Chemical treatment of monocrystalline cadmium telluride and Cd₁₋xMnxTe solid solutions by Н₂О₂–НІ–citric acid etchant compositions

Dissolution of CdTe and Cd₁₋xMnxTe single crystals in aqueous solutions of Н₂О₂–НІ–citric 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

Dissolution of indium arsenide in nitric solutions of the hydrobromic acid

Dissolution of InAs in HNO₃-HBr-H₂O solutions is studied. The surface of equal etching rates is constructed, and the limiting stages of the dissolution process are determined. Depending on the [HNO₃]/[HBr] ratio, InAs dissolution may be limited by kinetic, or diffusion, or combined mechanisms. The dissolution rate of InSb in these solutions is rather low, and the etched surface is covered with a friable sediment. HNO₃ -HBr-H₂O solutions can be employed for a dynamic chemical polishing of InAs with a variable etching rate

Chemical dynamic polishing CdTe and CdxHg₁–xTe single crystals by using solutions of H₂O₂–HCl–tartaric acid system

Dissolution of CdTe and CdxHg₁–xTe single crystals by using solutions of H₂O₂– 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

Chemical-dynamic polishing of semiconductor materials based on Bi and Sb chalcogenides by using HNO₃–HCl solutions

The chemical etching of Ві₂Те₃ and n-(Ві₂Те₃)₀.₉(Sb₂Te₃)₀.₀₅(Sb₂Se₃)0.05 and p- (Bi₂Te₃)₀.₂₅(Sb₂Te₃)₀.₇₂(Sb₂Se₃)₀.₀₃ crystals of solid solutions with HNO₃–HCl etchant compositions was investigated. The dependences of dissolution rate of these semiconductors on etchant composition, stirring, temperature and their shelf-time storage have been studied. It was shown that the process of dissolution of the investigated materials in the polishing solutions HNO₃–HCl is limited by the diffusion stages

CdTe quantum dots precipitation of monodisperse fractions from colloid solutions

CdTe nanocrystals were prepared in aqueous solution by the reaction between Cd²⁺ and H₂Te, 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

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

Electronic structure and band parameters for ZnX (X = O, S, Se, Te)

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to correct the strong correlation of the Zn-3d electrons, and thus improves the agreement with the experimentally established location of the Zn-3d levels. Consequently, it increases significantly the parameters underestimated in the pure LDA calculations.Comment: 7 pages, 3 figures, 2 tables, ICAM-ICMAT conference, 200