Electronic structure and excitonic absorption in BaCuChF (Ch=S, Se, and Te)

Double excitonic absorption peaks are observed in textured BaCuSF and BaCuSeF thin films. The excitonic doublet separation increases with increasing fraction of heavy chalcogen in the thin-film solid solutions, in good agreement with the spin-orbit splitting of the valence bands calculated by density-functional theory. In BaCuSF and BaCuSeF, the excitons have large binding energies (95 and 65 meV, respectively) and can be observed at room temperature. A three-dimensional Wannier-Mott excitonic absorption model gives good agreement between the experimental and theoretical optical properties. Band gaps of BaCuSF and BaCuSeF calculated using the GW approximation agree with experiment. In BaCuTeF, transitions across the lowest direct energy gap and excitonic absorption are suppressed, extending its transparent range

Thin Film Growth and Device Fabrication of Iron-Based Superconductors

Iron-based superconductors have received much attention as a new family of high-temperature superconductors owing to their unique properties and distinct differences from cuprates and conventional superconductors. This paper reviews progress in thin film research on iron-based superconductors since their discovery for each of five material systems with an emphasis on growth, physical properties, device fabrication, and relevant bulk material properties.Comment: To appear in J. Phys. Soc. Jp

Conductive BaCuTeF thin films for transparent contacts for semiconductor electronics

Сhemical composition, structural and electrical properties of the BaCuTeF thin films were investigated. Dependence of the copper excess on the deposition parameters was studied. Excess of copper improves the electrical properties of the films by means of increasing the hole mobility. BaCuTeF thin films can be used as transparent p++-contacts for semiconductor electronics devices

Synthesis and characterization of Sn2+ oxides with the pyrochlore structure

During synthesis of View the MathML source compounds with the pyrochlore structure, some disproportionation of the Sn2+ always occurred. This in turn led to some incorporation of Sn4+ into the octahedral (M) sites of the pyrochlore structure. The actual amount of Sn4+ incorporation was determined by 119Sn Mössbauer spectroscopy for two compounds. Mössbauer spectroscopy also indicated that Sn2+ was strongly displaced from its ideal site in the pyrochlore structure. The compounds Sn2TiNbO6F, Sn2Ti0.9Ta1.1(O,F)7, View the MathML source, and View the MathML source with the pyrochlore structure are yellow to red with band gaps determined from diffuse reflectance ranging from 1.9 to 2.3 eV. The dielectric constant of Sn2+ pyrochlores examined ranged from 31 to 149

Structural and transport properties of CuSc₁₋ₓMgₓO[subscript 2+y] delafossites

Transport and structural properties of Mg-doped and O-intercalated sintered powders and polycrystalline films of CuSc₁₋ₓMgₓO[subscript 2+y] are reported. Substitution of Mg for Sc systematically increases the p-type conductivity in CuSc₁₋ₓMgₓO₂ sintered powders, producing a maximum conductivity of 0.015 S/cm at x≈0.06. A similar level of conductivity is observed in transparent polycrystalline CuSc₁₋ₓMgₓO₂ films at the same doping level. Mg doping causes no significant increase in optical absorption at this level. Intercalation of oxygen into the delafossite structure leads to a much larger increase in p-type conductivity. In powders, the maximum conductivity is 0.5 S/cm at y=0.23 and x=0.05. In oxygen-intercalated films, the maximum conductivity was 25 S/cm, with the transparent films gradually darkening as oxygen is incorporated. Oxygen intercalation increases the a-axis lattice parameter of the delafossite structure in both films and powders, with a much smaller effect on the c-axis parameter. Two distinct phases with y≈0 and y≈0.5 are observed in x-ray diffraction of powders. In films intermediate values of y are observed, often in combination with a distinct y=0 phase. The absorption properties of the powder samples indicate introduction of defects into the 2H polymorph of CuScO₂ and CuSc₁₋ₓMgₓO₂ compared to the 3R polymorph.This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics and can be found at: http://scitation.aip.org/content/aip/journal/jap. Article Copyright (2004) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics