We have investigated the influence of post-deposition annealing on the optical and electrical properties of c-axis oriented zinc oxide films prepared on sapphire substrates by electron beam evaporation. The ZnO films as-deposited and annealed in air were colourless and transparent in visible range and had sharp ultraviolet absorption edges. It is found that the optical bandgap energy of the films lies in the range of ∼3.27 to ∼3.30 eV depending on the annealing regime. From the analysis of the Urbach tail at the absorption edge, the width of the tail of localized states extending into the bandgap was obtained and a value of 44 meV can be achieved by annealing in air.
Lithium-doped zinc oxide (ZnO) films were prepared on C-plane sapphire substrates by the e-beam deposition technique in vacuum. The dependences of the optical absorption edge characteristics, structural, and photoelectrical properties on Li content (from 0 to 10 at.%) were investigated. It is found that the variations of the energy bandgap E g , the spread in the tail of the band edge (parameter E 0 ), the electrical resistivity ρ, and the lattice constant c with impurity concentration do not have monotonic character. Abrupt jumps of the optical and electrical characteristics were observed as the impurity concentration changed near 0.8 at.% Li. The significant enhancement of photoconductivity response for 0.8 at.% Li-doped ZnO films also correlates with the enhanced electrical resistivity up to 2 × 10 6 Ω cm and the appearance of a photoinjection current.
A new way of preparing Y–Ba–Cu–O (YBCO) high-temperature superconducting (HTSC) materials has been developed using the sol–gel processing technique based on new and convenient precursors that are stable in air and have high compatibility with each other. For the preparation of HTSC materials, instead of unstable copper alkoxides, the use of chelate type copper compounds as highly effective and stable precursors has been suggested. These have been prepared by the reaction of copper hydroxide with the corresponding (mono, di, tri)ethanolamines. A new method of preparing yttrium precursors on the basis of coordination acetylacetonate type polymer has been suggested. A reaction with bidentate type complex forming solvents such as 2-alkoxyethanols results in the formation of the complex type yttrium alkoxides. Superconducting YBCO ceramic materials have been developed, both films (applied on yttrium stabilized zirconia) and powders, using the sol–gel method based on the new yttrium and copper precursors. X-ray and thermal analyses of the synthesized materials have been carried out. The transition temperature into the superconducting state, T(0)c, and the temperature interval of this transition, ΔT, have been found to be T(0)c = 84 and 88 K and ΔT = 4 and 3 K for YBa2Cu3O7−x bulk ceramics and thin films, respectively.
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