Impurity and phase compositions of the surface of CdxHg1?xTe solid solutions

The results of our studies of the real surface impurity and phase compositions of Cd _x Hg_{1 − x} Te solid solutions and changes in the compositions induced by thermal evacuation and ion bombardment are presented. The impurity and phase compositions of the surface of CdHgTe solid solutions exposed to air included the gases and vapors (CO, O₂, H₂O) and hydrocarbons adsorbed from the atmosphere. Thermal vacuum treatment of the samples at 615 K led to surface purification from organic impurities, oxygen, water, and mercury microinclusions. The Cd _x Hg_{1 − x} Te sample surface was completely cleaned and its stoichiometric composition achieved by ion etching to a depth of 100 ?.     

CdTe and anodic oxides on Hg1−xCdxTe: interface and compositional analysis using Rutherford backscattering spectroscopy

The composition and interfacial region has been studied for CdTe and anodic oxides deposited/grown on Hg_1?xCd_xTe using Rutherford backscattering spectroscopy. The interfacial region for the CdTe/Hg_1?xCd_xTe sample was found to be ～35 nm, in which out‐diffusion of Hg was observed. The interfacial region in the case of anodic oxides/Hg_1?xCd_xTe was found to be very small, <10 nm (of the order of experimental resolution), in which the Hg concentration increases steeply and the oxygen concentration decreases. Passivant and bulk compositions also have been obtained in both cases. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and X-ray diffraction of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> Te solid solutions

The Cd _x Hg_{1 − x} Te solid solutions were synthesized by combining two methods: immersion of CdTe single crystals in liquid mercury and thermal homogenization in mercury vapors. The samples obtained were studied by X-ray diffraction and X-ray fluorescence analyses. Nonstoichiometric cadmium microinclusions were shown to present in the initial CdTe single crystals and the solid solutions synthesized. The samples annealed in mercury vapors have smaller unit cell volumes than unannealed samples.     

Solubility of cadmium in lead tellurides

The solubility of cadmium in PbTe was determined using microhardness and hydrostatic density measurements and by electron microscopy and electron probe microanalysis. All these methods indicate that the existence region of Pb_{1 − x} Cd _x Te solid solutions (ss) extends to x = 0.08 at 670°C. As the cadmium concentration of the solid solution increases, microhardness shifts up, whereas density shifts down.     

Combined adsorption of ammonia and oxygen on the surface of solid solutions of CdxHg1 ? xTe

The adsorption of ammonia, oxygen, and the NH₃ + O₂ mixture on solid solutions Cd _x Hg_{1 − x} Te is studied. The low adsorbability of the mixture, as compared to that of the individual components, is established. Conclusions are drawn as to the nature of its active centers. Schemes for the combined adsorption of ammonia and oxygen are proposed. The temperature areas of tentatively highest catalytic activity of CdTe and CdHgTe in the reaction of ammonia oxidation are established. The formation of gaseous nitrogen in the final products is demonstrated. The degree of ammonia’s transformation into nitrogen is 97–99%. It increased with a rise in temperature and did not depend on the initial ammonia concentration.     

Determination of the stoichiometry of semiconductor systems of the type CdvHg1?vSe and CdxHg1?xTe by X-ray fluorescence spectrometry

Summary Semiconductors of the composition Cd _v Hg_1–v Se and Cd _x Hg_1–x Te are gaining growing industrial interest. The energy gap between the bands of such systems depends significantly on the magnitude of the mole fractions v and x. X-ray fluorescence analysis of acid solutions of these crystals is a simple and precise procedure to determine the stoichiometry. Sample preparation, calibration series and results are discussed.

---

Bestimmung der Stöchiometrie von Halbleitersystemen des Typs Cd_vHg_1–vSe und Cd_xHg_1–xTe, durch Röntgenfluorescenz-Spektrometrie

Zusammenfassung Halbleiter der Typen Cd _v Hg_1–v Se und Cd _x Hg_1–x Te gewinnen zunehmend industrielles Interesse. Der Energieabstand der Bänder in solchen Systemen hängt entscheidend von der Größe der Molenbrüche v und x ab. Ein einfaches und sicheres Analysenverfahren zur Ermittlung der Stöchiometrie ist die Röntgenfluorescenzanalyse von sauren Lösungen dieser Kristalle. Die Probenvorbereitung, Eichreihen und Resultate werden diskutiert.

Delegated to Central Institute of Analytical Chemistry, Nuclear Research Establishment (KFA), Jülich, FRG.     

Magneto‐Optical Studies of HgTe/HgxCd1−xTe(S) Core–Shell Nanocrystals

The synthesis and magneto‐optical properties of HgTe nanocrystals capped with Hg_xCd_1?xTe(S) alloyed shells have been investigated. The magneto‐optical measurements included the use of optically detected magnetic resonance (ODMR) and circular polarized photoluminescence (CP‐PL) spectroscopy. The PL spectra suggest the existence of luminescence events from both the core HgTe and the Hg_xCd_1?xTe(S) shells. The continuous‐wave (cw) and time‐resolved ODMR measurements revealed that the luminescence at the shell regime is associated with a trap‐to‐band recombination emission. The electron trap is comprised of a Cd–Hg mixed site, confirming the existence of an alloyed Hg_xCd_1?xTe(S) composition. The ODMR data and the CP‐PL measurements together revealed the g‐values of the trapped electron and the valence band hole.     

Chemical interaction of CdTe and Cd1? x Zn x single crystals with aqueous H2O2 + HBr + Citric acid solutions

The chemical etching of single crystals of CdTe and Cd_1−x Zn _x Te solid solutions in bromine-evolving aqueous H₂O₂ + HBr + citric acid solutions is considered. Simplex design of experiments is used to construct the projections of etching rate isosurfaces and to map the polishing and nonpolishing composition regions. Dissolution in the polishing etchants is diffusion-controlled. As the zinc content of Cd_1−x Zn _x Te is raised, the etching rate increases; the boundaries of the polishing region do not change to any significant extent. The polish composition and the dynamic chemical polishing conditions are optimized for the semiconductors examined. Original Russian Text ? Z.F. Tomashik, I.I. Gnativ, V.N. Tomashik, I.B. Stratiichuk, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1234–1238.     

New organosols of nickel sulfides,palladium sulfides,manganese sulfide,and mixed metal sulfides and their use in preparation of semiconducting polymer-metal sulfide composites

Organosols of NiS, PdS, and MnS in N,N-dimethylformamide were prepared by reaction of the metal acetate with H₂S. Organosols of mixed-metal sulfides (Zn _x Cd_1–x S, Hg _x Cd_1–x S, Hg _x Cu_1–x S, Cd _x Mn_1–x S, Hg _x Mn_1–x S, Hg _x Cd_1–x S, and Mn _x Zn_1–x S) were similarly obtained by reaction of mixtures of the metal salts with H₂S. The organosol of Zn_0.5Cd_0.5S contained particle with two particle size distributions centered at 6.5 nm and 29 nm, as revealed by Ar laser-scattering analysis. The metal sulfides are recovered by addition of Et₂O to the organosols. Zn _x Cd_1–x S thus obtained shows magnetic susceptibility in the range 0.5×10^–6–2.3×10^–6 emug^–1 depending on thex value. Addition of polymers to the organosols affords semiconducting films of metal sulfide-polymer composites.     

Characterization of native and heterooxide layers on compound semiconductors by combined use of surface analysis methods

Summary Structure, formation and interface reactions of anodic oxides and SiO₂ on Cd_xHg_1–xTe have been studied by means of SIMS, AES, XPS, TDMS and the electron microprobe as an example for the application of surface analysis to compound and semiconductor passivation systems.

---

Charakterisierung von Eigenoxid- und Heterooxidschichten auf Mehrkomponentenhalbleitern durch kombinierten Einsatz oberflächenanalytischer Verfahren

Zusammenfassung Aufbau, Bildungsmechanismus und Grenzflächenreaktionen von anodischen Oxiden und Quarz auf Cd_xHg_1–xTe wurden mit SIMS, AES, XPS, TDMS, SNMS und der Elektronenstrahlmikrosonde untersucht.

     

Effect of annealing atmosphere on structural,optical and electrical properties of Al-doped Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O thin films

1 at.% Al-doped Zn_1−x Cd _x O (x = 0–8 at.%) thin films were prepared on glass substrates by sol–gel method. The codoping films retained the hexagonal wurtzite structure of ZnO, and showed preferential c-axis orientation. The effect of annealing ambient (in vacuum and nitrogen) on the optical and electrical properties of (Cd,Al)-codoped ZnO films were investigated using transmission spectra and electrical measurements. The transmittances of the codoping films were obviously degraded by vacuum annealing to 50–60 %, but enhanced to 70–80 % after nitrogen annealing. The carrier concentration and Hall mobility both increased, and resistivity decreased with narrowing band gap of Al-doped Zn_1−x Cd _x O, below different critical concentrations x = 4 % (in vacuum) and x = 6 % (in nitrogen). It is revealed that the conductivity is also improved by Cd doping along with band gap modification. The variations in optical and electrical properties are ascribed to both the changes of the crystallinity and concentration of oxygen vacancies under different ambient. In view of transmittance and conductivity, nitrogen annealing might be a more effective post-annealing way than vacuum annealing for our (Cd,Al)-codoped ZnO films to meet the requirements of transparent conducting oxide (TCO).     

The kinetics of low-temperature liquid phase epitaxy in the Zn-Cd-Te system

The kinetic corrections for the supersaturation of the initial liquid phase providing the preparation of Zn _x Cd_{1 − x} Te solid solution layers at low deposition temperatures (500–600°C) were found. The results of kinetic modeling were in satisfactory agreement with the experimental data. It was shown that the inclusion of corrections for supersaturation of the initial liquid phase to the data on phase equilibria in the Zn-Cd-Te system was necessary for finding the temperature-time conditions of the crystallization of layers with the required composition.     

Spectroscopic investigations on II–VI-semiconductor nanocrystals and their assemblies

This review points out that (magneto-)optical measurements may help to shine light on the recombination processes taking place in semiconductor nanocrystals. The surface capping with thiols creates a CdS shell around CdTe cores and forms a Cd site that is not fourfold-coordinated at the surface. It is pointed out how specific cappings such as thio-amines and thio-acids assist in coupling NCs and how we may distinguish between NC–NC interactions via electrostatic and covalent linking with the aid of the optical measurements. Furthermore, with static and time-resolved ODMR studies on IR-active core-shell HgTe/Hg _x Cd_1−x Te(S) particles it is demonstrated how the nature of the recombination emission being associated with a Cd–Hg mixed site is elucidated and by this yielding structural information on the NC core-shell interface. With these examples we show that and how nanomaterials of probable technological interest are studied beneficially with advanced spectroscopic techniques.     

Potassium–conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> solid electrolytes

Solid electrolytes with potassium-cation conductivity in the K_{1 − 2x} Pb _x GaO₂ system were synthesized and studied. It was found that solid solutions based on potassium monogallate are formed in a wide range of compositions. They contain vacancies in the potassium sublattice that provide for high conductivity of electrolytes. The relationship is considered between electric characteristics of solid electrolytes and the composition and structure of solid solutions. The results are compared to the earlier obtained data for similar solid electrolytes based on potassium monoaluminate and monoferrite.     

Ferromagnetism study of Co<Subscript>0.2</Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>0.8−<Emphasis Type="Italic">x</Emphasis></Subscript>O films prepared by the sol–gel method

Co_0.2Mg _x Zn_0.8−x O films prepared with different molar ratio of magnesium acetate to zinc acetate were deposited on substrates by the sol–gel technique. X-ray diffraction, photoluminescence (PL) and ferromagnetism measurements were used to characterize the Co_0.2Mg _x Zn_0.8−x O diluted magnetic semiconductors. The acceptor-like defects were determined in the PL band and the intensity of the acceptor-related PL increased with increasing Mg concentration. Therefore, an increase in the number of the acceptor-like defects (zinc vacancies especially) in the Co_0.2Mg _x Zn_0.8−x O film may lead to the enhancement of the magnetic properties. It is worth noting that changes in Mg concentration and the number of the acceptor-like defects are important issues for producing strong ferromagnetism Co_0.2Mg _x Zn_0.8−x O films prepared by the sol–gel method.     

Solid Potassium-Conducting Electrolytes in the System K2 ? 2xAl2 ? xPxO4

New high-conductance potassium-cation solid electrolytes based on potassium aluminate are synthesized by means of partial substitution of five-charged phosphorus cations for three-charged aluminum cations and investigated. The maximum conductivity in the system K_{2 − 2x} Al_{2 − x} P _x O₄ is found to equal 5 × 10⁻³ S cm⁻¹ at 200°C and ∼1 S cm⁻¹ at 700°C, which is one of the best values for potassium solid electrolytes. The principal factors responsible for the high conductance are the stabilization of a high-temperature form of potassium aluminate and the formation of additional vacancies in the potassium sublattice, which occurs during the substitution process Al³⁺ → P⁵⁺ + 2V _K ^′ . __________ Translated from Elektrokhimiya, Vol. 41, No. 12, 2005, pp. 1501–1504. Original Russian Text Copyright ? 2005 by Burmakin, Shekhtman.     

Tysonite-type solid solutions in the BiF<Subscript>3</Subscript>-BiOF-BaF<Subscript>2</Subscript> system: Polymorphism and anionic conductivity

Tysonite solid solutions Bi_1−x Ba _x O _y F_3−x−2y in the BiF₃-BiOF-BaF₂ system were obtained by solid-phase synthesis in sealed copper tubes in an argon atmosphere at 873 K with subsequent quenching. The solid solutions were studied by X-ray diffraction, electron diffraction, and impedance spectroscopy. On the basis of X-ray powder diffraction data, the homogeneity ranges of the tysonite solid solutions were determined and the scheme of their location in the BiF₃-BiOF-BaF₂ system at 873 K was suggested. Aliovalent substitutions in both the cation and anion sublattices Ba²⁺ → Bi³⁺ and O²⁻ → F⁻ made it possible to vary the concentration of anion vacancies. It was found that, at a high concentration of anion defects at 873 K, the hexagonal tysonite modification with space group P6₃/mmc is stable. With a decrease in the defect concentration, the trigonal tysonite modification with space group $ P\bar 3c1 $ P\bar 3c1 becomes stable. An ordered monoclinic tysonite-type modification BiO _y F_{3 − 2y} (0.13 < y < 0.23) was revealed. For the homogeneity ranges of all tysonite phases, dependences of the unit cell parameters and conductivity on the composition along the sections with a constant barium or oxygen content were reported. The most probable location of oxygen anions and anion vacancies in the tysonite structure is discussed.     

Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium cobaltites

The method of isotopic exchange was used to study the kinetics of oxygen exchange and diffusion in complex oxides of La_{1 − x} Sr _x Co_{1 − y} Fe _y O_{3 − δ} (x = 0.0, y = 0.0; x = 0.6, y = 0.2, 0.4). The rates of oxygen interfacial exchange and its diffusion coefficient were determined for LaCoO_{3 − δ} at the pressure of 5 torr in the temperature range of 600–850°C and at the temperature of 700°C in the pressure range of 1–70 torr. The contributions of the three exchange types were calculated. The order of the dependence of the interfacial exchange rate on the oxygen pressure was 0.51 ± 0.01. In the case of La_0.4Sr_0.6Co_{1 − y} Fe _y O_{3 − δ} (y = 0.2, 0.4) in the temperature range of 600–900°C at the oxygen pressure of 10 torr, the oxygen exchange rates and diffusion coefficients were determined in the material bulk and in the subsurface region; contributions of the three types of exchange were calculated. The paper considers the mechanism of oxygen exchange and diffusion as compared to nonstoichiometry in the oxygen sublattice of the La_{1 − x} Sr _x Co_{1 − y} Fe _y O_{3 − δ} oxides.     

The structure, nonstoichiometry, and thermodynamic characteristics of oxygen in strontium ferrite doped with niobium, SrFe1 ? xNbxO3 ? δ

The influence of doping with niobium on the structure and oxygen nonstoichiometry of strontium ferrite SrFe_{1 − x} Nb _x O_{3 − δ} (x = 0.05, 0.1, 0.2, 0.3, and 0.4) was studied. The content of oxygen in the doped derivatives was determined by coulometric titration as a function of temperature (650–950°C) and oxygen partial pressure in the gas phase (10⁻⁴−1 atm). The partial molar enthalpies Δ(x, δ) and entropies Δ(x, δ) of oxygen in SrFe_{1 − x} Nb _x O_{3 − δ} were calculated. An analysis of Δ(x, δ) dependences showed that the model of a random distribution of ions and vacancies over accessible sites in the oxygen sublattice allowed the experimental data to be described satisfactorily. An increase in the partial enthalpy Δ(x, δ) as nonstoichiometry δ decreased was indicative of weak repulsive interactions between oxygen ions in the structure of SrFe_{1 − x} Nb _x O_{3 − δ}. Original Russian Text ? P.V. Anikina, A.A. Markov, M.V. Patrakeev, I.A. Leonidov, V.L. Kozhevnikov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 811–817.     

Thermochemical Properties and Vapor Growth of Hg1-xCdx Te on CdTe

Based on a thermodynamic analysis, the vapor phase of the Hg_1-xCd_xTe—HgI₂—CdTe epitaxy system consists predominantly of Hg(g) and HgI₂(g) through which nutrient species migrate from the source to the CdTe substrate. Growth experiments in the 590° → 535°C temperature gradient showed that Hg_1-xCd_xTe layers can be grown on CdTe substrates using a preannealed, ternary source material in the presence of HgI₂.