bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of nonparabolieity on self‐consistent treatment for GaAsAlxGa1–xAs heterojunction
Authors: Milanović V. , Tjapkin D. , Šašić R. 
Published: July 2007

AbstractThe self‐consistent determination is analysed of the relevant parameters of a GaAsAlxGa1–xAs heterojunction in the presence of nonparabolicity of bands. Starting from Kane's theory, a suitable form of the Schrödinger equation for electrons is given. It is shown that there are, generally, two different energy spectra. The notion of an extended effective mass is introduced, which are depending on the potential, the energy gap, and subband index. The numerical analysis of results is performed on GaAsAl0.4Ga0.6As heterojunction. These numerical results confirm theoretical conclusions exposed in the first part of the paper.
Raman scattering studies of mobile ions in superionic conductor hollandites
Authors: Shibata Y. , Suemoto T. , Ishigame M. 
Published: July 2007

AbstractThe Raman spectra of the superionic conductors K1.6Mg0.8Ti7.2O16, Cs1.2Mg0.6Ti7.4O1.6, and (KTI)1.6Mg0.8Ti7.2O16 are measured in the frequency range from 5 to 1000 cm−1. In the range from 100 to 1000 cm−1 Raman spectra hardly show alkali ion dependence. On the contrary, in the frequency range from 5 to 100 cm−1, an additional Raman band is observed. This Raman band shows alkali ion dependence. By using the Frenkel‐Kontorova model for the hollandite crystal with the given configuration of the mobile ions, it is found that the dependence of vibrational frequency of mobile ions with kinds of alkali ion is well explained and that the concept of “super unit cell” that is introduced by Beyeler is very useful to explain the Raman bands which are observed below 100 cm−1 in hollandite crystals.
Dislocation core models and their positron annihilation effects
Authors: Shen J. Q. , Lung C. W. , Wang K. L. 
Published: July 2007

AbstractPositron annihilation parameters with three simplified dislocation core models are calculated. The positron annihilation effect at a dislocation line is mainly contributed by the dislocation core. The positron annihilation effects at pure dislocation lines are large enough to be measurable though they are much weaker than at vacancies.
Low‐temperature properties of antiferromagnetic GdRhxSny, compound
Authors: Rojek A. , Sulkowski C. , Zygmunt A. , Kozlowski G. 
Published: July 2007

AbstractMagnetic and electric resistivity measurements on single crystals of GdRh1.07Sn4.21 compound are performed. The compound is antiferromagnetic with a Néel temperature TN = 11.6 K. The temperature dependence of resistivity has four temperature regions: T3/2, T2, T, and ln T. The data are considered in terms of coexistence of local moment antiferromagnetism of the Gd atoms and localized spin fluctuations (lsf) or itinerant electron ferromagnetism of the Rh atoms.
Spontaneous hall effect and magnetization of Fe–(B, Zr) and Co– Mo amorphous films
Authors: Stobiecki T. , Pbzybylski M. 
Published: July 2007

AbstractAmorphous Fe1–x(B, Zr)x and Co1‐x(B, M.o)x films are prepared by the rf sputtering technique over a wide range of concentration where the alloys show ferromagnetism. From the magnetization and mean hyperfine field values at low temperatures the magnetic moment of Fe(μFe) is determined. Using a rigid‐band model the charge transfer per ß and Zr atom to the Fe d‐band is calculated. The best fits are obtained for a charge transfer of 1.48 electrons per ß atom and of 1.8 electrons per Zr atom, yielding the observed critical concentrations at which ferromagnetism disappears: xc = 0.6 and Xc = 0.5 for FeB and FeZr films, respectively. From spontaneous Hall effect and resistivity (ϱ) measurements it is obtained thatRs ∼ ϱn in a wide range of concentrations with an exponent n = 1.97. The side jump parameter (Δy) calculated from the free‐electron Berger formula decreases with increasing concentration of non‐magnetic elements of the alloy. This tendency is similar as in the case of magnetic moment. The observed correlation between Δy and μFe shows that both parameters are of the same origin.
Charge ordering in intermediate‐band crystals
Authors: Ionova G. V. , Kosteubov Yu. N. , Nikolaev A. V. 
Published: July 2007

AbstractThe charge ordering phenomena in intermediate band crystals are considered using the extended Hubbard Hamiltonian as a model. The average 〈a+iaj〉 is taken into account for describing the delocalized electron density. The new criterion of the charge‐ordered state existence, including the boundary condition for the bandwidth, is formulated.
The temperature dependence (4.2 to 293 K) of the resonance energies of excitonic transitions in II–VI compounds
Authors: Dmitrenko K. A. , Shevel S. G. , Taranenko L. V. , Marintchenko A. V. 
Published: July 2007

AbstractExcitonic reflectivity spectra R(hw) are measured by a digital technique for a number of II–VI compounds within a wide temperature range from 4.2 up to 293 K. The exact position of exciton resonance energy within the experimental R(hw) profiles is determined by comparison with reflectivity curves calculated in the model of bulk excitonic oscillator with classical dispersion and exciton‐free surface layer. The temperature dependences of exciton resonance energies thus obtained are found to satisfy the known Varshni formula which includes two empirical parameters. These are determined for each compound under study, so that reference data become available for the position of exciton resonance at any temperature ranging from 4.2 up to 293 K.
Optical properties of α‐ and β‐CuZn brasses in the region of quantum absorption
Authors: Sasovskaya I. I. , Korabel V. P. 
Published: July 2007

AbstractThe optical constants n and k of CuZn brasses with Zn content of 39, 40, 41, 47, 50 at% (β‐phase) and 35 at% (α‐phase) are measured at 293 K, and with Zn content of 35, 39, and 50 at% at 78 K also, in the 1 to 0.25 μm spectral range by the polarimetric method. From n and k reflectance R(λ), high‐frequency conductivity σ(ω) (where ω is the light wave cyclic frequency), the real and imaginary parts ε1(ω) and ε2(ω) of the complex dielectric constant, and the electron characteristic loss function ε/ε + ε are derived. Their concentration and temperature dependences are analyzed. The different characters of the concentration and temperature dependences of the absorption edge of α‐ and β‐brasses confirm that its origin in these alloys is not the same: in α‐brasses the edge is formed by interband transitions from EF to vacant states of the conduction band, while in β‐brasses by d‐band to EF transitions. No substantial change in the optical interband absorption is observed in both, the concentration and temperature (martensitie) b.c.c. to f.c.c. transitions.
Phonon wind generation in Ge by C02 laser induced heating of electron‐hole drops
Authors: Manenkov A. A. , Mikhailova G. N. , Sokolov S. Yu. , Tikhodeev S. G. 
Published: July 2007

AbstractThe processes occurring at high power CO2 laser pulse irradiation (λ = 10.6 (μm, t = 100 ns) of electron‐hole drops (EHD) in Ge are analyzed. It is shown that the features of the recombination radiation and microwave conductivity kinetics of the sample after CO2 laser pulse at intensities up to 105 to 106 W/cm2 are associated with recondensation of the evaporated EHD and with a phonon wind produced driving of nonequilibrium carriers. A theoretical model of phonon wind is suggested taking into account the delay between emission and absorption of the phonons. In comparing the theory with experiments a portion of the IR radiation quanta energy involved in the phonon wind generation is determined. The thermalisation channels of hot carriers are analysed.
Effects of a thin curved transition layer on surface polaritons. Local states
Authors: Wendler L. , Pechstedt E. 
Published: July 2007

AbstractWhen a thin curved transition layer is placed on a semi‐infinite dipole‐active substrate, local states exist in the spectrum of surface polaritons. The dispersion relation and the electromagnetic fields are derived analytically in an explicit form for the case of resonance of the transition layer excitations with the surface polaritons. The spatial dependence of the electric field of the local states is presented in graphical form. It is shown that the field is localized sharply and enhanced within the characteristic distance of the valley in the surface profile of the transition layer.
The magnetic contribution to electrical resistivity in thin gadolinium films
Authors: Urbaniak‐Kucharczyk A. 
Published: July 2007

AbstractThe magnetic contribution to the electrical resistivity in thin magnetic films for the special case of h.c.p. structure is derived. Special attention is given to anomalies due to the magnetic phase transition. The numerical results obtained for the case of polycrystalline gadolinium films show the resistivity dependence on the film thickness and the surface properties.
The temperature dependence of the AC hopping conductivity of lightly compensated semiconductors
Authors: Klimkovich B. V. , Poklonski N. A. , Stelmakh V. F. 
Published: July 2007

AbstractThe temperature dependence of the ac hopping conductivity of lightly compensated semiconductors is explained by taking into account the transitions of a hole within three donor clusters. The effect of the defect wave function anisotropy is discussed. The anisotropy does not change the temperature and frequency dependence of the conductivity. The results are compared with experimental data on Si:P and Ge:P.
The absolute “lattice parameter” of crystals with defects measured with X‐ray methods
Authors: Habtwig J. , Hoiý V. 
Published: July 2007

AbstractThe physical meaning and the physical contents of a “lattice parameter” of a finite crystal with statistically distributed small defects is given. After a short discussion of the problem of defect models and of the elastic state of a finite crystal with defects, appropriate dynamical theories to treat the given problem are discussed. On the basis of a dynamical theory of X‐ray diffraction for crystals with statistically distributed defects in the coherent approximation an expression for the basis vectors of the unit cell of this kind of deformed crystals is derived.
Magneto‐optical measurements in Zn1‐xMnxTe with high manganese concentration
Authors: Desjardins‐Deruelle M. C. , Lascaray J. P. , Coquillat D. , Triboulet R. 
Published: July 2007

AbstractMeasurements of magnetoreflectivity and magnetization are performed on ZnMnTe alloys with Mn concentration x = 0.25 and .x = 0.45 for magnetic fields up to 5.5 T. The exchange constants α and ß are evaluated and compared to previous data. Magnetic circular dichroism measurements are performed in the temperature range 4.2 to 200 K for 0.25 < x < 0.71, to determine the variation of the energy gap as a function of the temperature and the Mn concentration.
Effect of carrier degeneracy on the screening length in degenerate tetragonal semiconductors
Authors: Mondal M. , Gnatak K. P. 
Published: July 2007

AbstractAn attempt is made to study the effect of carrier degeneracy on the Debye screening length of the carriers in tetragonal semiconductors taking degenerate n‐Cd3As2 as an example. It is found on the basis of the Karavaev and Borisenko model, which includes all types of anisotropies in the energy spectrum and has recently been demonstrated in the literature to be the most valid model for Cd3As2, that the screening length decreases with increasing carrier concentration as expected for degenerate semiconductors. Moreover, the tetragonal crystal field effectively reduces the same length with increasing amount of reduction with decreasing electron concentration. The corresponding results for isotropic parabolic energy bands are also obtained from the expressions derived.
Optical spectra and energy band structure of layer‐type AIVBVI compounds
Authors: Valiukonis G. , Guseinova D. A. , Keivaitb G. , Sileika A. 
Published: July 2007

AbstractThe electroreflectance and absorption spectra as well as the hydrostatic pressure dependence of the fundamental absorption edge of GeS, GeSe, SnS, and SnSe crystals are investigated in polarized light. The lowest direct energy gaps are found to be 1V1— 1V1 (E | | a) and 1Λ4— 1Λ4 (E || b) for Ge and Sn monochalcogenides, respectively. The pressure coefficient of the energy gap 1Λ4— 1Λ4 dE/AP = = — (1.3 ± 0.1) × 10−4 eV/MPa of SnSe and SnS is almost twice larger than that of the gap 1V1— 1V1 in GeSe, GeS, and SnSe. On the basis of these investigations, different absorption mechanisms responsible for the fundamental absorption edge are discussed.
Excitation und deexcitation of Tm3+ centres in ZnS involving “External” Excited States
Authors: Zimmermann H. , Boyn R. 
Published: July 2007

AbstractThe excitation and thermal quenching behaviour of two Tm3+ centres in ZnS crystals are studied by measuring broad‐band excitation spectra and the temperature dependence of the decay time, (τ), of the blue 1G4, → 3H6, emission of samples with different codopants. It is shown that these centers possess “external” excited states which manifest themselves by excitation peaks and τ(T) dependences characteristic of the centre investigated. Values are given of the transfer rates from the external to the 4f states, which lie between 1010 and 1012s−l. It is believed that the occurrence of external states is a general property of RE3+ centers in 11‐VI compounds and that these states, in many cases, have a crucial effect on luminescence yield.
Piezoelectric and deformation potential acoustic scattering mobility of a two‐dimensional electron gas in quantum wells
Authors: Chattopadhyay D. 
Published: July 2007

AbstractThe piezoelectric‐scattering mobility in a semiconductor quantum well is evaluated incorporating the effect of the finite width of the structure. The mobility is found to be enhanced in wider channels, but the effect is smaller than that in the case of deformation‐potential acoustic scattering. The combined screened mobility due to deformation potential acoustic and piezoelectric scattering using the Fcrmi‐Dirac statistics is seen to vary inversely with the temperature over the range of about 20 to 60 K. The slope of this variation is greater for smaller electron concentration and wider channels.
A pseudopotential approach to the disorder effects in III‐V ternary semiconductor alloys
Authors: Ito T. 
Published: July 2007

AbstractDisorder effects for bond lengths, lattice parameters, and mixing enthalpies in III‐V ternary semiconductor alloys are investigated using a pseudopotential perturbation treatment. The calculated results are improved by taking into account both, chemical and structural disorder effects. A bimodal distribution of anion‐cation bond lengths, lattice parameter congruence with Vegard's law, and a mixing enthalpy in reasonable agreement with experimental results are obtained.
Heisenberg‐type and double exchange in mixed‐valence clusters
Authors: Belinskii M. I. , Ya. Gamurar V. , Tsukerblat B. S. 
Published: July 2007

AbstractA theory of the vibronic reduction of the energy levels of transition metal mixed valence clusters is developed. The 2T2(t2) ‐ 3T1(t)‐type system is considered in detail. The vibronic model takes into account the interaction with the totally symmetric (A1) mode as well as the interaction with the Jahn‐Teller tetragonal (E) displacement of each d‐ion ligand. The dispersion of crystal vibrations is considered. The correlation interionic interactions via the phonon field are found and discussed in detail. It is indicated that the Heisenberg‐type exchange interaction is partially reduced by the Jahn‐Teller interaction, and the expressions for the reduction factors are calculated. The double exchange parameter is reduced completely by Jahn‐Teller and totally symmetric vibrations. It is shown that the reduction of the double exchange leads to the antiferromagnetic ground state in mixed valence systems with ferromagnetic sround state arising from the double exchange.
Localization of excitons in space‐charge layers
Authors: Kiselev V. A. , Novikov B. V. , Batyrev A. S. , Ubushiev E. A. , Cherednichenko A. E. 
Published: July 2007

AbstractExciton localization in near‐surface regions of semiconductors is discussed. Various mechanisms are listed responsible for the effect based on the binding of the excitons by nearsurface imperfections in crystals. One of the most important mechanisms of the localization is the Stark‐effect on excitons in space‐large layers of semiconductors. It is accounted for in the numerical computation of the exciton reflectance. Essential is a nonuniform character of the electric field. The localization is accompanied by a large enhancement of the exciton reflectance and the appearance of a low‐energy spike in the reflection lineshape. The computed lineshapes are typical of the A n = 1 exciton in a number of CdS and CdSe samples. It is shown that the increase of the bulk damping from 1 to 5 em−1 diminishes the influence of localization and transforms the enhanced lineshapes to the ideal form. The latter is typical of the B‐type excitons in the same crystals. This finding resolves the paradox of different sensitivity of the A‐ and B‐excitons to various (nondestructive) treatments of the surfaces. It explains also the anomalous behaviour of the minimal reflectance with temperature in CdS reported recently in the literature.
Excitonic spectra in 1, 2, 3 dimensions a numerical approach
Authors: Zimmermann R. 
Published: July 2007

AbstractThe Green's function of the Schrödinger equation is used to develop an efficient method for calculating excitonic spectra in d dimensions. The complex dielectric function (including broadening) near the band gap is found by a numerical integration of the exciton equation in real space. Model calculations are presented for the dynamically screened exciton in d = 3, the exciton in an MQW layer (d = 2), and the diamagnetic exciton (d = 1).
Energy transfer processes between Ten centres in ZnS:Te and CdS:Te
Authors: Heimbrodt W. , Goede O. 
Published: July 2007

AbstractZnS:Te, CdS:Te, and (Zn, Cd)S:Te crystals are studied by photoluminescence emission and excitation spectroscopy and by thermal and optical quenching measurements. In ZnS:Te besides the well‐known uv and blue emission bands caused by Te1 and Te2 centres, respectively, a new lower‐energy emission band is found at higher Te concentrations which has to be ascribed to the radiative annihilation of excitons bound to Te3 clusters consisting of three Te impurities on nearestneighbour anion sites. The exciton binding energies and Franck‐Condon relaxation energies of the various Ten centres are discussed. The energy transfer between the Ten centres in ZnS:Te and CdS:Te is studied and quantitatively analyzed in the framework of a kinetic model. In the lowtemperature region a radiationless resonant energy transfer dominates whereas at higher temperatures a thermal release of the bound excitons followed by an exciton‐recapturing by other Ten centres occurs. The observed optically induced energy transfer from Te2 to Te1 centres in ZnS is discussed on the basis of a configuration‐coordinate model.
Effect of alloy composition on the thermoelectric power in inversion layers on ternary semiconductors in the presence of a classically large magnetic field
Authors: Ghatak K. P. , Mondal M. 
Published: July 2007

AbstractAn attempt is made to derive in the presence of a classically large magnetic field expressions for the thermoelectric power of the carriers in n‐channel inversion layers on ternary semiconductors under both, weak and strong electric field, limits. It is found, taking n‐channel inversion layers on Hg1−xCdx, Te as examples, that the same power, for both the limits, increases with increasing alloy composition. The corresponding results for parabolic semiconductors are also obtained from the expressions derived.
Influence of charge transfer on ab initio calculated impurity resistivities in noble metals
Authors: Lodder A. , Mertig I. , Zeller R. , Mrosan E. , Dederichs P. H. 
Published: July 2007

AbstractA method is proposed to obtain values for the impurity resistivity, given an alloy potential. Correct single‐site values which account for the bandstructure of the host and which are calculated by solving the Boltzmann transport equation form the starting‐point. Effects due to charge transfer and lattice distortion can be estimated reliably using an approximate finite‐cluster model method. The selfconsistent potentials for impurities in copper and silver represent correctly the differences between the sp impurities and the 3d and 4d impurities in a host and also the difference between the two hosts for a given impurity. The agreement of the absolute values with experiment is not yet satisfactory.
Energies and Structures of (111) Coincidence Twist Boundaries in 3C‐SiC, Diamond, and Silicon
Authors: Kohyama M. , Yamamoto R. , Doyama M. 
Published: July 2007

AbstractThe energies and structures of (111) coincidence twist boundaries in covalent crystals, 3C‐SiC, diamond, and silicon are calculated for the first time using the tight‐binding type electronic theory (bond orbital model). The repulsive interactions between atoms at short distances are expressed by Born‐Mayer potentials. After lattice relaxation, the energies of the twist boundaries do not scale with the Σ‐values in each material.
Charged Elementary Excitations in Anthracene Polymers. A Systematical Electrical and EPR Study as a Function of Doping
Authors: Grigoryan L. S. , Kharutyunyan I. L. , Matnishyan A. A. , Nikogosyan R. S. , Sharoyan E. G. 
Published: July 2007

AbstractA systematical study of electrical conductivity and EPR of iodine‐doped anthracene polymers (C14H6Ix)n is carried out within a wide range of iodine concentrations (0.07 ≦ x ≦ 0.85). The room temperature electrical conductivity has a broad maximum near x = 0.5. No metallic‐type conduction is observed. The intensity of EPR signal for all of the investigated samples depends on temperature according to the Curie law and has a minimum near x = 0.19. A clear decoupling of paramagnetism with iodine concentration and electrical conductivity is detected. An idealized model of the structure of (C14H6Ix)n including polarons and bipolarons is proposed. On the base of the model a mechanism of generation and compensation of spin and charge during the doping process is discussed and an interpretation of experimental data is given.
Electron Mobility in Heavily Doped Strongly Compensated ZnSe Crystals
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractIn the temperature range 1.65 to 300 K the temperature dependence of the electron mobility is studied in n‐ZnSe crystals with a concentration of electrically active impurities ranging from 7 × 1015 to 5 × 1018 cm−3 and a compensation degree of 0.16 to 0.98. The anomalously low values of the electron mobility and its sharp change with temperature by a power law with an exponent 2 to 4 in heavily doped strongly compensated crystals are accounted for by the specific character of conductivity and Hall effect in samples with a random large scale impurity potential rather than by the peculiarities of the electron scattering. The dependence of the electron mobility on the concentration and the degree of impurity compensation is studied.
The Effect of Temperature and Coupling Strength on the Thermoelectric Power in the Small‐Polaron Hopping Regime
Authors: Triberis G. P. 
Published: July 2007

AbstractThe effect of temperature and coupling strength on the thermoelectric power of the small‐polaron hopping disordered regime is investigated. The thermoelectric power is evaluated for the high‐and low‐temperature case assuming the electron‐lattice interaction to be weak. Results are also given for the low‐temperature and strong‐coupling case. The “macroscopic” thermoelectric power of the material is evaluated for the low‐temperature regime.