Surface and bulk properties of CuGaSe2 thin films |
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| Institution: | 1. Hahn-Meitner-Institut GmbH, Abt. SE 2, Glienicker Strasse 100, Berlin 14109, Germany;2. Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany;1. University of Missouri – St. Louis, Department of Chemistry and Biochemistry & Center for Nanoscience, United States;2. Southern Illinois University Edwardsville, Department of Chemistry, United States;1. Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, Akademgorodok 50, bld. 38, Krasnoyarsk, 660036 Russia;2. Siberian State Aerospace University, Krasnoyarsk 660014, Russia;1. Departamento de Física Teórica, Universidad Autónoma de Madrid (UAM), Campus de Cantoblanco, 28049 Madrid, Spain;2. Instituto de Física Teórica (IFT) UAM-CSIC, Campus de Cantoblanco, 28049 Madrid, Spain;3. Instituto de Física de Buenos Aires UBA & CONICET, Departamento de Física, Facultad de Ciencia Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina;4. Pontificia Universidad Católica Argentina, 1107 Buenos Aires, Argentina;1. Department of Physics, Faculty of Science, Chulalongkorn University, Phyathai Road, Bangkok 10330, Thailand;2. Research Center in Thin Film Physics, Thailand Center of Excellence in Physics, CHE, 328 Si Ayutthaya Road, Bangkok 10400, Thailand |
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| Abstract: | Using complementary techniques, namely X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS), we present a comparative study of the bulk and surface composition in device grade CuGaSe2 (CGSe) thin films. The films were deposited in two stages by an open-tube chemical vapor deposition (CVD) process. The first stage leads to a nearly stoichiometric polycrystalline CGSe film of approximately 1.5 μm thickness. During the second stage the film is annealed in a Ga- and Se-rich atmosphere. While the XRF-data show a nearly stoichiometric integrated film composition, the surface composition, as determined by XPS analysis, is Cu-poor, pointing towards a highly non-stoichiometric surface layer. In addition, sodium was found at the film surfaces. The data are discussed in the framework of an ordered defect compound formation and the formation of a (Cu,Na)–Ga–Se compound at the surface of the CuGaSe2 films. Complementary ultraviolet photoelectron- and inverse photoelectron spectroscopy investigations of the film surface derive a widening of the surface energy band gap up to 2.2 eV in comparison with a bulk energy band gap around 1.65 eV (obtained by optical transmission analysis). The observed data are consistent with our model of a two layer film structure containing a defect-rich near-surface region and a defect-poor bulk. |
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