Te Samples Research Articles

DX Centers in AlGaAs and Pressurised GaAs

ABSTRACTIn this paper, we present results of our investigations on some aspects of the DX centers. It is shown from the low temperature Hall mobility measurements that the charge state of the DX center is neutral supporting the positive U model for the DX center. Hall and DLTS measurements on Al-rich Al0.8Ga0.2As:Te sample show a reversal in the ordering of the energies of the hydrogenic and deep states of the Te donor, with the DX state lying higher than the X valley related effective mass state. Thermal emission properties of the pressure induced DX states of Ge and Se donors in neutron transmutation doped (NTD) GaAs are discussed.

Room temperature, local tailoring of electronic properties of Hg0.3Cd0.7Te by applying an external electric field

Electronic properties of initially homogeneous (Hg,Cd)Te samples have been modified on a local scale, in a stable manner at room temperature, by reverse biasing of small-area Schottky contacts on them. This was shown, after the bias voltage had been lifted, by current-voltage measurements and by electron beam-induced current scans. The creation of a clear diodelike structure in the vicinity of the Schottky contact on a scale of about hundred μm could be explained by electromigration of electrically active ions and/or by generation of point and line defects. The latter type of defect was revealed by chemical etch after application of the field.

Magnetic Susceptibility of PbSnMnTe in the Transition Region between Ferromagnetic and Spin Glass Phase

The ac magnetic susceptibility (χ) was measured in the temperature range T = (1.5+50) K for Pb1- x - y Sn y Mn x Te samples with a composition y = 0.72, x = 0.015+0.04 and carrier concentrations in the range p = (2.85+14) x 10 20 cm -3 . The breakdown of ferromagnetism and the formation of a spin glass phase are observed with an increasing carrier concentration. It is experimentally evidenced as continuous deviation of χ(T) from the characteristic critical behavior observed for ferromagnetic samples.

Observation of a deep level in p-type Hg0.78Cd0.22Te with high dislocation density

To investigate the possibility that deep levels are associated with dislocations in narrow band gap HgCdTe, deep level transient spectroscopy has been used to study n+-p diodes fabricated on p-type bulk Hg0.78Cd0.22Te samples with either a ‘‘normal’’ dislocation density of about 105 cm−2 or a high dislocation density of about 106 cm−2. These samples which are gold doped with a hole concentration of 1.2×1015 cm−3, have a band gap of about 0.12 eV at 77 K. In samples with a ‘‘normal’’ dislocation density, a deep level of about 80 meV above the valence band was found. However, a midgap level of about 60 meV above the valence band with larger peak amplitude and broader line shapes was found in the sample with a high dislocation density.

Exchange interaction in rare-earth-doped IV-VI diluted magnetic semiconductors.

The magnetization and magnetic susceptibility of Bridgman-grown ${\mathrm{Sn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te samples with values of x up to 0.09 have been measured in fields up to 5.5 T over a temperature range from 2 to 300 K and in fields up to 23 T at 4.2 K. The low-field, high-temperature susceptibility data followed the Curie-Weiss relation with a small Curie temperature. The magnetic-field dependence of the magnetization was fitted to an expression containing a Brillouin function, representing isolated magnetic ions, plus a term representing pair interactions. Both the susceptibility and the high-field magnetization data indicated a weak antiferromagnetic coupling among Gd ions. These results are compared with our previously obtained exchange parameters for ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te and ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Eu}}_{\mathit{x}}$Te. The exchange interaction in ${\mathrm{Sn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te is larger than in PbTe-based, rare-earth-doped chalcogenides, in agreement with the smaller cation-anion spacing in SnTe-based compounds. A ferromagnetic or spin-glass ordering due to the possible Ruderman-Kittel-Kasuya-Yosida interaction in ${\mathrm{Sn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te with high hole concentration was not observed.

Room Temperature Local Tailoring of Electronic Properties of Hg1-xCdxTe by Application of an External Electric Field

ABSTRACTElectronic properties of originally homogeneous samples of (Hg, Cd)Te, CuInSe2 and (CuAg)InSe2 have been modified on a local scale, in a stable manner, at room temperature, by reverse biasing of small area Schottky contacts on them. This is shown, after the bias voltage is lifted, by I-V measurements and by Electron Beam Induced Current scans. The creation of a clear diode-like, and, in the case of (CuAg)InSe2, transistor-like structure, in the vicinity of the Schottky contact, on a scale of about hundred um, could be explained by electromigration of electrically active ions and by the simultaneous generation of point and line defects. The latter type of defects is revealed for (Hg,Cd)Te by chemical etch, after application of the field.

Comparative optical studies of semimagnetic II–VI quantum well structures

MBE grown semimagnetic quantum well structures CdTe (Cd,Mn)Te on InSb, ZnTe (Zn,Mn)Te on GaSb, and ZnSe (Zn,Mn)Se on GaAs are studied by optical spectroscopy. Confinement and lattice misfit induced strain effects on the optical spectra, especially the lh-hh well exciton splitting, are discussed. In contrast to CdTe (Cd,Mn)Te , internal Mn 2+(3d 5) transitions are observed in ZnTe (Zn,Mn)Te and ZnSe (Zn,Mn)Se samples due to the increased band gap. The valence band offset is found to be of the same order of magnitude in the three investigated systems.

PAC and XPS studies of II–VI compounds

The perturbed angular correlation (PAC) method has considerable potential for studying near-surface defects of materials on a microscopic scale, especially in combination with standard surface techniques. We have characterized the near-surface and surface regions of II–VI compounds using PAC and X-ray photoelectron spectroscopy (XPS). PAC was used to identify point defect complexes containing the radioactive 111In probe atoms, which were diffused into Cd 0.96Zn 0.04Te, Cd 0.8Mn 0.2Te and Hg 0.79Cd 0.21Te (MCT) samples under vacuum from 200 to 550 °C. After the Cd(Zn)Te samples were annealed at 450 °C for 30 min, 60% of the In atoms occupied unique non-cubic sites, characterized by an interaction frequency ν Q = 60 MHz and an asymmetry parameter η=0.2. These sites were attributed to In-(cadmium vacancy) complexes, since this signal was eliminated by subsequent annealing in a cadmium atmosphere. Similar results were obtained for the Cd(Mn)Te samples, but the vacancy complex occured at a lower annealing temperature. The XPS data for Cd(Mn)Te showed that its oxide characteristics differed considerably from those of CdTe. Although oxide formation of CdTe occurs very slowly after sputter cleaning, a significant TeO layer was formed on the Cd(Mn)Te surfaces after only 10 min exposure to air. In addition, deionized water removed the native oxide completely for CdTe but not for Cd(Mn)Te. For MCT, annealing at 350 °C caused the formation of two defect complexes, characterized by frequencies of 83 and 92 MHz, and η ≈ 0.1. These PAC signals vanished after annealing under a mercury atmosphere, indicating that they were also due to In-vacancy complexes.

Deformation behavior of CdTe and (Cd, Zn)Te single crystals between 200 and 600 °C

The deformation behavior of CdTe and (Cd,Zn)Te single crystals oriented for single slip has been investigated in the temperature range 200–600 °C. The addition of 4.5 at.% Zn increases the yield strength by about eight times over that of CdTe crystals. Further, in both cases the yield strengths are nearly temperature independent above 300 °C. Arguments have been developed to rationalize these observations. Deformed structures have been evaluated by transmission electron microscopy. Parallel sets of dislocations, dislocation dipoles, loops, tangles and networks are observed in the deformed samples. In addition, the (Cd,Zn)Te samples deformed at 200 °C show profuse twinning. The evolution of the deformed structures has been discussed in the light of earlier studies pertaining to the elemental and III–V compound semiconductors. Also, the formation of twins is rationalized.

Magneto-optical properties of the DX centre in Al0.35Ga0.65As:Te

Magneto-optical absorption spectra of a 0.4 mm thick, single-crystal Al0.35Ga0.65As:Te sample give evidence for two bleachable absorbers, one of which is identified as the DX centre. The bleached-state absorption coefficient and magnetic circular dichroism (MCD), measured from 0.66 to 2.2 mu m at 1.7 K, are adequately described by the Drude free-electron model, in terms of which a value for the electron effective mass is obtained. Cooling the sample in darkness leads to transmission transients, from which the absorption coefficient and optical-conversion cross section for the bleachable deep DX ground state are derived. The MCD at the beginning of each transient is identified also with the DX ground state, and its temperature dependence reveals that the bulk of it has a non-paramagnetic origin. The authors conclude that the paramagnetic contribution to the MCD from the DX ground state is very small, being less than 0.004% of its peak absorption coefficient. This provides strong support to the diamagnetic ground-state, negative-U model of Chadi and Chang (1988, 1989). The origin of the second bleachable absorber (threshold approximately 1.6 eV) has not been established.

Photoluminescence in ZnSe:Te Prepared by Solution Growth

ZnSe:Te crystals with different Te concentrations were grown from solution using Sb2Se3-Sb2Te3 and Se-Te as solvents, and their photoluminescence properties were investigated. The emission in the ZnSe:Te samples was composed of three bands located at 2.70 eV (TA), 2.50 eV (TB) and 2.35 eV (TC), the relative intensities of which depended on the sample temperature. The energy position of all three bands was independent of the Te concentration. For the Te concentrations of 0.02%, 1.96% and 9.4%, the dominant band was the TA band, the TB band and the TC band, respectively. We attributed the TA band to the emission of excitons bound to the nearest-neighbor Te-Te pairs (Te2). The TB band was tentatively attributed to excitons bound to the Te3 centers, and the TC band to the Ten centers (n≥3).

Neue A4B3-Moleküle: P3SbS3, P4S2Te und P4STe2 / New A4B3 Molecules: P3SbS3, P4S2Te and P4STe2

The new molecules P3SbS3, P4S2Te und P4STe2 were extracted with CS2 from mixtures of S. Sb and P4S3, and P, S and Te samples respectively, which were previously molten and then annealed for several days. In the P3SbS3 molecules the apical phosphorus position of P4S3 is substituted by antimony. In the molecules P4STe2 and P4S2Te one or two of the sulphur bridges are substituted by tellurium. X-ray and 31P NMR data of the compounds are given.

Band structure parameters of Pb0.25Sn0.72Mn0.03Te semimagnetic semiconductors

Reflectivity spectra of Pb0.25Sn0.72Mn0.03Te samples were measured in the region of the plasma edge. The p-type samples with very high carrier concentrations (pH=2.2*1020-1.2*1021 cm-3) were studied at T=77 K. On the basis of the free-carrier dispersion theory, the experimental values of the susceptibility effective mass, the optical dielectric constant and the optical mobility were determined. Strong carrier concentration dependence of the plasma frequency and the hole effective mass was observed. The analysis of these dependences was made on the basis of a two-valence-band model. The parameters of the model, the energy gap, the effective mass of heavy holes and the energy separation between light- and heavy-hole-band edges, are determined and discussed.

119Sn-Emission Mössbauer Studies on 119mTe and 119Sb in S, Se, and Te

Abstract The valence states of 119Sn produced by the EC decay of diluted 119Sb and 119mTe chemically doped in S, Se, and Te were studied by emission Mössbauer spectroscopy. The Mössbauer spectra of S(119mTe) and Se(119mTe) consist of peaks ascribable to Sn(IV) and to Sn(II) surrounded by S or Se, respectively. The Mössbauer spectra of Te(119Sb) samples show that, though a greater part of the 119Sb atoms are dispersed in the Te matrix after coprecipitation and sublimation, upon slow recrystallization after fusion most of the dispersed 119Sb atoms aggregate to form microcrystals of 119Sb2Te3.

Non-classical conductivity in a bulk semiconductor up to 35 K

We observed non-classical contributions to the conductivity in three-dimensional samples at temperatures up to 35 K. The experiments were carried out inn-type Hg0.8Cd0.2Te samples having dimensions as large as 8 ×28×25 μm3. The two resistivity contributions, i.e. the ‘normal’ metallic behaviourρ0 and a partΔρ provided by electron interference, are separated using a method disturbing the additional contribution by heating the electrons in electrical fields. The observed temperature and electric field dependence are compared with existing theories.

Photoplastic effects in Cd0.2Hg0.8Te

We irradiated Cd0.2Hg0.8Te samples at room temperature in the plastic range, with a CO2 laser beam the wavelength of which (λ=10 500 nm) is 20% longer than the absorption threshold. We observed a positive photoplastic effect (PPE) of the order ΔσPPE/σ≈4 to 5%.

Free-carrier absorption due to collective and one-particle processes in a linear conduction band

A quantum mechanical theory of free-carrier absorption in semiconductors with a nonparabolic conduction band is developed. The absorption due to scattering on ionized impurities is considered in zero-gap Cd x Hg 1− x Te taking into account both single particle and collective excitations. Because of the lack of the plasmon damping for the linear conduction band, the contribution to the absorption coefficient related to the free-carrier plasmon generation extends over a wide spectral region. It is shown that the strong angular dependence of the optical matrix element as well as of the electron-impurity scattering amplitude lead to significant reduction of the total absorption coefficient with respect to a typical wide-gap semiconductor. The infrared measurements taken on a few highly doped, n-type Cd x Hg 1− x Te samples with a composition close to x = 0.2 confirmed the theoretical predictions.

Photoplastic effects in Cd0.2Hg0.8Te

We irradiated Cd0.2Hg0.8Te samples at room temperature in the plastic range, with a CO2 laser beam the wavelength of which (λ=10 500 nm) is 20% longer than the absorption threshold. We observed a positive photoplastic effect (PPE) of the order ΔσPPE/σ≈4 to 5%.

Depth profiling of element concentration using low energy proton induced X-ray emission

A nondestructive method for the profiling of near-surface compositional changes in compound materials is described. It is based on measurements of the particle-induced X-ray emission (PIXE) yields of the constituents of the sample at ever decreasing projectile energies. By performing PIXE measurements at different (low) energies, and fitting the measured yields by an iterative program which changes the depth distribution of the elements until the desired agreement with the measured yields is reached, the elemental concentration as a function of depth is obtained. The use of the technique is demonstrated for the case of a Hg 1− x Cd x Te ( x = 0.21) sample in which gradual Hg loss has been induced in the first 3000 Å by heat treatment. PIXE measurements were performed with protons at 7 different energies from 340 to 80 keV. When the results of these measurements are fed into the computer program the Hg profile is very well reproduced, as inferred from the excellent agreement with the results of heavy ion (20 MeV C +4) RBS measurements.

A Rb-Sr age of glassy material from a lunar meteorite and its origin on the moon

The impact of a planetesimal with a planet produces craters. Part ia l or complete melting may be induced on and around the collision spot. Chronological studies of these re-melted samples should give us the ages of the impacts and informat ion about crater format ion on planets and satellites. Here we report for the first time a 87Rb87Sr study on an impact-melted sample (Yamato-82192 SubNo.63B), one of the lunar meteorites, the moon rocks having been unexpectedly recovered on the earth. The chip, Y-82192 SubNo.63B, was collected near the Yamato Mountains, Antarct ica [1]. The lunar meteorites, including Y-82192, are considered to have derived from lunar highland, based on the petrological and chemical studies [2, 3]. The chip, Y-82192 SubNo.63B, shows a glassy feature distinct from other lunar meteori te samples characterized as anorthosi te breccia. This glassy l i thology is considered to be produced by impact melting. A small part (5 mg) of the sample was used for analysis on a whole rock sample, other parts ( ~ 60 mg) were crushed and separated into several fractions with heavy liquids (methylene iodide and bromoform), and Rb-Sr analyses were performed on each fraction. (The fraction suspended in acetone is called "suspension" here). Sr isotope ratios were measured with a VG 354 mass spectrometer and the abundances of Sr and Rb were analyzed by the isotope dilut ion method, using a mass spectrometer (JEOL JMS-05RB). The results are shown in Table 1. The errors for abundances are within 0.5 %. Based on the analyses of the major element compositions by E P M A (JEOL JXA-733), the fractions with densities lower than 3.25 g cm -3 are composed chiefly of Ca-rich plagioclase or Ca,Al-r ich glass. The fraction with the highest density (higher than 3.25 g cm -3) is composed of olivine with a small amount of pyroxene. As reported previously [3], the REE abundances in this melted sample remained unchanged irrespective of melting. On the other hand, as shown in Fig. 1, the Rb-Sr system was significantly disturbed by the melting event, although the whole rock sample of Y82192, SubNo.63B, lies near a 3.95 x 109a line defined by other lunar meteorites (see solid line in Fig. 1 ; the da ta of the solid line are from [3]). Among the separated fractions plus the whole rock under consideration, five (four fractions with densities lower than 3.25 and the whole rock sample) fall nearly on a line and the other two fractions (suspension and a fraction with density higher than 3.25) lie at distinct positions. Concerning the high melting tem-