Properties Of Hg Research Articles

Modification of HgCdTe–Native Oxide Interface by Annealing

The interface properties of Hg 1-x Cd x Te (MCT) with native oxide (NO) after annealing at various stages of MIS device (Me-Si 3 N 4 -SiO 2 -NO-MCT (p-type)) fabrication have been investigated. Heat treatments were provided in vacuum and in the atmosphere at temperatures of 100 to 130 °C before and after native oxide formation and after deposition of SiO 2 overcoated with Si 3 N 4 . The fixed charge value in the oxide varied from -2.5 × 10 11 cm -2 to +5 × 10 11 cm -2 in dependence on the annealing conditions. At the same time the amount of interface traps and near-surface bandgap states changed. It is assumed that these changes are caused by mercury migration at heating. The vacuum annealing of the oxidized samples before deposition of the dielectric layers significantly improves the MCT-insulator interface properties.

Optimization of the structural properties of Hg1−x CdxTe (x = 0.18−0.30) alloys: Growth and modeling

The conditions for the metalorganic molecular beam epitaxial growth of Hg1−xCdxTe (x = 0.18−0.32) alloys at very low growth temperatures (T ≤150°C) have been optimized by correlating the surface properties and crystalline perfection with the incident Hg flux. A window for growth has been defined for x = 0.18, 0.23, and 0.32. A thermodynamic model has been developed to account for void formation. A neural net model has been used for the first time to model the dependence of void density on the Hg flux and the x-ray rocking curve widths on growth parameters. The combination of these two complementary modeling techniques allows for a flexible process optimization to be carried out with a minimum effort spent in calibration runs.

Magnetoluminescence properties of Hg1−xCdxTe epitaxial layers and superlattice structures grown by metalorganic molecular beam epitaxy

We present a study of the electro-optical properties ofHg1- xCdxTe epitaxial layers and Hg1-x CdxTe/CdTe (0.28 < x < 0.30) superlattice structures by x-ray diffraction, lateral transport and photo- and magneto-luminescence measurements. Systematic studies of the excitation intensity and magnetic field dependence of the photoluminescence revealed direct evidence of an excitonic contribution to the observed luminescence in Hg1- xCdxTe epitaxial layers. Similar investigations of the superlattice structures indicated that excitonic corrections were required to adequately fit the luminescence data. Optical gains of 80 cm−1 were obtained for an excitation intensity of 100 kW/cm2 indicating suitable electro-optical properties for making efficient mid-infrared laser diodes.

Transient behavior of Hg1−xCdxTe films deposited on (100) CdTe substrates by chemical vapor transport

The growth history of Hg1−xCdxTe films deposited on (100) CdTe substrates by chemical vapor transport (CVT) has been studied, for the first time, by using a transient growth technique. The observed morphological evolution of Hg1−xCdxTe films deposited at 545°C shows a transition behavior from three-dimensional (3D) islands to two-dimensional (2D) layer growth. The experimental results indicate that the so-called critical time needed for the above morphological transition is about lh under present experimental conditions. Based on the chemical bonding properties of Hg1−xCdxTe, and on the behavior of the morphological transition, the Stranski-Krastanov growth mode is suggested for the epitaxial growth system. The time dependence of the growth thickness, of the growth rate (R100) along the [100] direction, and of the surface composition all reveal a transient behavior. These are related to the nature of the Hg1-xCdxTe/ (100)CdTe heterojunction and to the surface reactions. Comparison of the growth rates and of the total mass deposited as a function of time shows the relationship between epitaxial growth and mass flux of the Hg1−xCdxTe-HgI2 chemical vapor transport system.

Growth and characterization of HgCdTe heterostructures by metalorganic molecular beam epitaxy

HgCdTe continues to be the most important semiconductor material for infrared detector applications. To date issues relating to spatial uniformity and repeatability of alloy composition have hampered the development of this technology. In this paper, we describe the growth and properties of Hg0.72Cd0.28Te epilayers and Hg0.72Cd0.28TeCdTe superlattices grown by metalorganic molecular beam epitaxy. The HgCdTe epilayers exhibited a high degree of lateral and vertical alloy composition homogeneity and also very high run-to-run uniformity. HgCdTeCdTe superlattices were also grown with a variable barrier and constant well thickness. The measured periodicity from X-ray diffraction rocking curves closely agreed with the desired values. Infrared Photoluminescence studies confirmed the high crystallinity and suggested that the luminescence was strongly excitonic with a bound exciton linewidth of 8 meV at 6 K.

Vapor phase epitaxy of Hg 1− xCd xTe on CdTe heteroepitaxial substrates

To grow Hg 1− x Cd x Te layers for infrared (IR) detector fabrication, the new technique of vapor phase epitaxy (VPE) on CdTe heteroepitaxial substrates (HS) has been studied in detail. A theoretical simulation of the VPE growth process has been carried out. Hg 1− x Cd x Te layers were grown by VPE at 530°C in evacuated ampoules. CdTe sapphire and CdTe GaAs HS obtained by metalorganic chemical vapor deposition (MOCVD) technique were employed as substrates. The melt solution of Hg 1− y Te y was used as a VPE source, and the dependence of the VPE growth rate on the source composition in the range y = 0.65−0.85 was studied. Various experimental methods were used to characterize the effect of VPE growth conditions on the properties of Hg 1− x Cd x Te layers like component distribution, surface morphology, structural quality, optical and electrical properties. Our results show a great potential for the VPE on HS technique for the epitaxy of IR grade Hg 1− x Cd x Te.

Effect of preparation on Hg−Ba−Ca−Cu−O superconductors

Some main features of the non-linear synthesis process are described by theoretical considerations. Results of typical preparation methods are compared to each other and to those obtained by the experiments designed specially for the study of the effect of synthesis on the superconducting properties of Hg−Ba−Ca−Cu−O compounds. As is shown, the controlled Hg-vapour pressure method, the sealed tube with phase formation procedure, the high-pressure synthesis and the freeze-drying method seem to be unambiguously reliable to provide high-quality samples. Significant deviations from these fundamental synthesis routes can lead to significant deviations of superconducting parameters.

Bridgman growth and properties of Hg 1− xMn xTe single crystals

A modified Bridgman method with a high temperature gradient was used to grow Hg 1− x Mn x Te single crystals from Te-rich solution. Magnetic susceptibility experiments were performed in the temperature range from 80 to 300 K. Raman scattering measurements, carried out at room temperature, revealed two peaks characteristic of the pure HgTe spectrum at 118 cm −1 and 138 cm −1 and a third weaker peak at 256 cm −1.

The performance of Hg1−x Zn x Te photodiodes

This paper considers the Hg1−x Zn x Te alloy system as a potential material for the fabrication of infrared photodiodes. The influence of different junction current components (diffusion, tunneling and depletion layer currents) on the R 0 A product of n+-pHg1−x Zn x Te photodiodes is analysed. The upper theoretical limits of the R 0 A product and detectivity are determined. Results of calculations are compared with experimental data reported by other authors and those measured in our laboratory. Preliminary results on related technology and the properties of Hg1−x Zn x Te prepared by the ion-etching technique are presented.

Annealing effects on the electrical properties of Hg1−xCdxTe grown by two different techniques

Annealing effects on the electrical properties of Hg1−xCdxTe grown by two different techniques

New achievements in Hg1−xCdxTe grown by molecular-beam epitaxy

A review of our recent achievements in the growth of Hg1−xCdxTe by molecular-beam epitaxy is presented here. The influences of the substrate temperature, the crystallographic orientation, and the nature of the substrate on the properties of Hg1−xCdxTe are discussed in detail. We show that to grow high-quality material with good uniformity in terms of the alloy composition and the doping by crystal stoichiometry deviation, the substrate temperature should be between 180 °C and Tmax. We report mobilities as high as 5.0×1205 cm2 V−1 s−1 for n-type layers and 1.2×103 cm2 V−1 s−1 for p-type layers, achieved by precisely controlling the growth parameters. We illustrate that the Hg condensation coefficient is influenced by the crystallographic orientation. Our results show that for Hg1−xCdxTe grown on both the (111)B and the (100) faces of CdTe or GaAs the Hall mobilities are very high and comparable. We report our important achievement of the successful growth of 2-in.-diam Hg1−xCdxTe films on GaAs(100), with Δx/x̄ as low as 0.7% for x̄=0.218 (Δx is the standard deviation and x̄ is the mean value), Δt/t̄ as low as 0.6% for the layer thickness, excellent uniformity in the doping, an high electron or hole mobility. This illustrates the excellent control that our group has achieved toward the growth of this material by molecular-beam epitaxy.

Properties of Hg1−x Cd x Te single crystals grown by THM

Properties of Hg1−x Cd x Te single crystals grown by THM

The Burstein-Moss shift for mercury cadmium telluride

In a heavily doped semiconductor the optical band gap increases due to the Pauli principle. In this paper the properties of Hg0.8Cd0.2Te are discussed using Thomas-Fermi theory which is shown to be appropriate. An expression for the Burstein-Moss shift is derived and related to the position of the transmission edge. The width of the transmission edge is shown to be a function of temperature, doping and variations in the local x-composition. Experimental results are presented to support the results of these calculations.

Properties of Hg1−xZnxTe grown by liquid-phase epitaxy

Epilayers of Hg1−xZnxTe 0.16≤x≤0.26, were grown by liquid-phase epitaxy on CdTe and nearly lattice matched Cd0.76Zn0.2Te substrates. The crystalline, electrical, and optical properties of the epilayers are described. Significant improvement of the epilayer surface morphology and crystallinity was achieved by lattice matching with the substrate. The temperature and composition dependence of the energy band gap in the spectral range relevant to IR photodetection was determined.

Growth and properties of Hg1−xCdxTe on GaAs substrates by organometallic vapor-phase epitaxy

Growth of epitaxial mercury cadmium telluride (Hg1−xCdxTe) on (100) GaAs substrates by organometallic vapor-phase epitaxy is described. Transport measurements made on these layers at 80 K indicate an electron mobility greater than 2×105 cm2/ V s for layers of composition x≂0.2. An intervening CdTe buffer layer was used to accommodate the large (14%) lattice mismatch between these systems, and HgCdTe layers have been grown with CdTe buffer layer thicknesses from 1000 Å to 3 μm. It is shown that a CdTe buffer layer of 2–3 μm is necessary to accommodate the misfit dislocations at the CdTe-GaAs interface.

The behavior of doped Hg 1− xCd xTe epitaxial layers grown from Hg-rich melts

The properties of Hg 1- x Cd x Te epitaxial layers grown from doped Hg-rich melts are examined. Selected dopants were added to large (∽2.5 kg) Hg-rich melts from which liquid phase epitaxial (LPE) layers were grown on <111 >-oriented single crystals of CdTe via ramped vertical dipping. The layers were characterized for impurity concentration distributions by Hall effect measurements and by secondary ion mass spectroscopy (SIMS). Segregation coefficients, carrier types, activities, and activation energies were also measured for many of the dopants. A table which summarizes the significant results is presented. The most promising dopants for this melt system are indium for n-type layers, and arsenic or antimony for p-type layers. Functioning infrared focal plane arrays have been fabricated on double-layer heterostructures grown from doped Hg-rich melts.

Nondestructive analysis of Hg1−xCdxTe (x=0.00, 0.20, 0.29, and 1.00) by spectroscopic ellipsometry. II. Substrate, oxide, and interface properties

Properties of Hg1−x CdxTe substrates, their electrochemically grown anodic oxides, and their interfaces are studied under as-grown conditions using the nondestructive analytic capabilities of spectroscopic ellipsometry to avoid ambiguities arising from destructive analytic techniques. Pseudodielectric functions that are the most accurate representations of the intrinsic bulk responses that we are able to achieve are given for each of the materials studied. The dielectric functions of the oxides are calculated from (tan ψ, cos Δ) data in a three-phase model. These oxides are uniform with sharp interfaces at both substrate and ambient. Residual Te layers of thicknesses of the order of 6%–8% of the initial oxide thicknesses are found on the Hg-containing substrates after their native oxides are stripped with HCl. Four-phase model calculations show that these Te layers are not present (±2 Å) in the as-grown condition for the Hg-containing materials and therefore cannot be invoked to explain leakage in integrated-circuit devices. However, a small residual amorphous (a-Te) layer ∼1.5 Å thick between the semiconductor and electrochemically grown anodic oxide is seen for CdTe. The optical data show the oxide on CdTe to be predominantly the tellurite CdTeO3. The composition of the oxide on HgTe cannot be identified uniquely, but it probably contains a substantial fraction of TeO2. A residual absorption tail below the fundamental edge on all oxides is consistent with the presence of ∼3%–4% a-Te in the oxides. The oxides on the alloys can be represented as physical mixtures of those of the endpoints, suggesting an oxidation mechanism and a structure consisting of TeO2 and some Hg tellurites captured in a relatively insoluble matrix of CdTeO3. After correcting for residual Te overlayers, all substrate dielectric functions for a given material are found to be identical to within 1% regardless of sample history, placing upper limits of less than 2% for cationic or anionic outdiffusion in these materials. A similar consistency of broadening parameters implies that the actual limits may be much lower. The properties of the Hg1−x CdxTe compounds studied in this work vary smoothly with x and show no chemical or physical anomalies.

Properties of Hg0.71Cd0.29Te and some native oxides by spectroscopic ellipsometry

We have used spectroscopic ellipsometry to determine the complex dielectric function from 1.5 to 6.0 eV for Hg0.71Cd0.29Te and some of its native oxides. The electrochemically grown anodic oxide was found to have an absorption threshold near 3 eV and its dielectric function shows some of the features of TeO2. We found no evidence for a Te-rich layer between the native oxide and the semiconductor. However, after stripping the oxide with HCl, a residual layer with Te-like optical and chemical properties did appear. Thin native oxides formed by exposure to ozone-containing oxygen had dielectric functions similar to that of the anodic oxide but with a broader absorption edge. These oxides could be stripped partly by water and totally by HCl. This confirms that they are a mixture of several oxides as also concluded in other investigations. We found no evidence for any disorder or defects induced in HgCdTe by anodization or etching.

Properties of Hg‐ and Cd‐Spores of Bacillus megaterium QM B1551

Hg- and Cd-spores of Bacillus megaterium QM B1551 were produced in Schaeffer's medium containing mercuric chloride and cadmium chloride respectively. Metals were added to the medium at 9 hr of incubation (Stage V) to give a final concentration of 50 microM. It was found by electron microscopic and biochemical studies that the coats of both Hg- and Cd-spores were thinner than those of control spores. Of the total Hg and Cd in the spores, 77% of the Hg and 63% of the Cd were detected in the spore coats. Hg- and Cd-spores were less resistant to heat and more sensitive to germinants than control spores. Other properties of Hg- and Cd-spores were similar to those of control spores. These results suggest that the spore coat has some relationship to the heat resistance and germinability of spores.

Resonant states and their influence on optical properties of Hg1-xCdxTe type crystals

A three-band Koster-Slater model is applied to resonant states induced by a highly localised potential in a Hg1-xCdxTe type band structure. The density of states is obtained as a function of four parameters; resonant or discrete states can appear in various energy regions. The statistics of these states is discussed as well as their influence on optical transitions (interband and intraband) for various positions of the Fermi level. Characteristic dips, peaks and thresholds appear in the absorption spectrum.