Properties Of Hg Research Articles

Theoretical investigations of the structural, electronic and optical properties of Hg1−xCdxTe alloys

The structural, electronic and optical properties of mercury cadmium telluride (Hg1−xCdxTe; x = 0.0, 0.25, 0.5, 0.75) alloys are studied using density functional theory within full-potential linearized augmented plane wave method. We used the local density approximation (LDA), generalized gradient approximation (GGA), hybrid potentials, the modified Becke–Johnson (LDA/GGA)-mjb and Hubbard-corrected functionals (GGA/LDA + U), for the exchange-correlation potential (Eex). We found that LDA functional predicts better lattice constants than GGA functional, whereas, both functionals fail to predict the correct electronic structure. However, the hybrid functionals were more successful. For the case of HgTe binary alloy, the GGA + U functional predicted a semi-metallic behaviour with an inverted band gap of −0.539 eV, which is closest to the experimental value (−0.30 eV). Ternary alloys, however, are found to be semiconductors with direct band gaps. For the x = 0.25 and 0.50, the best band gaps are found to be 0.39 and 0.81 eV using LDA-mbj functional, whereas, the GGA-mbj functional predicted the best band gap of 1.09 eV for Hg0.25Cd0.75Te alloy, which is in a very good agreement with the experimental value (1.061 eV). The optical properties of the alloys are obtained by calculating the dielectric function ɛ(ω). The peaks of the optical dielectric functions are consistent with the electronic gap energies of the alloys.

Effect of annealing on the kinetic properties and band parameters of Hg1−x−y Cd x Eu y Se semiconductor crystals

The results of studies of the kinetic properties of Hg1 − x − yCdxEuySe semiconductor crystals in the ranges of temperatures T = 77–300 K and magnetic fields H = 0.5–5 kOe before and after heat treatment of the samples in Se vapors are reported. It is established that annealing of the samples in Se vapors induces a decrease in the electron concentration. From the concentration dependence of the electron effective mass at the Fermi level, the band gap, the matrix element of interband interaction, and the electron effective mass at the bottom of the conduction band are determined.

Thermal, spectral and diffraction properties of Hg(II)-exchanged montmorillonite with alkylamines

Many papers have been published concerning the influence of different steric properties of metylamine, dimethylamine and trimethylamine on the type of interactions with different exchanged montmorillonite and their properties. The most effective active sites in montmorillonite are placed between two silicate layers, where the naturally occurring cations can easily be replaced by heavy metals and organic groups. Mercury is one of the most serious contaminants in environment. All forms of mercury are poisonous; however, organic mercury species are the most dangerous. It is harmful even in very small amount and presents a significant environmental threat. The results of thermogravimetry, differential thermogravimetry, X-ray powder diffraction and IR spectroscopy analysis show that methyl, dimethyl and trimethylamines are intercalated into the interlayer space of Hg-MMT. The effect of different steric properties of studied alkylamines is evident.

Магнитные и кинетические свойства кристаллов Hg1–x–yCdxDyySe

This paper presents research results on the magnetic and kinetic properties of Hg1–x–yCdxDyySe crystals. The coefficient of thermoelectric figure of merit of Hg1–x–yCdxDyySe crystals is determined on the basis of the temperature dependence of electrical conductivity and thermoelectric power. The temperature dependence of the magnetic susceptibility ??has the form typical for paramagnets and decreases with the temperature increase. The growth of ? with the decrease of T results from the decrease in the disorienting effect of thermal vibrations of the atoms in crystal lattice on orientation of the magnetic moments of Dy in magnetic field. The authors have established that the characteristics of the magnetic susceptibility result from the presence of clusters with different sizes. The characteristic properties of the changes in kinetic coefficients with temperature variation for Hg1–x–yCdxDyySe samples suggests that vacancies in the Se sublattice and interstitial mercury mainly affect the transport phenomena in these crystals. It is known that mercury chalcogenides and solid solutions based on mercury interstitials and vacancies in the chalcogen sublattice are donors. The temperature dependence of the electrical conductivity for Hg1–x–yCdxDyySe are metallic in character, that is s decreases with increasing temperature due to decreasing mobility of electrons, the Hall coefficient of the crystals Hg1–x–yCdxDyySe does not depend on temperature, which is associated with the degeneracy of the electron gas. Thermoelectric power for Hg1–x–yCdxDyySe samples is negative and its absolute value increases with the temperature increase due to reduction in the degree of degeneracy of the electron gas. Research results indicate prospects of the application of Hg1–x–yCdxDyySe crystals in spintronics devices.

Optical coefficients of Hg1 − x − y Cd x Eu y Se crystals

Optical properties of Hg 1- x - yCdxEuySe crystals grown by the Bridgman method have been investigated based on the independent reflectance and transmittance measurements, which were performed on a Nicolet 6700 spectrometer at T = 300 K in the wavelength range 0.9 ≤ λ ≤ 26.6 μm. The values of refrac� tive index n, absorption index k, and absorption coefficient α have been determined for the crystals studied. Based on the dependences α = f(hν), the presence of direct allowed interband optical transitions in the crys� tals is established and the bandgap values are determin ed. The influence of temperature on the transmittance and band gap are investigated in the range T = 114-300 K.

Optical Properties of Hg1–x–y Cd x Dy y Se Crystals

Results of investigations of the optical properties of Hg1–x–yCdxDyySe crystals by the Bridgeman method are presented. Based on independent measurements of the reflection and transmission coefficients with a Nicolet 6700 spectrometer at Т = 300 K for wavelengths 0.9 ≤ λ ≤ 26.6 μm, values of the refractive and absorption indices and of the absorption coefficient are determined for the examined crystals. From the dependences α = f(hν) it is established that direct interband optical transitions are allowed in the crystals, and values of the gap width are determined. The effects of the temperature on the transmission coefficient and on the gap width at Т = 118–297 K are investigated.

Magnetic, optical, and kinetic properties of Hg1 − x − y Mn x Dy y Te crystals

We have studied the magnetic, optical, and kinetic properties of Hg1 − x − yMnxDyyTe crystals. The behavior of their magnetic susceptibility can be accounted for by the presence of clusters of various sizes. The Hg1 − x − yMnxDyyTe crystals are shown to be n-type. Absorption data are used to determine the optical band gap of the crystals.

Hydrodynamic Simulation of Drift Mobility in N-Hg<sub>0.8</sub>Cd<sub>0.2</sub>Te

In this paper, the transport properties of Hg0.8Cd0.2Te have been investigated at 77 K using the hydrodynamic model. We remarked that ionized impurity scattering mechanism plays a dominant role in this material at low electric field. The drift velocity, mean energy and drift mobility are determined as functions of the electric field strength. Comparison is made with Monte Carlo calculations and experimental results. The obtained velocity-field curve is in good agreement with reported experimental data.

Combined Effect of N-Acetyl Cysteine, Zinc, and Selenium Against Chronic Dimethylmercury-Induced Oxidative Stress: A Biochemical and Histopathological Approach

Mercury (Hg), widely used in industry, is a great environmental health problem for humans and animals. Despite several reports regarding Hg toxicity, there is scarcity of data on its toxic manifestations on Sprague Dawley rats under realistic exposure conditions. Experimental studies have shown that sulphur-containing antioxidants have beneficial effects against the detrimental properties of Hg. The present work was aimed to study the therapeutic potential of combined administration of N-acetyl cysteine (NAC; 2 mmol/kg ip), zinc (Zn; 2 mmol/kg po), and selenium (Se; 0.5 mg/kg po) against dimethylmercury (DMM; 1 mg/kg po)-intoxicated male rats for 12 weeks. Exposure to DMM caused significant alterations in cytochrome P450 (CYP) activity, microsomal lipid peroxidation, and proteins. Activities of transaminases (aspartate aminotransferase/alanine aminotransferase), alkaline phosphatase, and lactate dehydrogenase in serum, as well as activities of CYP enzymes aniline hydroxylase (AH), amidopyrine-N-demethylase (AND) in liver microsomes and activities of acid phosphatase, alkaline phosphatase, glucose-6-phophatase, and succinic dehydrogenase in the liver and kidney, were significantly altered after DMM administration. DMM exposure also induced severe hepato-renal alterations at the histopathological level. NAC, along with Zn and Se, dramatically reversed the alterations in all of the variables more toward control. The study results conclude that protective intervention of combined treatment of NAC, along with Zn and Se, is beneficial in attenuating DMM-induced systemic toxicity.

Pressure dependent mechanical and thermodynamical properties of Hg0.91Mn0.09Te semiconductor

The mechanical, thermodynamical and elastic properties of Hg0.91Mn0.09Te compound are calculated by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb, three body force parameter, the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction. The estimated values of phase transition pressure have revealed reasonably good agreement with the available experimental data on the phase transition pressure Pt = 11.5 GPa and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1) structure. Later on, the Poisson’s ratio ν, the ratio RS/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic anisotropy parameter, elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From Poisson’s ratio and the ratio RS/B it is inferred that Hg0.91Mn0.09Te is brittle in nature in both B3 phase and B1 phase. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of Hg0.91Mn0.09Te compounds and still awaits experimental confirmations.

Modeling of the Structural Properties of Hg1–x Cd x Te

Structural properties of Hg1–x Cd x Te are investigated by using first-principles calculations based on density functional theory. An energetically minimized and geometrically optimized model for Hg1–x Cd x Te was formulated. A virtual crystal approximation model for Hg1–x Cd x Te produced a poor fit to experimental lattice parameters and Vegard’s law. However, the virtual crystal approximation model provides reasonably accurate values for the band gap␣energy. An ordered alloy approximation model produced a good fit to Hg1–x Cd x Te lattice parameters and followed Vegard’s law. The ordered alloy approximation also produced a bimodal distribution in Hg-Te and Cd-Te bond lengths in agreement with experimental results.

Measurement of optical and thermal properties of Hg_1−xCd_xTe

Measurements of optical transmission and several thermal properties of Hg(1-x)Cd(x)Te alloys are reported for a few values of the alloy composition parameter x, which was determined by a microprobe technique. The values of the thermal diffusivity, specific heat, and thermal conductivity were measured using the laser-flash method. These results are reported at four discrete temperatures between 90 and 400 K and compared to those of three well-characterized semiconductor materials: Si, InAs, and InSb.

Annealing effects on the microstructural and optical properties of Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers

nand p-type HgxCd1−xTe epilayers have many potential applications, such as infrared detectors, infrared photovoltaic detectors, and infrared focalplane technologies [1–3]. Even though HgxCd1−xTe epitaxial films at high temperatures have been grown by using liquid-phase epitaxy and metalorganic chemical vapor deposition methods for many years [4, 5], interdiffusion or intermixing problems have occurred due to possible cross-doping effect. Recently, p-type HgxCd1−xTe epitaxial films were grown at low temperature by using an in-situ doping process utilizing molecular beam epitaxy [6]. However, high carrier concentrations have not been consistently achieved in p-type HgxCd1−xTe epilayers grown by using in-situ doping [7]. Even though some work concerning the formation of p-type HgxCd1−xTe epilayers through in-situ annealing has been performed [8, 9], ZnTe or ZnSe capping layers were used to avoid surface degradation. Since the growth of capping layers on HgxCd1−xTe epilayers is a complicated process, the formation of p-type HgxCd1−xTe epilayers of high quality and without any capping layer by using in-situ annealing is still necessary. Since the electrical, microstructural, and optical properties of HgxCd1−xTe epilayers significantly affect the quality of high efficiency devices, studies of the physical properties of HgxCd1−xTe epilayers are indispensable when attempting to understand the performance of optoelectric devices based on HgxCd1−xTe epilayers. Furthermore, since thermal treatment is necessary for the fabrication of optoelectronic devices utilizing HgxCd1−xTe epilayers, the role of the thermal annealing is very important in achieving high-performance devices [9]. Therefore, studies of in-situ annealing effects on the electrical, microstructural, optical properties play a very important role in enhancing efficiency. This letter reports the effect of in-situ annealing on the electrical, microstructural, and optical properties of HgxCd1−xTe thin films which were grown by using molecular beam epitaxy (MBE), utilizing CdTe buffer layers on GaAs substrates. The carrier concentration and the mobility of the as-grown and the in-situ annealed Hg0.7Cd0.3Te epilayers were investigated by us-

Properties of Hg1‐xCdxTe epitaxial films grown on (211)CdTe and (211)CdZnTe

AbstractHg1‐xCdxTe (MCT) epitaxial films have been grown employing single crystalline substrates of CdTe and Cd0.96Zn0.04Te with (211)Cd and (211)Te crystalline orientations. The Isothermal Vapor Phase Epitaxy (ISOVPE) technique without Hg overpressure has been used for the epitaxial growth. Substrates and films were characterized by optical microscopy, chemical etching and x ray diffraction (Laue technique). The electrical properties were determined by Hall effect measurements. The characterization results allowed to evaluate the crystalline quality of MCT films. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photo-electronic phenomena in narrow gap Hg1−xCdxTe

Abstract The photo-electronic properties of Hg 1− x Cd x Te grown by molecular beam epitaxy (MBE) or by liquid phase epitaxy (LPE) were investigated using Fourier transform transmission spectroscopy, Fourier transform photoluminescence measurements, spectroscopic ellipsometry (SE), as well as magneto-optics and magnetic-field-dependent Hall studies. The investigation was carried out from liquid helium to room temperatures in the infrared band up to 10 μm. Some important impurities and defects states, including As, Sb, Ag, Fe impurities and Hg vacancy as well as their complexes in Hg 1− x Cd x Te, were carefully studied. We obtained the energy levels of the impurity states and their optical, electric and magnetic behaviors. By SE measurement, a number of very useful parameters, such as the real and the imaginary part of dielectric constant, gap energies corresponding to important critical points, were extracted. Mobility spectra and multi-carrier fitting procedure were used to separate the contributions to the measured mobility from the light holes, heavy holes, and electrons. As a result, the sign change of transverse conductivity component with applied magnetic-field is explained according to multi-carrier process. Hg 1− x Cd x Te (MCT) is one of the most important infrared materials, which is subjected to intensive studies. Its optical and electrical properties are widely used for the fabrication of high performance photoconductive and photovoltaic detectors. Some of characteristics that directly affect device performance, such as impurities, defects, as well as the lifetime of the minority carriers, remain as the major concern. Recently, the quality of the MCT material grown by MBE and LPE has been improved and accurate control over the doping levels for several dopants have been realized [1–3] . Following the progresses made in material preparation and doping, we are able to study the material systematically. In this paper, we report the recent progress made on the investigation of the electrical and optical properties of both doped and undoped MCT in our laboratory using Fourier transform spectroscopy (FTIR), photoluminescence, magneto-photoconductivity, transport measurement, as well as SE.

Electrophysical properties of Hg1−x CdxTe crystals under hydrostatic pressure

Electrophysical properties of Hg1−x CdxTe crystals under hydrostatic pressure

Photoelectric properties of Hg1−x CdxTe single crystals grown from the vapor phase

The electrical and photoelectric properties of Hg0.1Cd0.9Te crystals grown by chemical vapor transport are investigated experimentally. The temperature dependences of the carrier concentration and mobility are determined. The photoelectric properties of these crystals fit a model based on the existence of fast and slow recombination centers.

Electrical properties of Hg1−x MnxTe-based photodiodes

Electrical properties (at 80K) of p-n junctions fabricated by ion milling of p-type Hg0.91Mn0.09Te are analyzed. The forward current-voltage characteristics at low biases is shown to be governed by carrier recombination in the space charge region and at higher biases its voltage dependence is deformed due to the voltage drop across the high-resistance layer in the diode structure. Under reverse bias, carrier tunneling suppresses other transport mechanisms. At higher reverse biases, impact ionization by high-energy carriers is responsible for the additional increase in the diode current.

Effects of Sr substitution on dimensionality and superconducting properties ofHg0.7Pb0.3Ba2Ca2Cu3Oy

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Effect of lattice match and Zn addition on the properties of Hg 1− x(Cd 1− yZn y) xTe epilayers grown by isothermal vapor phase epitaxy

Isothermal vapor phase epitaxy (ISOVPE) growth of Hg 1− x Cd x Te (MCT) and Hg 1− x (Cd 1− y Zn y ) x Te (MCZT) was carried out on the substrates of CdTe and nearly lattice matched Cd 1− y Zn y Te ( y=0.045, CZT) to HgTe, respectively. The properties of MCZT/CZT epilayers with lattice mismatch and Zn addition were characterized and compared with those of MCT/CdTe epilayers. There is no obvious difference in electrical properties between MCT and MCZT epilayers. The hardness of MCZT is significantly greater than that of MCT. This is a good indication of the stability of the MCZT. Full width at half maximum (FWHM) of a four crystal X-ray rocking curves for the lattice matched MCZT/CZT is extremely smaller than that of the MCT/CdTe and the smallest FWHM value 36 arcsec, which is comparable to those reported by the other epitaxial methods.