Mircea Modreanu 4Elias Aperathitis 2Stefan P. Krischok 1

1. Technical University Ilmenau, Institute of Micro and Nanotechnologies, P.O. Box 100565, Ilmenau 98684, Germany
2. Microelectronics Research Group, Institute of Electronic Structure and Laser, Foundation for Research and Technology – Hellas, P.O. Box 1527, 71110 Heraklion, Crete, Greece, P.O. Box 1527, Heraklion 71110, Greece
3. University of Crete, Materials Science and Technology Department, P.O. Box 2208, Heraklion 71003, Greece
4. University College Cork, Tyndall National Institute (TYNDALL), Lee Maltings, Prospect Row, Cork, Ireland

Abstract

Indium tin oxide (ITO) is widely used as an optical as well as an ohmic contact material for many III-V and III-N based optoelectronic devices due to its outstanding properties, like high conductivity and high transparency in a wide range of wavelength. The use of N2 during deposition results in the incorporation of nitrogen into the material leading to indium tin oxynitride (ITON) films with improved optical and electrical performance. In this study we investigate the surface properties of polycrystalline ITO and ITON films using X-ray and ultraviolet photoelectron spectroscopy (XPS,UPS) together with electron energy loss spectroscopy (EELS) as well as Auger electron spectroscopy (AES) depth profiling measurements. Surface changes upon rapid thermal annealing (RTA) are correlated to the optical and electrical properties of the films. The deposition was performed by rf sputtering using an ITO target and Ar or N2 as process gas. Deposition in N2 plasma results in the formation of several types of incorporated nitrogen chemical states, which are mainly located in the first 40 nm of the surface: nitrogen bond to In and Sn, oxynitride bonds as well as unbound nitrogen are found. Comparing the core level spectra of ITO and ITON films, a direct correlation between carrier concentration and existence of an oxygen reduced phase is found. Additionally the UPS spectra of ITON films exhibit a shoulder below the valence band maximum due to the incorporated nitrogen. Upon RTA in N2 the surface properties of ITO films remain unchanged while the desorption of unbound nitrogen from the surface together with a strong segregation of Sn towards the surface at temperatures above 550°C is found for ITON. These processes result in a shift of the absorption edge of ITON towards lower wavelength together with a strong increase of the carrier concentration which influences the contact properties between ITON and p-GaN. The formation of ohmic ITON contacts on p-GaN is examined and discussed.

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Marcel Himmerlich
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-21 16:22
Revised:   2009-06-07 00:44
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