Electronic structure and optical properties of ZnX (X=O, S, Se, Te)

Electronic band structure and optical properties of zinc monochalcogenides with zinc-blende- and wurtzite-type structures were studied using the ab initio density functional method within the LDA, GGA, and LDA+U approaches. Calculations of the optical spectra have been performed for the energy range 0-20 eV, with and without including spin-orbit coupling. Reflectivity, absorption and extinction coefficients, and refractive index have been computed from the imaginary part of the dielectric function using the Kramers--Kronig transformations. A rigid shift of the calculated optical spectra is found to provide a good first approximation to reproduce experimental observations for almost all the zinc monochalcogenide phases considered. By inspection of the calculated and experimentally determined band-gap values for the zinc monochalcogenide series, the band gap of ZnO with zinc-blende structure has been estimated.Comment: 17 pages, 10 figure

CdTe quantum dots precipitation of monodisperse fractions from colloid solutions

Abstract. CdTe nanocrystals were prepared in aqueous solution by the reaction between Cd 2+ and H 2 Te, obtained electrochemically in a galvanostatic cell, in the presence of thioglycolic acid. Subsequently, we have investigated precipitation of monodisperse fractions of CdTe quantum dots from polydisperse colloid solutions. In addition, the photoluminescence characteristics of these systems were studied in detail

Coulomb correlation effects in zinc monochalcogenides

Electronic structure and band characteristics for zinc monochalcogenides with zinc-blende- and wurtzite-type structures are studied by first-principles density-functional-theory calculations with different approximations. It is shown that the local-density approximation underestimates the band gap and energy splitting between the states at the top of the valence band, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field-splitting energy. Regardless of the structure type considered, the spin-orbit-coupling energy is found to be overestimated for ZnO and underestimated for ZnS with wurtzite-type structure, and more or less correct for ZnSe and ZnTe with zinc-blende-type structure. The order of the states at the top of the valence band is found to be anomalous for ZnO in both zinc-blende- and wurtzite-type structure, but is normal for the other zinc monochalcogenides considered. It is shown that the Zn-3d electrons and their interference with the O-2p electrons are responsible for the anomalous order. The typical errors in the calculated band gaps and related parameters for ZnO originate from strong Coulomb correlations, which are found to be highly significant for this compound. The LDA+U approach is by and large found to correct the strong correlation of the Zn-3d electrons, and thus to improve the agreement with the experimentally established location of the Zn-3d levels compared with that derived from pure LDA calculations

Chemical dynamic polishing CdTe and Cd x Hg 1-x Te single crystals by using solutions of H 2 O 2 -HCl-tartaric acid system

Abstract. Dissolution of CdTe and Cd x Hg 1-x Te single crystals in solutions of H 2 O 2 -HCl-tartaric acid system has been studied. The surfaces of equal etching rates were constructed and the limiting stages of the dissolution process were ascertained. Also determined were the concentration limits for the solutions that can be used for chemical polishing the above-mentioned semiconductor materials

Selective Etching of ZnхCd1-хTe Single Crystals

Selective etching is an express method to identify the defects of crystal structure of semiconductors. It reveals the dislocations density, type of conductivity, crystal’s orientation, inclusions/precipitates, twins. This article is the review of selective etching of ZnxCd1-xTe single crysrals. All informations has been generalized in the table. Qualitative and quantitative compositions of etchants and information about defect structure of Zn<sub>x</sub>Cd<sub>1-x</sub>Te after etchant treatment have been represented in the table. Keywords: chemical etching, solid solutions, selective etching, etchant, etch pits

Selective Etching of ZnхCd1-хTe Single Crystals

Selective etching is an express method to identify the defects of crystal structure of semiconductors. It reveals the dislocations density, type of conductivity, crystal’s orientation, inclusions/precipitates, twins. This article is the review of selective etching of ZnxCd1-xTe single crysrals. All informations has been generalized in the table. Qualitative and quantitative compositions of etchants and information about defect structure of Zn<sub>x</sub>Cd<sub>1-x</sub>Te after etchant treatment have been represented in the table. Keywords: chemical etching, solid solutions, selective etching, etchant, etch pits

Calcium \u2013 Iron \u2013 Oxygen

Calcium \u2013 Iron \u2013 Oxygen in 'iron systems: phase diagrams, crystallographic and thermodynamic data', part of 'Landolt-B\uf6rnstein - Group IV Physical Chemistry: Numerical Data and Functional Relationships in Science and Technology, Volume 11D2: Iron Systems, Part 2'. This document is part of Volume 11 \u2018Ternary Alloy Systems: Phase Diagrams, Crystallographic and Thermodynamic Data\u2019, Subvolume D \u2018Iron Systems\u2019, of Landolt-B\uf6rnstein - Group IV \u2018Physical Chemistry\u2019. It contains crystallographic and thermodynamic data about the ternary alloy system: Ca-Fe-O Landolt-B\uf6rnstein home Volume IV/11D2 Introduction Inde