Transport and optical properties of heavily hole-doped semiconductors BaCu2Se2 and BaCu2Te2

Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu2Se2 and BaCu2Te2 are reported. Experimental data include the electrical resistivity. Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for T <= 300 K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2 x 10(18) and 5 x 10(18) cm(-3) near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm(2) V-1 s(-1) for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu2Se2, while no similar feature was observed for BaCu2Te2. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented. (C) 2011 Elsevier Inc. All rights reserved.