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Showing papers by "Solid State Physics Laboratory published in 1996"


Journal ArticleDOI
TL;DR: In this article, the electronic structure of the perovskite LaCoO 3$ for different spin states of Co ions was calculated in the local density approximation LDA+U approach.
Abstract: The electronic structure of the perovskite ${\mathrm{LaCoO}}_{3}$ for different spin states of Co ions was calculated in the local-density approximation LDA+U approach The ground state is found to be a nonmagnetic insulator with Co ions in a low-spin state Somewhat higher in energy, we find two intermediate-spin states followed by a high-spin state at significantly higher energy The calculations show that Co 3d states of ${\mathit{t}}_{2\mathit{g}}$ symmetry form narrow bands which could easily localize, while ${\mathit{e}}_{\mathit{g}}$ orbitals, due to their strong hybridization with the oxygen 2p states, form a broad \ensuremath{\sigma}* band With temperature variation which is simulated by a corresponding change of the lattice parameters, a transition from the low- to intermediate-spin state occurs This intermediate-spin (occupation ${\mathit{t}}_{2\mathit{g}}^{5}$${\mathit{e}}_{\mathit{g}}^{1}$) can develop an orbital ordering which can account for the nonmetallic nature of ${\mathrm{LaCoO}}_{3}$ at 90 KT500 K Possible explanations of the magnetic behavior and gradual insulator-metal transition are suggested \textcopyright{} 1996 The American Physical Society

641 citations


Journal ArticleDOI
TL;DR: Qualitative arguments and numerical estimates show that this mechanism may be important in the inorganic spin-Peierls compound CuGeO3 and can make the 90 degrees superexchange of half-filled shells antiferromagnetic.
Abstract: A mechanism is suggested which can modify in certain cases the Goodenough-Kanamori-Anderson rules determining the character of superexchange in magnetic insulators; namely, side groups coupled to ligands, which are often present but are usually ignored, may contribute significantly, and may in certain cases even lead to a change in sign of the superexchange interaction. Thus this factor can make the 90\ifmmode^\circ\else\textdegree\fi{} superexchange of half-filled shells antiferromagnetic, in contrast to the usual case. Qualitative arguments and numerical estimates show that this mechanism may be important in the inorganic spin-Peierls compound ${\mathrm{CuGeO}}_{3}$. \textcopyright{} 1996 The American Physical Society.

140 citations


Journal ArticleDOI
TL;DR: In this paper, the occurrence of polyanions in a group of liquid ionic alloys, viz. alloys of the alkali metals with 13, 14, 15 and 16 elements (post-transition-metal groups 3, 4, 5 and 6), is discussed.
Abstract: The occurrence of polyanions in a group of liquid ionic alloys, viz. alloys of the alkali metals with 13, 14, 15 and 16 elements (post-transition-metal groups 3, 4, 5 and 6), is discussed. It is shown that there are strong parallels with the corrresponding crystalline phases, in which polyanions such as .Pb4/4 , .Sb /1 and .Te2/2 exist, known for a long time as 'Zintl ions'. Little evidence exists for remnants of the diamond-lattice-type Zintl ion in liquid alkali-group-13 alloys, but in the alloys of Tl with K, Rb and Cs very long-range superstructures have been found, which are related to the occurrence of large, compact, polyhedral clusters in many crystalline phases. A stability rule, first proposed by Geertsma, relating the stability of the polyanions to the size of the cations, is universally observed. Furthermore it is shown that the range of the superstructure in the liquid is with remarkable precision proportional to the intercluster distance in the corresponding solids. The interpretation of the experimental data in terms of polyanion formation is discussed critically. There remains a paradox. Some sharp experimental features (superstructure peaks and maxima in the resistivities and stability functions) seem to indicate that the Zintl ions in the liquid are near perfect whereas specific heat results and ab initio computer simulations clearly show that the structure of the liquid is seriously blurred.

87 citations


Journal ArticleDOI
TL;DR: In this paper, a general analytical relation between the inverse of zero-bias resistance -area product and the perimeter-to-area ratio of the diodes in variable-area diode array test structures currently used in HgCdTe technology is presented.
Abstract: This paper is an attempt towards presenting a general analytical relation between the inverse of zero-bias resistance - area product and the perimeter-to-area ratio of the diodes in variable-area diode array test structures currently used in HgCdTe technology Contributions from (i) surface leakage currents due to band bending at the HgCdTe surface (ie the HgCdTe - passivant interface), (ii) surface generation currents in the depletion region in the immediate proximity of the HgCdTe - passivant interface, (iii) surface leakage currents due to Zener tunnelling, (iv) leakage currents due to an imperfect HgCdTe epilayer - substrate interface and (v) bulk currents have all been taken into consideration in arriving at the relationship between the inverse of zero-bias resistance - area product and the perimeter-to-area (p/A) ratio of the diodes The derived relation predicts in general a nonlinear behaviour of the data It is shown by the detailed discussions that the general relation can be of great practical help in identifying the various possible mechanisms contributing to the surface leakage currents Use of constant perimeter and variable-area (CPVA) test structures along with the usual variable perimeter and area (VPA) test structures to interpret the linear data, and additional experiments to distinguish the surface Zener tunnelling and surface generation - recombination mechanisms have been proposed The previously reported data on variable-area test structures have been shown to fit very well with the presented model

26 citations


Journal ArticleDOI
TL;DR: The experimental results of multiphoton electron emission from Cu and W induced by 2-eV 100-fs laser pulses with s and p polarizations at incidence angles between 0 degrees and 85 degrees and different intensities show a third-order nonlinear photoemission process for Cu and a fourth-order behavior for W.
Abstract: The experimental results of multiphoton electron emission from Cu and W induced by 2-eV 100-fs laser pulses with $s$ and $p$ polarizations at incidence angles between 0\ifmmode^\circ\else\textdegree\fi{} and 85\ifmmode^\circ\else\textdegree\fi{} and different intensities are reported. The data show a third-order nonlinear photoemission process for Cu and a fourth-order behavior for W. For both metals the electron emission is higher for the polarization in the incidence plane, with a maximum value at the pseudo-Brewster angle, while the electron yield as a function of the incidence angle exhibits an unambiguous dependence on the bulk absorption coefficient and it can be accounted for on the basis of the Fresnel equations.

25 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of infrared phototransistors based on a quantum well and a quantum-wire structure, utilizing intersubband electron transitions, were compared. And it was shown that the quantum-wired infrared phototonics can surpass the infrared photosistors with a quantumwell in performance especially at low temperatures.
Abstract: Infrared phototransistors based respectively on a quantum-well and a quantum-wire structures, utilizing intersubband electron transitions, are considered using developed analytical model. The dark currents and responsivities of the phototransistors in question are compared. It is shown that the quantum-wire infrared phototransistor can surpass the infrared phototransistor with a quantum well in performance especially at low temperatures. This is due to the one-dimensional nature of the electrons in the quantum-wires providing higher energy of thermal excitation, leading to low dark current and sensitivity to normal incident radiation.

21 citations


Journal ArticleDOI
TL;DR: In this paper, electrical and photoluminescence measurements were carried out on doped n-CdTe and were found to be passivated at about 150°C and 50% at 170°C, respectively.
Abstract: Passivation effects in In doped n-CdTe upon exposure to rf hydrogen plasma are studied by electrical and photoluminescence measurements and were found to be maximum at about 150°C. Depth profiling by capacitance-voltage measurements show passivation of approximately an order of magnitude at 150°C and 50% at 170°C. No visual surface damage is seen. Reverse bias annealing experiments show that atomic hydrogen drifts in a charged state in n-CdTe, with reactivation kinetics of the donors different from the other well studied semiconductors. Manifestation of the donor passivation in photoluminescence is seen by the reduction of the donor bound luminescence.

20 citations


Journal ArticleDOI
TL;DR: In this article, a novel infrared photodetector based on a multiple quantum dot structure is considered theoretically, and an analytical model of the device is developed to evaluate its performance.
Abstract: A novel infrared photodetector — the quantum-dot infrared phototransistor — based on a multiple quantum dot structure is considered theoretically. An analytical model of the device is developed to evaluate its performance. The dark current and sensitivity are calculated. It is shown that the quantum-dot infrared phototransistor performance can surpass that of the quantum-well photodetectors.

13 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the development of stored energy in pure and doped NaCl samples as well as natural rock salt during irradiation, and the dependencies of the stored energy value on the irradiation temperature and the presence of dopants have been studied.
Abstract: In this paper we describe the development of stored energy in pure and doped NaCl samples as well as natural rock salt during irradiation. The dependencies of the stored energy value on the irradiation temperature and the presence of dopants have been studied. Irradiation experiments at controlled temperatures between 50 and 150°C and doses up to 150 Grad have been carried out. For pure NaCl we have found that the damage is formed only in a relatively narrow range of irradiation temperatures. In almost all cases the effect of doping is that the stored energy value is larger and the temperature range where stored energy develops is wider as compared to pure NaCl.

12 citations


Journal ArticleDOI
TL;DR: In this article, the effect of fixed surface charge density on the performance of HgCdTe (MCT) photoconductive detectors is presented. And the authors show that the accumulation layer improves by a factor of 1.5.
Abstract: The effect of fixed surface charge density on the performance of HgCdTe (MCT) photoconductive detectors is presented in this study. The figure of merit such as the specific detectivity of photoconductive detectors operating at 77 K is calculated with 300 K background and field of view (FOV). The equations leading to the above calculations are developed for the case of a one-dimensional model. Our calculations show that: (i) shows maxima with varying ; (ii) improvement in due to accumulation is observed for values of up to for materials with low as well as high bulk minority carrier lifetimes ; and (iii) is limited by shunt resistance due to passivants having for low- materials. Furthermore, is found to degrade by an order of magnitude from its peak value with increase in from to in a material having ns, whereas no such degradation in is seen for the same range of in a material having . In addition, our calculations predict that the accumulation layer improves by a factor of 1.5 for surfaces having an initial surface recombination velocity as high as .

12 citations


Journal ArticleDOI
TL;DR: In this article, the radiolysis processes in NaCl have been investigated extensively and from these investigations, the authors have obtained a rather clear picture of the radio-lysis process in these model materials and have observed colloids showing Curie paramagnetism, a Curie-Pauli cross-over and normal Pauli behavior.

Journal ArticleDOI
TL;DR: In this article, a new method has been given in this paper which does not require the knowledge of mobility data and the profile generated by this method is compared with the profile obtained with the help of spreading resistance probe and the two profiles agree very well within the experimental error.

Journal ArticleDOI
TL;DR: In this article, first-principles molecular dynamics simulations of the liquid Mg-Bi system at different compositions were presented for the pure Mg and Bi liquid components, the stoichiometric liquid, and a Mgrich composition.
Abstract: The liquid Mg - Bi system exhibits strong compound formation at the `octet' composition . We present results of first-principles molecular dynamics simulations of this alloy system at different compositions: the pure Mg and Bi liquid components, the stoichiometric liquid, and a Mg-rich composition . For the pure liquids, our results are in excellent agreement with experimental diffraction data. For , a significant modification of the characteristics of the local ordering is found w.r.t. the crystalline -phase: the ordering in the liquid is much more ionic. This structural modification is consistent with the structure of the superionic -phase, that was reported recently by Barnes et al 1994 J. Phys.: Condens. Matter 6 L467. Our simulations cannot reproduce the `reverse' metal - nonmetal transition observed upon melting, the computed conductivity being much larger than found in experiments. Instead, for the Mg-rich alloy, the calculated conductivity approaches closely to the experimental value.

Journal ArticleDOI
TL;DR: In this paper, a semiconductor concept similar to that in boron-rich solids is proposed for the interpretation of the electronic properties of icosahedral quasicrystals.

Journal ArticleDOI
TL;DR: In this article, the effect of growth rate on the crystalline quality of an epilayer was investigated by using X-ray diffraction and electrolyte electroreflectance measurements.

Journal ArticleDOI
TL;DR: In this article, the donor level of the excess electron of carbon coincides with the upper valence band, thus raising the hopping probability within this band, which is consistent with various experimental results.
Abstract: Carbon atoms in the β-rhombohedral boron structure substitute for boron atoms at the polar sites of the B 12 icosahedra. The donor level of the excess electron of carbon coincides with the upper valence band, thus raising the hopping probability within this band. This assumption is consistent with various experimental results. The ionisation energy of the intrinsic electron trapping levels is slightly different for B 12 and B 11 C icosahedra. The photoconductivity and quotient spectra of the reflectivities of differently doped samples indicate carbon-induced changes in the density of states within the energy bands.

Journal ArticleDOI
TL;DR: In this paper, the effect of X-rays, β-rays and UV radiation on the molecular mobility of dermal collagen and skin was characterized by means of thermally stimulated current (TSC) spectroscopy.
Abstract: Radiation effects on collagen and skin have been characterized by means of thermally stimulated current (TSC) spectroscopy. X-rays, β-rays and UV radiation have similar effects on the molecular mobility of dermal collagen and skin. They induce a decrease of intra and intermolecular mobility. The restriction of molecular movement can be explained by an increase of collagen cross-links.

Journal ArticleDOI
TL;DR: In this article, a model for estimating the residual spatial noise in a direct injection readout hybrid focal plane array (FPA) consisting of photovoltaic detectors is presented, which consists of computing the response of the pixels after taking into account the nonlinearity induced by the transfer function in the hybrid configuration and the estimated r.m.s. response nonuniformity from the known input parameters of the detector and readout arrays.

Journal ArticleDOI
TL;DR: In this article, an extensive micro-Raman study, oval-defect-related morphological, compositional and carrier concentration inhomogeneities were studied in MBE-grown GaAs and epitaxial layers.
Abstract: By an extensive micro-Raman study, oval-defect-related morphological, compositional and carrier concentration inhomogeneities were studied in MBE-grown GaAs and epitaxial layers. It was found that the crystalline morphology changes from point to point in the same defect. Though the films remain in a rather good crystalline state, the defects are shown to induce stress/strain in these films. The carrier concentration at the oval defects was also found to be less than at the epitaxial layers.

Journal ArticleDOI
TL;DR: In this article, the linear polarization dependence of the photoluminescence of Al0.08Ga0.92 was investigated for the incident light propagating parallel to the plane of the structure, and the polarization dependent excitonic recombinations exhibited fully polarized behavior of heavy and light-holes for in plane incident electric field vector.

Journal ArticleDOI
TL;DR: In this paper, the pair potential is constructed from an ab initio molecular dynamics method which makes the effective interionic potential self-consistent with the radial distribution functions on the basis of the quantal hypernetted-chain theory.
Abstract: The static and dynamic structure of liquid lithium (470 K) in a computer experiment were investigated using a new type of interaction: the pair potential is constructed from an ab initio molecular dynamics method which makes the effective interionic potential self-consistent with the radial distribution functions on the basis of the quantal hypernetted-chain theory. Comparisons of the new calculations both with data obtained in ab initio simulations and with transport properties show very good agreement and thus justify the use of a more sophisticated interatomic pair potential.

Journal ArticleDOI
TL;DR: In this paper, deep level transient spectroscopy (DLTS) has been used to investigate the Si-related DX center in heavily doped ion-implanted GaAs, and the activation energies of these two two levels are 270 and 315 meV.

Journal ArticleDOI
TL;DR: In this article, the potential modulation of the Shubnikov-de Haas oscillations arising in the magneto-resistance at quantizing magnetic fields has been investigated and compared with theoretical predictions for the so-called Hofstadter butterfly energy spectrum.
Abstract: Lateral superlattices with very small lattice periods approaching the Fermi wavelength in size are fabricated on AlGaAs heterostructures by electron beam lithography. The potential modulation is induced by a gate voltage applied to a laterally modulated gate electrode. In our samples the two-dimensional electron gas is located very close to the sample surface, thus allowing us to induce very small lattice periods with a relatively large amplitude of the potential modulation. For weak potential modulation, which can be tuned by the gate voltage, we observe a modulation of the amplitude of the Shubnikov-de Haas oscillations arising in the magneto-resistance at quantizing magnetic fields. For more negative gate voltages, i.e. larger amplitudes of the potential modulation, certain maxima of the Shubnikov-de Haas oscillations split up reflecting the energy spectrum that arises when a given number of flux quanta penetrates a unit cell of the lattice. We compare our experimental results with theoretical predictions for the so-called Hofstadter butterfly energy spectrum and we conclude that we can experimentally detect the major energy bands and gaps.

Journal ArticleDOI
TL;DR: In this paper, a simple mathematical formulation for determination of temperature profiles of crystal growth furnaces using radiative heat transfer mechanism is presented and the influence of various furnace elements on the profiles are presented.

Journal ArticleDOI
TL;DR: In this article, a comparative study of extracts and residues at various stages of demineralization is presented, showing that biomaterials for orthopaedic prostheses require the same morphology in order to phenomenologically reproduce the same dynamic behaviour.
Abstract: Thermally stimulated current spectroscopy has been applied to the investigation of molecular mobility in human calcified tissue. A comparative study of extracts and residues at various stages of demineralization is presented. Results show that: Biomaterials for orthopaedic prostheses require the same morphology in order to phenomenologically reproduce the same dynamic behaviour.

Journal ArticleDOI
TL;DR: In this paper, the effect of arsenic incorporation at various growth temperatures on the surface morphology, lattice mismatch and photoluminescence has been studied, and the quality of the epilayers has been found to depend strongly on the pre-growth melt dissolution sequence and improves with an increase in growth temperature.

Journal ArticleDOI
TL;DR: In this article, a nominal well width (20 nm) of Al0.08Ga0.92 was constructed by molecular beam epitaxy technique with the aim of obtaining a lasing device.
Abstract: A nominal well width (20 nm) of Al0.08Ga0.92As quantum well structure has been fabricated by molecular beam epitaxy technique with the aim of obtaining a lasing device. The temperature evolution of quantum well photoluminescence was studied in the range 10–300 K which shows excitons being trapped at the interfacial defects below 100 K. The linear polarization effects in the photoluminescence have been studied for the incident and collected light propagating parallel to the plane of the well layer. In a very careful study, the luminescence was found to be fully polarized for the incident electric vector parallel to well layers, while it showed depolarized behaviour for the incident electric vector perpendicular to the well layers. The earlier conclusions based on photoluminescence excitation and absorption studies of heavy- and light-hole emissions are supported. The 20 nm quantum well structure has been corroborated using scanning tunnelling microscopy.

Journal ArticleDOI
TL;DR: In this paper, the Mooij resistivity of liquid alkali-metalloid alloys was explained by assuming that the resistivity in the metalloid-rich alloys is dominated by nearest-neighbour electron hopping on the metal sublattice.
Abstract: It is shown that the Mooij resistivity (that is the resistivity of the alloy composition that has a vanishing temperature coefficient) of liquid alkali-metalloid alloys can be explained by assuming that the resistivity in the metalloid-rich alloys is dominated by nearest-neighbour electron hopping on the metalloid sublattice. The coordination number on the metalloid sublattice determines the Mooij resistivity.

Book ChapterDOI
01 Jan 1996
TL;DR: In this article, a two-terminal and threeterminal QW laser-phototransistor structures, which can generate a laser radiation in short-wavelength infrared range of spectrum modulated by longwavelength IR radiation, have been proposed and evaluated.
Abstract: Quantum-well (QW) structures are utilized in a variety of modern semiconductor devices, for example, in QW lasers and intersubband QW infrared photodetectors1,2 A novel device — the photodetector with optical output has been proposed and studied theoretically3,4 This device consists of a QW photodetector integrated with a light emitting diode Recently such integrated device was fabricated and measured by Liu et al 5 The purpose of the present work is to propose and evaluate two-terminal and three-terminal QW laser-phototransistor structures, which can generate a laser radiation in short-wavelength infrared range of spectrum modulated by long-wavelength infrared radiation (see Figure 1) The operation of the QW laser-transistors in question is connected with the injection of hot electrons into a laser active region or their extraction from it controlled by the potential of the QW specially inserted in the emitter (Figure la) or collector (Figure lb) region