52 research outputs found
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
Polishing etchant compositions for the chemical treatment of the PbTe and Pb1–xSnxTe solid solutions single crystals and methods for their processing. Review
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