Electrical Properties of Thin Nitrogen-Doped Ultrananocrystalline Diamond Films
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Electrical Properties of Thin Nitrogen-Doped Ultrananocrystalline Diamond Films V.I. Polyakov1, A.I. Rukovishnikov1, S.M. Pimenov2, J.A. Carlisle3, D.M. Gruen3 1
Institute of Radio Engineering & Electronics, RAS, 11 Mohovaya str., 103907 Moscow, Russia, E-mail: [email protected] 2 General Physics Institute, 38 Vavilova str., 119991 Moscow, Russia 3 Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
ABSTRACT The electrical properties of ultrananocrystalline diamond (UNCD) films of approximately 1µm thickness were studied. UNCD films were deposited on p-type Si substrates from CH4/Ar/N2 gas mixtures using microwave plasma CVD techniques. It was found that the UNCD films with higher nitrogen concentration and higher electron conductivity have substantially higher concentration of shallow levels with activation energy of about 0.05 eV. The change of concentration, activation energy and capture cross-section of nitrogen-induced levels for UNCD films synthesized using different nitrogen concentration in the plasma was studied by charge– based deep level transient spectroscopy. INTRODUCTION Diamond films grown from hydrogen-poor argon/fullerene or argon/methane microwave plasmas are characterized by a microstructure consisting of crystallites with an average size of 310 nm [1-3]. These films are called ultrananocrystalline diamond (UNCD) [3] to distinguish them from other diamond films with submicrometer grain sizes. Using hydrogen-poor growth conditions, the uniform films with few nanometer diamond crystallites throughout their entire thickness can be grown. These UNCD films have a large percentage of atoms at the grain boundary (GB) that reaches 10% for an experimental grain size of 3 nm [1], derived from simple considerations of grain surface to volume ratio. GBs in UNCD are expected to be different from those in microcrystalline diamond that may be a general reason of the observed differences in electrical and optical properties [1,2]. Many of the properties show also a strong dependence on the crystallite size, the fraction of carbon atoms at the GBs, and concentration of incorporated impurities. The effect of incorporated nitrogen atoms on the properties of UNCD is of great interest. The influence of nitrogen-induced defects (levels) has already been well-studied in bulk CVD and natural diamonds [4-6]. Nitrogen atoms that are incorporated at substitutional sites of diamond crystal form deep level with activation energy of about 1.6-1.7 eV (from resistivity measurements as a function of temperature [6]). As compared to impurities in bulk of diamond crystal, impurities in the disordered grain boundaries can have different concentration, geometry, and electronic structure and may drastically change electrical properties of UNCD [7,8]. However, the parameters of nitrogen-induced levels in the UNCD have not yet been determined experimentally. In this paper we report on a study of conductivity and parameters of nitrogen-induced levels in nitrogen-doped UNCD films.
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