Ab initio description of quasiparticle band structures and optical near-edge absorption of transparent conducting oxides
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Ab initio description of quasiparticle band structures and optical near-edge absorption of transparent conducting oxides André Schleifea) Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550; and European Theoretical Spectroscopy Facility
Friedhelm Bechstedt
Institut für Festkörpertheorie und –optik, Friedrich-Schiller-Universität, 07743 Jena, Germany; and European Theoretical Spectroscopy Facility (Received 15 February 2012; accepted 26 April 2012)
Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical absorption spectra (including excitonic effects) for several transparent conducting oxides (TCOs). We discuss HSE1G0W0 results (based on the hybrid exchange-correlation functional by Heyd, Scuseria, and Ernzerhof, and quasiparticle corrections from approximating the electronic self energy as the product of the Green’s function and the screened Coulomb interaction) for band structures, fundamental band gaps, and effective electron masses of magnesium oxide, zinc oxide, cadmium oxide, tin dioxide, tin oxide, indium (III) oxide and silicon dioxide. The Bethe–Salpeter equation (BSE) is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE1G0W0 approach and the solution of the BSE are very well suited to describe the electronic structure and the optical properties of various TCOs in good agreement with experiment.
I. INTRODUCTION
Transparent conducting oxides (TCOs) combine high transparency in the visible spectral range with high electrical conductivity under ambient conditions.1,2 Posttransition-metal compounds such as zinc oxide (ZnO), indium (III) oxide (In2O3), and tin dioxide (SnO2) are typical TCOs as they have large fundamental band gaps rendering these materials transparent into the ultraviolet (UV) spectral range. Due to their very large gaps, especially magnesium oxide (MgO) and silicon dioxide (SiO2) are transparent into the far UV. The gaps can be modified, e.g., not only by alloying ZnO with MgO or cadmium oxide (CdO) (see Ref. 3 and references therein), but also by varying their chemistry, for instance when going from SnO2 to SnO.4 Free carriers, introduced by intentional as well as unintentional doping, are the reason for the remarkable conductivities of the TCOs.5 Prominent examples are aluminum-doped ZnO,6 tin-doped indium oxide,7 antimony-doped SnO2,8,9 or even zinc–indium–tin oxide.10 Bulk TCO materials attract great attention due to their outstanding optical,1 electrical,11–13 and electrochemical14 properties combined with excellent hardness and environmental stability.1 This renders them highly interesting for applications as transparent front contacts for solar a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.147 2180
J. Mater. Res., Vol. 27, No. 17, Sep 14, 2012
http://journals.cambridge.org
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