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Effective Mass (effective + mass)
Kinds of Effective Mass Terms modified by Effective Mass Selected AbstractsEffective mass of InN estimated by Raman scatteringPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Jung Gon Kim Abstract We have estimated the longitudinal effective mass (m,) of electron in n-type InN films by Raman scattering. The samples were grown by MOVPE (metal organic vapor phase epitaxy) with free carrier concentration of n =6.7×1018 -9.9×1018 cm -3 according to Hall measurement. A weak Raman signal observed at ,430 cm -1 at room temperature was sharpened and shifted to higher frequency toward the A1(TO)-phonon mode at 447 cm -1 with increasing n. This mode was assigned to the lower branch (L - ) of the longitudinal-optic-phonon-plasmon-coupled (LOPC) mode. The line shape was carefully analyzed by a semi-classical line-shape fitting analysis assuming deformation potential and electro-optic coupling mechanisms for the light scattering process. A line-shape fitting analysis was conducted by adjusting three major parameters; electron density, effective mass and plasmon damping rate. The analysis well reproduced values of electron density and mobility deduced by Hall measurement. Electron effective mass of m,*/m0 = 0.05 (±0.01) was also obtained as the best-fit parameter. The result agrees well with previous data obtained by other optical methods. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Traversing the Metal-Insulator Transition in a Zintl Phase: Rational Enhancement of Thermoelectric Efficiency in Yb14Mn1,xAlxSb11,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2008Eric S. Toberer Abstract For high temperature thermoelectric applications, Yb14MnSb11 has a maximum thermoelectric figure of merit (zT) of ,1.0 at 1273,K. Such a high zT is found despite a carrier concentration that is higher than typical thermoelectric materials. Here, we reduce the carrier concentration with the discovery of a continuous transition between metallic Yb14MnSb11 and semiconducting Yb14AlSb11. Yb14Mn1-xAlxSb11 forms a solid solution where the free carrier concentration gradually changes as expected from the Zintl valence formalism. Throughout this transition the electronic properties are found to obey a rigid band model with a band gap of 0.5,eV and an effective mass of 3 me. As the carrier concentration decreases, an increase in the Seebeck coefficient is observed at the expense of an increased electrical resistivity. At the optimum carrier concentration, a maximum zT of 1.3 at 1223,K is obtained, which is more than twice that of the state-of-the-art Si0.8Ge0.2 flown by NASA. [source] Exactly solvable effective mass Schrödinger equation with coulomb-like potentialINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010C. Pacheco-García Abstract Exactly solvable Schrödinger equation (SE) with a position-dependent mass distribution allowing Morse-like eigenvalues is presented. For this, the position-dependent mass Schrödinger equation is transformed into a standard SE, with constant mass, by means of the point canonical transformation scheme. In that method, the choice of potential for the position-dependent mass Schrödinger equation allows us to obtain the transformation that should be used to find the exactly solvable SE. As a useful application of the proposal, the equivalent of the Witten superpotential is chosen to be constant to find the position-dependent mass distribution and the exactly solvable potential V(m(x)) allowing Morse-type energy spectra. This V(m(x)) is shown to have a Coulomb potential structure and can be useful in the study of the electronic properties of materials in which the carrier effective mass depends on the position. Moreover, the worked example, the approach is general and can be applied in the search of new potentials suitable on the study of quantum chemical systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Unusual Sb,Sb bonding in high temperature thermoelectric materialsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jianxiao Xu Abstract The emerging families of advanced thermoelectrics are dominated by antimonides and tellurides. Because the structures of the tellurides are mostly composed of NaCl-related motifs, they do not contain any Te,Te bonds, and all of the antimonide structures exhibit Sb,Sb bonds of various lengths. Taking all Sb,Sb distances shorter than 3.2 Å into account, the Sb atom substructures are Sb24, pairs in ,-Zn4Sb3, linear Sb37, units in Yb14MnSb11, planar Sb44, rectangles in the skutterudites, for example, LaFe3CoSb12, and Sb8 cubes interconnected via short Sb,Sb bonds to a three-dimensional network in Mo3Sb5Te2. These interactions have a significant impact on the band gap size as well as on the effective mass around the Fermi level, for the bottom of the conduction band is in all cases predominated by antibonding Sb,Sb interactions, and,in some cases,the top of the valence band by bonding Sb,Sb interactions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source] Hydrogenic impurity in two-dimensional semiconductors with anisotropic energy spectrum of carriersLASER PHYSICS LETTERS, Issue 12 2005S. P. Andreev Abstract The binding energy and wave function of a ground state of a shallow hydrogenic impurity in two-dimensional semiconductors with isotropic and anisotropic effective mass of carriers m* = {m,, m,, m,} are derived. The calculations are performed by the variational method based on a two-parametric trial wave function. The dependence of binding energy and deformation of an impurity on 2D layer thickness and effective mass anisotropy parameter m,/m, is investigated. The obtained results are in a good agreement with experimental data and in the limiting cases coincide with the theoretical calculations of shallow impurity binding energy for bulk semiconductors [1] and two-dimensional semiconductors with isotropic effective mass of electrons [2]. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Hole,polar phonon interaction scattering mobility in chain structured TlSe0.75S0.25 crystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009A. F. Qasrawi Abstract In this study, the electrical resistivity, charge carriers density and Hall mobility of chain structured TlSe0.75S0.25 crystal have been measured and analyzed to establish the dominant scattering mechanism in crystal. The data analyses have shown that this crystal exhibits an extrinsic p-type conduction. The temperature-dependent dark electrical resistivity analysis reflected the existence of three energy levels located at 280 meV, 68 meV and 48 meV. The temperature dependence of carrier density was analyzed by using the single donor,single acceptor model. The carrier concentration data were best reproduced assuming the existence of an acceptor impurity level being located at 68 meV consistent with that observed from resistivity measurement. The model allowed the determination of the hole effective mass and the acceptor,donor concentration difference as 0.44m0 and 2.2 × 1012 cm,3, respectively. The Hall mobility of the TlSe0.75S0.25 crystal is found to be limited by the scattering of charged carriers over the (chain) boundaries and the scattering of hole,polar phonon interactions above and below 300 K, respectively. The value of the energy barrier height at the chain boundaries was found to be 261 meV. The polar phonon scattering mobility revealed the high-frequency and static dielectric constants of 13.6 and 15.0, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comment on "Transport Properties of Tl5Te3 Single Crystals" [phys. stat. sol. (a) Vol.PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007329 (2002)], No. Abstract Recently, Gamal et al. [phys. stat. sol. (a) 191, 322 (2002)] reported the results of electrical conductivity, Hall effect and thermoelectric power (TEP) measurements on Tl5Te3 single crystals. The samples used in the study were p-type semiconductors. From the experimental data for the temperature dependence of TEP, Gamal et al. determined the values of 1.6 × 10,41 kg and 1.5 × 10,40 kg, respectively, for the effective masses of electrons and holes in p-type Tl5Te3, which are about ten orders of magnitude smaller than the free electron mass, 9.11 × 10,31 kg. We argue that the anomalously small values obtained for the effective mass of charge carriers in Tl5Te3 have no physical significance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Two-dimensional electrons occupying multiple valleys in AlAsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2006M. Shayegan Abstract Two-dimensional electrons in AlAs quantum wells occupy multiple conduction-band minima at the X-points of the Brillouin zone. These valleys have large effective mass and g -factor compared to the standard GaAs electrons, and are also highly anisotropic. With proper choice of well width and by applying symmetry-breaking strain in the plane, one can control the occupation of different valleys thus rendering a system with tuneable effective mass, g -factor, Fermi contour anisotropy, and valley degeneracy. Here we review some of the rich physics that this system has allowed us to explore. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Manifestation of the equilibrium hole distribution in photoluminescence of n-InNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2005A. A. Klochikhin Abstract Photoluminescence (PL) of n-InN grown by molecular beam epitaxy with Hall concentrations from 3.6 to 7.3 × 1017 cm,3 demonstrates dependences on carrier concentration, temperature, and excitation density which give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The structure of the PL spectra observed at 4.2 and 77 K in the energy interval from 0.50 to 0.67 eV indicates that a considerable part of holes is trapped by deep and shallow acceptors before the interband recombi- nation with degenerate electrons occurs. At room temperature, the band-to-band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by model calculations under the assumptions of a band gap equal to 0.665,0.670 eV at zero temperature and zero carrier concentration and a non-parabolic conduction band with the effective mass at the G -point equal to 0.07 of the free electron mass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the band gap of indium nitridePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003B. R. Nag Abstract The controversy about the band gap of indium nitride is discussed. It is shown by considering the electron effective mass in different direct-gap II,VI and III,V semiconducting compounds that the controversy may be resolved by measuring the electron effective mass in indium antimonide samples showing a band gap of 0.7 eV. [source] Thermo- and galvanomagnetic measurements of semiconductors at ultrahigh pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Vladimir V. Shchennikov Abstract The thermoelectric power, magnetoresistance, and thermomagnetic effects were measured for Te and Se micro-samples in the vicinity of semiconductor,metal phase transitions at high pressure. From longitudinal and transverse Nernst-Ettingshausen effects the scattering parameter r of holes was estimated and a decrease of the effective mass of holes was found during the closing of semiconductor gap. After the high pressure treatment an inversion of the sign of parameter r corresponding to a change of scattering mechanism was observed for the Te sample due to an increase of the density of lattice defects. [source] Effective mass of InN estimated by Raman scatteringPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Jung Gon Kim Abstract We have estimated the longitudinal effective mass (m,) of electron in n-type InN films by Raman scattering. The samples were grown by MOVPE (metal organic vapor phase epitaxy) with free carrier concentration of n =6.7×1018 -9.9×1018 cm -3 according to Hall measurement. A weak Raman signal observed at ,430 cm -1 at room temperature was sharpened and shifted to higher frequency toward the A1(TO)-phonon mode at 447 cm -1 with increasing n. This mode was assigned to the lower branch (L - ) of the longitudinal-optic-phonon-plasmon-coupled (LOPC) mode. The line shape was carefully analyzed by a semi-classical line-shape fitting analysis assuming deformation potential and electro-optic coupling mechanisms for the light scattering process. A line-shape fitting analysis was conducted by adjusting three major parameters; electron density, effective mass and plasmon damping rate. The analysis well reproduced values of electron density and mobility deduced by Hall measurement. Electron effective mass of m,*/m0 = 0.05 (±0.01) was also obtained as the best-fit parameter. The result agrees well with previous data obtained by other optical methods. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] InGaAs channel MOSFET with self-aligned source/drain MBE regrowth technologyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2009Uttam Singisetti Abstract InGaAs is a promising alternative channel material to Si for sub-22 nm node technology because of its low electron effective mass (m*) hence high electron velocities. We report a gate-first MOSFET process with self-aligned source/drain formation using non-selective MBE re-growth, suitable for realizing high performance scaled III-V MOSFETs. A W/Cr/SiO2 gate stack was defined on thin (4 nm/2.5 nm) InGaAs/InP channel by an alternating selective dry etch technique. A 5 nm Al2O3 layer was used as gate dielectric. An InAlAs bottom barrier provided vertical confinement of the channel. An in-situ H cleaning of the wafer leaves an epi-ready surface suitable for MBE or MOCVD regrowth. Source/Drain region were defined by non-selective MBE regrowth and in situ molybdenum contacts. First generation of devices fabricated using this process showed extremely low drive current of 2 ,A/,m. The drive current was limited by an extremely high source resistance. A regrowth gap between source/drain and gate was the cause for high source resistance. The gap in the regrowth was because of low growth temperature (400 °C). A modified high temperature growth technique resolved the problem. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of external magnetic field and confinement on spectrum rearrangement and exciton polaritons in optical microcavityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Natalia Kaputkina Abstract Influence of external magnetic field and confinement on direct and spatially-indirect excitons is studied. Exciton-photon interaction and exciton polariton formation are discussed for single and coupled quantum wells or quantum dots embedded in optical microcavity. Possibility to control polariton resonance, polariton splitting and polariton dispersion by magnetic field is studied analitically and numerically. Magnetic field changes effective mass of magnetoexciton. Magneticfield increases effective steepness of confining potential in quantum dots also. This leads to the transformation of exciton energy spectrum. At low temperatures spontaneous coherence and Kosterlitz-Thouless transition to superfluid state of exciton polaritons in the system of coupled quantum wells embedded in microcavity or Bose-Einstein condensation of exciton polaritons in the system of coupled quantum dots embedded in optical microcavity can take place. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theory of electronic structure of BGaAs and related alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008A. Lindsay Abstract Previous experiments on BxGa1,xAs containing a few percent boron show a dramatic increase in electron effective mass, m*e, similar to that observed in many GaNxAs1,x samples. By contrast, there is a near-linear blue-shift of the energy gap, which can be conventionally described using the virtual crystal approximation. We use a tight-binding model to show that isolated B atoms have little effect either on the band gap or lowest conduction band dispersion in BxGa1,xAs. By contrast, B pairs and clusters introduce defect levels close to the conduction band edge (CBE) which, through a weak band-anticrossing (BAC) interaction, significantly reduce the band dispersion in and around the , -point, thus accounting for the strong increase in m*e and reduction in mobility observed in these alloys. Calculations show that replacing gallium by aluminium shifts the CBE upwards, leading to a large density of B-related states in the energy gap. By contrast, indium shifts the band edge downwards, leading eventually to a band edge m*e close to that predicted by the virtual crystal approximation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Carrier transport studies of dichromatic InGaN-based LEDs with spacer bandgap dependencePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Shih-Wei Feng Abstract Carrier transport of dichromatic InGaN-based LEDs with AlGaN spacer bandgap dependence has been studied. TREL measurements show that carrier dynamics could be well explained by the combined effects of carrier effective mass, carrier mobility, quantum confinement, and device structures. The experimental results provide important information for device designs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excited states and spontaneous transition lifetimes of donor impurities in quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007G. Murillo Abstract We calculate the 2p,1s-like transition energy and the spontaneous lifetime of an on-center shallow donor impurity in a spherical parabolic GaAs-(Ga,Al)As quantum dot (PQD) as a function of the radius of the structure and the strength of an applied electric field. In our calculations we use a variational method, within the effective mass and dipolar approximations. We find that the spontaneous lifetimes increase with the radius of the PQD and the applied electric field. In this direction our results revel that the electric field can be used to suppress the electron-phonon interaction driving to the increasing of the 2p-1s spontaneous life-time, showing the feasibility of using impurity states to be used in quantum computing developments. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of lattice-mismatch induced built-in strain on the valence band properties of wurtzite ZnO/Zn1,xMgxO quantum well heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007K. Zitouni Abstract We present a theoretical study of the effects of lattice-mismatch induced built-in strain on the electronic properties of valence band states in wurtzite ZnO/Zn1,xMgxO Quantum Well (QW) heterostructures. In this purpose, a 6x6 k·p method has been used to incorporate the effects of strain and nonparabolicity. The energies corresponding to the transitions between conduction band (C), heavy hole (HH), light hole (LH) and crystal-field split-off hole (CH) bands have been calculated as a function of Mg composition and strain. We have also calculated the energy dispersions and wave functions of strained wurtzite ZnO. It is found that ZnO is always under a biaxial tensile strain, in the whole Mg composition range investigated (x < 40%). As a consequence, the light hole valence subband is shifted upwards with respect to the corresponding heavy hole valence subband, resulting in a reduction of ZnO direct band gap by almost 6% when x = 35%. This is found to result in turn in a significantly reduced in-plane hole effective mass at the top of the valence band which is always LH-like. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Anisotropy of the ,-point effective mass and mobility in hexagonal InNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006T. Hofmann Abstract We determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration N from 1.8 × 1017 cm,3 to 9.5 × 1018 cm,3 using Infrared Magneto-optic Generalized Ellipsometry. The room-temperature measurements were carried out with magnetic fields up to 4.5 T. For the ,-point we estimate m*, = 0.047m0 and m*, = 0.039m0 for polarization perpendicular and parallel to the c -axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c -axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Breakdown of Casimir invariance in curved space-timeANNALEN DER PHYSIK, Issue 8 2010D. Singh Abstract It is shown that the commonly accepted definition for the Casimir scalar operators of the Poincaré group does not satisfy the properties of Casimir invariance when applied to the non-inertial motion of particles while in the presence of external gravitational and electromagnetic fields, where general curvilinear co-ordinates are used to describe the momentum generators within a Fermi normal co-ordinate framework. Specific expressions of the Casimir scalar properties are presented. While the Casimir scalar for linear momentum remains Lorentz invariant in the absence of external fields, this is no longer true for the spin Casimir scalar. Potential implications are considered for the propagation of photons, gravitons, and gravitinos as described by the spin-3/2 Rarita-Schwinger vector-spinor field. In particular, it is shown that non-inertial motion introduces a frame-based effective mass to the spin interaction, with interesting physical consequences that are explored in detail. [source] Density functional crystal orbital study of cyano-substituted poly(para -phenylene-vinylene) and poly(quinoxaline-vinylene)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2006F. Bartha Abstract We have calculated the optical and electronic properties of several conjugated organic polymers: poly(p -phenylene-vinylene) (PPV) and its derivatives. Cyano substitutions on the phenylene ring: poly(2,5-dicyano- p -phenylene-vinylene) (2,5-DCN-PPV) and on the vinylene linkage: poly(p -phenylene-7(,8)-(di)cyano-vinylene) are considered. In addition, poly(quinoxaline-vinylene) (PQV) is studied. The infinite isolated quasi-1D chains are treated with periodic boundary conditions, using atomic basis sets. In a comparative study of PPV, some issues regarding the selection of the functionals and basis sets are discussed and excitation energies derived from time-dependent and from ordinary methods are compared. It is concluded that for these polymers the calculations are informative at the B3LYP/6-31G** density functional theory (DFT) level. The absolute values might change with improved methods, but the similarity of the polymers suggests that the relative characterization is adequate. Band structures are communicated along with characteristics of the highest occupied and the lowest unoccupied crystal orbitals (HOCO and LUCO). Electron affinities, ionization potentials, valence and conduction bandwidths, and effective masses at the bandgap are given. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Comment on "Transport Properties of Tl5Te3 Single Crystals" [phys. stat. sol. (a) Vol.PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007329 (2002)], No. Abstract Recently, Gamal et al. [phys. stat. sol. (a) 191, 322 (2002)] reported the results of electrical conductivity, Hall effect and thermoelectric power (TEP) measurements on Tl5Te3 single crystals. The samples used in the study were p-type semiconductors. From the experimental data for the temperature dependence of TEP, Gamal et al. determined the values of 1.6 × 10,41 kg and 1.5 × 10,40 kg, respectively, for the effective masses of electrons and holes in p-type Tl5Te3, which are about ten orders of magnitude smaller than the free electron mass, 9.11 × 10,31 kg. We argue that the anomalously small values obtained for the effective mass of charge carriers in Tl5Te3 have no physical significance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of the electrical conductivity and thermoelectric power of In2Te5 single crystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2003M. M. Nassary Abstract In the present study, single crystals of defect semiconductor In2Te5 were grown by the Bridgman technique. An investigation was made on the Hall effect, electrical conductivity and thermoelectric power of In2Te5 monocrystal in the temperature ranging from 200 to 500 K. The investigated samples were P-type conducting. The Hall coefficient yields a room-temperature carrier concentration of (7.7 × 109 cm,3). The bandgap was found to be (,Eg = 0.993 eV). Hence, a combination of the electrical conductivity and Hall effect measurements enable us to study the influence of temperature on the Hall mobility (,) and to discuss the scattering mechanism of the charge carriers, also the present investigation involves thermoelectric power measurements of In2Te5 single crystal: these measurements enable us to determine many physical parameters such as carriers mobilities, effective masses of free charge carriers (mp*, mn*, diffusion coefficients (Dp, Dn) and diffusion lengths as well as the relaxation time (,p, ,n). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-field de Haas,van Alphen effect in GdIn3PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003Z. Kletowski Abstract Results of the de Haas,van Alphen effect investigations are reported for the antiferromagnetically ordered compound GdIn3. For the first time data on the dHvA frequencies and their angular dependencies are shown for magnetic field higher than the metamagnetic transition field. The list of detected frequencies and related cyclotron masses is given. Among many Fermi surface branches observed, only the j, b and d correspond to theoretically predicted and experimentally observed branches for the nonmagnetic LaSn3. The metamagnetic transition taking place at 30 T in the GdIn3 influences some branches of Fermi surface, mostly those in the (110) plane and close to the [111] direction. All effective masses found are lower than m0 and close to those found for the LaSn3. [source] The band structure of a layered Hg3TeCl4 crystal formed by energy states of HgCl2 and HgTe crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008M. Sznajder Abstract The ab-initio calculated band structure of a not as yet investigated orthorhombic Hg3TeCl4 crystal (Pbca, D152h) was analyzed by means of the elementary energy-bands concept. It was demonstrated that this band structure originates from that of a layered HgCl2 dielectric deformed by the presence of the HgTe structural elements. Further, it was revealed that the valence band of Hg3TeCl4 is composed of the 8-branch elementary energy bands corresponding to the actual Wyckoff position c (x, y, z) of D152h group that indicates the presence of ionic and covalent contributions to the chemical bonding in the crystal. The existence of Davydov splitting in the 8-branch elementary energy band situated in the low-energy range of the valence band was observed, which is typical for layered crystals with a weak interlayer interaction between translationally nonequivalent structural units. It was shown that the anisotropy of the electron and hole effective masses does not correspond to the macroscopic anisotropy of the crystal and an explanation of this behaviour was proposed. The obtained parameters of the crystal (direct energy gap Eg = 2.49 eV as well as values of the estimated electron effective masses) indicate that it could find an application in optoelectronics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ab-initio investigation of structural, electronic and optical properties for three phases of ZnO compoundPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2007Z. Charifi Abstract The complex density-functional theory (DFT) calculations of structural, electronic and optical properties for the three phases: wurtzite (B4), zincblende (B3) and rocksalt (B1) of ZnO compound have been reported using the full-potential linearized-augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We employed both the local-density approximation (LDA) and the generalized-gradient approximation (GGA), which is based on exchange,correlation energy optimization to calculate the total energy. Also, we have used the Engel,Vosko GGA formalism, which optimizes the corresponding potential for band-structure calculations. The 3d orbitals of the Zn atom were treated as the valence band. The calculated structural properties (equilibrium lattice constant, bulk modulus, etc.) of the wurtzite and rocksalt phases are in good agreement with experiment. The B4 structure of ZnO is found to transform to the B1 structure with a large volume collapse of about 17%. The phase transition pressure obtained by using LDA is about 9.93 in good agreement with the experimental data. B1-ZnO is shown to be an indirect bandgap semiconductor with a bandgap of 1.47 eV, which is significantly smaller than the experimental value (2.45 ± 0.15 eV). While B3 and B1 phases have direct bandgap semiconductors with bandgaps 1.46 and 1.57 eV, respectively. Also, we have presented the results of the effective masses. We present calculations of the frequency-dependent complex dielectric function , (,) and it zero-frequency limit ,1(0). The optical properties of B4 phase show considerable anisotropic between the two components. The reflectivity spectra has been calculated and compared with the available experimental data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The electronic structure of chalcopyrites,bands, point defects and grain boundariesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2010Susanne Siebentritt Abstract We summarize the progress made recently in understanding the electronic structure of chalcopyrites. New insights into the dispersion of valence and conduction band allow conclusions on the effective masses of charge carriers and their orientation dependence, which influences the transport in solar cell absorbers of different orientation. Native point defects are responsible for the doping and thus the band bending in solar cells. Results of optoelectronic defect spectroscopy are reviewed. Native defects are also the source for a number of metastabilities, which strongly affect the efficiency of solar cells. Recent theoretical findings relate these effects to the Se vacancy and the InCu antisite defect. Experimentally determined activation energies support these models. Absorbers in chalcopyrite solar cells are polycrystalline, which is only possible because of the benign character of the grain boundaries. This can be related to an unusual electronic structure of the GB. Copyright © 2010 John Wiley & Sons, Ltd. [source] Angular and temperature-related specific features of averaging of hole effective masses in p-Ge at low temperaturesANNALEN DER PHYSIK, Issue 12 2009T. Tisnek Abstract Microwave magnetoresistance of lightly doped (nondegenerate) p-Ge has been studied by the electron spin resonance method, which can record the derivative of the microwave absorption with respect to the magnetic field. The change in the absorption is proportional to that in the conductivity of the semiconductor in the magnetic field (magnetoresistance). It was found that the averaging time of the light and heavy holes effective masses depends on temperature and on the magnetic field direction in a sample. An analysis of the derivative made it possible to determine regions of the fastest effective mass averaging. [source] | ||||||||||||||||