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Showing papers on "Effective mass (solid-state physics) published in 1998"


Journal ArticleDOI
Craig Pryor1
TL;DR: In this paper, the electronic structure of pyramidal shaped InAs/GaAs quantum dots was calculated using an eight-band strain-dependent Hamiltonian, and the influence of strain on band energies and the conduction-band effective mass were examined.
Abstract: The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain-dependent $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single-particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four, and six bands, and with results from a one-band approximation in which ${m}_{\mathrm{eff}}(\stackrel{\ensuremath{\rightarrow}}{r})$ is determined by the local value of the strain. The eight-band model predicts a lower ground-state energy and a larger number of excited states than the other approximations.

426 citations


Journal ArticleDOI
TL;DR: In this article, Monte Carlo simulations of electron transport based upon an analytical representation of the lowest conduction bands of bulk, wurtzite phase GaN are used to develop a set of transport parameters for devices with electron conduction in GaN.
Abstract: Monte Carlo simulations of electron transport based upon an analytical representation of the lowest conduction bands of bulk, wurtzite phase GaN are used to develop a set of transport parameters for devices with electron conduction in GaN. Analytic expressions for spherical, nonparabolic conduction band valleys at the Γ, U, M, and K symmetry points of the Brillouin zone are matched to experimental effective mass data and to a pseudopotential band structure. The low-field electron drift mobility is calculated for temperatures in the range of 300–600 K and for ionized impurity concentrations between 1016 and 1018 cm−3. Compensation effects on the mobility are also examined. Electron drift velocities for fields up to 500 kV/cm are calculated for the above temperature range. To aid GaN device modeling, the drift mobility dependences on ambient temperature, donor concentration, and compensation ratio are expressed in analytic form with parameters determined from the Monte Carlo results. Analytic forms are also...

326 citations


Journal ArticleDOI
TL;DR: In this article, the electronic band structures of wurtzite GaN and InN are calculated by the empirical pseudopotential method (EPM) with the form factors adjusted to reproduce band features which agree with recent experimental data and accurate first-principles calculations.
Abstract: The electronic band structures of wurtzite GaN and InN are calculated by the empirical pseudopotential method (EPM) with the form factors adjusted to reproduce band features which agree with recent experimental data and accurate first-principles calculations. The electron and hole effective masses at the Γ point are obtained using a parabolic line fit. Further, using the effective-mass Hamiltonian and the cubic approximation for wurtzite semiconductors, band edge dispersion at the Γ point obtained using the k.p method is fitted to that calculated using the EPM by adjusting the effective-mass parameters. Thus, we derived important band structure parameters such as the Luttinger-like parameters for GaN and InN which will be useful for material design in wide-gap nitride-based semiconductor lasers employing InGaN. The results also showed that the cubic approximation is fairly successful in the analysis of valence band structures for wurtzite nitrides.

274 citations


Journal ArticleDOI
TL;DR: In this article, a variational method was proposed to solve the Holstein model for an electron coupled to dynamical, quantum phonons on an infinite lattice, and the variational space can be systematically expanded to achieve high accuracy with modest computational resources.
Abstract: We describe a variational method to solve the Holstein model for an electron coupled to dynamical, quantum phonons on an infinite lattice. The variational space can be systematically expanded to achieve high accuracy with modest computational resources (12-digit accuracy for the 1d polaron energy at intermediate coupling). We compute ground and low-lying excited state properties of the model at continuous values of the wavevector $k$ in essentially all parameter regimes. Our results for the polaron energy band, effective mass and correlation functions compare favorably with those of other numerical techniques including DMRG, Global Local and exact diagonalization. We find a phase transition for the first excited state between a bound and unbound system of a polaron and an additional phonon excitation. The phase transition is also treated in strong coupling perturbation theory.

198 citations


Journal ArticleDOI
TL;DR: In this article, a model for the luminescence spectrum of silicon nanoclusters is presented, which is based on radiative recombination of confined excitons (quantum confinement).
Abstract: We present a model for the luminescence spectrum of silicon nanoclusters. We propose that the major contribution to luminescence is from radiative recombination of confined excitons (quantum confinement). Utilizing the effective mass approximation we consider the variation in oscillator strength with cluster size and the associated change in the number of available free carriers. By varying both the mean cluster size and size distribution of silicon nanoclusters, the luminescence spectra are modeled to a good fit. We compare our model with experimental photoluminescence and electroluminescence data from this group and from others.

192 citations


Journal ArticleDOI
TL;DR: In this paper, the pseudosite density matrix renormalization group (DMRG) was applied to the polaron problem in the one-and two-dimensional Holstein models.
Abstract: We propose a density-matrix renormalization-group (DMRG) approach to study lattices including bosons. The key to the approach is an exact mapping of a boson site containing ${2}^{N}$ states to $N$ pseudosites, each with 2 states. The pseudosites can be viewed as the binary digits of a boson level. We apply the pseudosite DMRG method to the polaron problem in the one- and two-dimensional Holstein models. Ground-state results are presented for a wide range of electron-phonon coupling strengths and phonon frequencies on lattices large enough (up to 80 sites in one dimension and up to $20\ifmmode\times\else\texttimes\fi{}20$ sites in two dimensions) to eliminate finite-size effects, with up to 128 phonon states per phonon mode. We find a smooth but quite abrupt crossover from a quasi-free-electron ground state with a slightly renormalized mass at weak electron-phonon coupling to a polaronic ground state with a large effective mass at strong coupling, in agreement with previous studies.

178 citations


Journal ArticleDOI
TL;DR: In this article, the band structure of CoSb sub-3 was analyzed and it was shown that the energy bands near the Fermi surface are typical of a narrow-band-gap semiconductor.
Abstract: We report calculations which show that the band structure of CoSb{sub 3} is typical of a narrow-band-gap semiconductor. The gap is strongly dependent on the relative position of the Sb atoms inside the unit cell. We obtain a band gap of 0.22 eV after minimization of these positions. This value is more than four times larger than the result of a previous calculation, which reported that the energy bands near the Fermi surface are unusual. The electronic states close to the Fermi level are properly described by a two-band Kane model. The calculated effective masses and band gap are in excellent agreement with Shubnikov{endash}de Haas and Hall effect measurements. Recent measurements of the transport coefficients of this compound can be understood assuming it is a narrow-band-gap semiconductor, in agreement with our results. {copyright} {ital 1998} {ital The American Physical Society}

173 citations


Journal ArticleDOI
TL;DR: In this paper, a model for doping-induced band edge displacements and band gap narrowing in both n-type and p-type 3C, 4H, and 6H-SiC was presented.
Abstract: Models for doping-induced band edge displacements and band gap narrowing in both n-type and p-type 3C–, 4H–, and 6H–SiC are presented for the first time. For comparison, Si has also been considered. The models constitute an extension of the theory of Jain and Roulston [Solid State Electron. 34, 453 (1991)] and take into account the three different electron effective mass components associated with hexagonal lattices. Furthermore, a more careful treatment of minority carrier correlation energy has been made, applying a two-band model for the dielectric function of a hole gas in the plasmon-pole approximation. The results for the band edge displacements are expressed in simple analytical form as functions of doping concentration.

133 citations


Journal ArticleDOI
TL;DR: In this paper, the binding energy of shallow hydrogenic impurities in spherical quantum dots with parabolic confinement was calculated, using a variational approach within the effective mass approximation, and the results showed that the impurity binding energy increases with the reduction in the dot dimension.
Abstract: The binding energy of shallow hydrogenic impurities in spherical quantum dots (QDs) with parabolic confinement is calculated, using a variational approach within the effective mass approximation. The binding energy is computed for GaAs QD as a function of the dot size for different impurity positions, and also as a function of the impurity position for different dot sizes. The results show that the impurity binding energy increases with the reduction in the dot dimension. The binding energy is also found to depend on the location of the impurity, and the same is the maximum for the on-center impurity.

131 citations


Journal ArticleDOI
TL;DR: In this paper, the size dependence of the electronic spectrum of InAs nanocrystals ranging in radius from 10 to 35 A has been studied by size-selective spectroscopy and an eight-band effective mass theory of the quantum size levels has been developed which describes the observed absorption level structure and transition intensities very well down to smallest crystal size using bulk band parameters.
Abstract: The size dependence of the electronic spectrum of InAs nanocrystals ranging in radius from 10–35 A has been studied by size-selective spectroscopy An eight-band effective mass theory of the quantum size levels has been developed which describes the observed absorption level structure and transition intensities very well down to smallest crystal size using bulk band parameters This model generalizes the six-band model which works well in CdSe nanocrystals and should adequately describe most direct semiconductor nanocrystals with band edge at the Γ-point of the Brillouin zone

130 citations


Journal ArticleDOI
TL;DR: In this article, the spin-orbit force in more general chiral effective field theories of nuclei is examined, with an emphasis on the role of the tensor coupling of the isoscalar vector meson (ω) to the nucleon.

Journal ArticleDOI
TL;DR: In this paper, the fine structure in the CdSe nanocrystal absorption spectrum is computed by incorporating two-particle electron-hole interactions and spin-orbit coupling into a tight-binding model, with an expansion in electronhole singleparticle states.
Abstract: The fine structure in the CdSe nanocrystal absorption spectrum is computed by incorporating two-particle electron-hole interactions and spin-orbit coupling into a tight-binding model, with an expansion in electron-hole single-particle states. The exchange interaction and spin-orbit coupling give rise to dark, low-lying states that are predominantly triplet in character, as well as to a manifold of exciton states that are sensitive to the nanocrystal shape. Near the band gap, the exciton degeneracies are in qualitative agreement with the effective mass approximation (EMA). However, instead of the infinite lifetimes for dark states characteristic of the EMA, we obtain finite radiative lifetimes for the dark states. In particular, for the lowest, predominantly triplet, states we obtain radiative lifetimes of microseconds, in qualitative agreement with the experimental measured lifetimes. The resonant Stokes shifts obtained from the splitting between the lowest dark and bright states are also in good agreement with experimental values for larger crystallites. Higher-lying states exhibit significantly more complex behavior than predicted by EMA, due to extensive mixing of electron-hole pair states.

Journal ArticleDOI
TL;DR: In this paper, an equation of motion with a velocity-dependent thermodynamic force is presented, and an expression for the effective mass of the dislocation that can be used in the equation is derived.
Abstract: The motion of dislocations at velocities approaching the speed of sound is considered. An equation of motion with a velocity-dependent thermodynamic force is presented. An expression for the effective mass of the dislocation that can be used in the equation of motion is derived. The expression for the effective mass reduces to the standard result in the low-velocity limit. Other possible choices for the effective mass are discussed.

Journal ArticleDOI
TL;DR: In this article, temperature and electric field-dependent electron transport in 3C, 4H, and 6H-SiC has been calculated by the Monte Carlo technique and it is found that ionized impurity scattering along with the deep donor ionization is responsible for the temperature dependence of mobility anisotropy ratio.
Abstract: Temperature- and electric field-dependent electron transport in 3C–, 4H–, and 6H–SiC has been calculated by the Monte Carlo technique. Due to the freezeout of deep donor levels the role of ionized impurity scattering in 6H–SiC is suppressed and the role of phonon scattering is enhanced, compared to 3C– and 4H–SiC. There are indications of impurity band formation for impurity concentrations exceeding 1019 cm−3. It is found that ionized impurity scattering along with the deep donor ionization is responsible for the temperature dependence of mobility anisotropy ratio. Electron effective masses and electron-phonon coupling constants have been deduced from the comparison of Monte Carlo simulation results with available experimental data on low-field electron mobility. The extracted model parameters are used for high-field electron transport simulations. The calculated velocity-field dependencies agree with experimental results. The saturation velocities in all three polytypes are close, but the transient veloc...


Journal ArticleDOI
TL;DR: In this paper, the electronic structure, charge distribution, effective charge, and charge transfer in ferroelectric tetragonal are carefully studied using a local density functional potential and a self-consistent ab initio LCAO (linear combination of atomic orbitals) method.
Abstract: The electronic structure, charge distribution, effective charge, and charge transfer in ferroelectric tetragonal are carefully studied using a local density functional potential and a self-consistent ab initio LCAO (linear combination of atomic orbitals) method. It is shown that the band gap and low-energy conduction band can be calculated with a reasonable accuracy when the ab initio LCAO method is used with an optimum basis set of atomic orbitals. The calculated optical spectrum, band gap, and effective mass of , obtained from the calculated electronic structure, are in good agreement with experimental results.

Journal ArticleDOI
TL;DR: In this paper, the magnetic circular dichroism of exciton states near the band edge of CdSe nanocrystallites (quantum dots) was investigated in the presence of an external magnetic field.
Abstract: We study the magnetic circular dichroism (MCD) of exciton states near the band edge of CdSe nanocrystallites (quantum dots) The experiment probes the difference between left and right circularly polarized transitions in the presence of an external magnetic field Analysis of the MCD signal determines the sign and magnitude of the exciton g-factor which is shown to be highly sensitive to the energy band parameters used in the effective mass approximation The observation of theoretically predicted changes in the sign of the exciton g-factor between the first two transitions is in agreement with recent theory describing the presence of fine structure underlying the optical transitions of CdSe nanocrystallites

Journal ArticleDOI
TL;DR: In this article, a model that describes grain-boundary-limited conduction in polycrystalline semiconductors, for thermally assisted ballistic as well as diffusive transport, both for degenerate and nondegenerate doping, is presented.
Abstract: We present a model that describes grain-boundary-limited conduction in polycrystalline semiconductors, for thermally assisted ballistic as well as diffusive transport, both for degenerate and nondegenerate doping. In addition to bulk parameters (the carrier effective mass and mean free path) the model contains grain boundary parameters (barrier height and width) and a coefficient of current nonuniformity. Temperature-dependent conductivity and Hall measurements on polycrystalline SnO2 thin films with different Sb concentrations are consistently interpreted.

Journal ArticleDOI
TL;DR: In this article, the wave functions obtained analytically at e = 0 decay linearly with the distance from the thicker nanotube, showing that the conductance decays with the junction length in proportion to its third power.
Abstract: Electronic states in junctions of nanotubes with different circumferences are studied in an effective-mass approximation. The junction is characterized by boundary conditions which mix wave functions associated with K and K' points. The wave functions obtained analytically at e = 0 decay linearly with the distance from the thicker nanotube, showing that the conductance decays with the junction length in proportion to its third power.

Journal ArticleDOI
TL;DR: In this article, a tunneling effective mass of 0.35m 0.60m 0 was derived for gate oxides by using multiple-scattering theory, in which the SiO2 layer is segmented into multiple rectangular potential barriers.
Abstract: Tunnel current through 1.27-8.12-nm-thick gate oxides has been calculated on the basis of multiple-scattering theory, in which the SiO2 layer is segmented into multiple rectangular potential barriers. By using the conduction band barrier height of 3.34 eV determined for the SiO2/Si(100) interfaces, a tunneling effective mass of 0.35m0 is obtained so as to reproduce the SiO2 thickness dependence on the direct tunnel current. The Fowler-Nordheim tunnel current oscillation due to interference between the propagating electron wave at the SiO2 conduction band and the wave reflected at the SiO2/Si interface has also been explained by employing an oxide conduction band effective mass of 0.60m0. It is found that the oxide thicknesses determined by ellipsometry are in good agreement with those extracted by fitting the measured tunnel current to theoretical one.

Journal ArticleDOI
TL;DR: In this article, two anomalous features were observed in the optical conductivity spectra of the intraband transition within the $3d$ band, which can be assigned to transitions involving the incoherent and coherent bands near the Fermi level.
Abstract: Optical conductivity spectra of single crystals of the perovskite-type ${3d}^{1}$ metallic alloy system ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{VO}}_{3}$ have been studied to elucidate how the electronic behavior depends on the strength of the electron correlation without changing the nominal number of electrons. The reflectivity measurements were made at room temperature between 0.05 eV and 40 eV. The effective mass deduced by the analysis of the Drude-like contribution to the optical conductivity and the plasma frequency do not show critical enhancement, even though the system is close to the Mott transition. Besides the Drude-like contribution, two anomalous features were observed in the optical conductivity spectra of the intraband transition within the $3d$ band. These features can be assigned to transitions involving the incoherent and coherent bands near the Fermi level. The large spectral weight redistribution in this system, however, does not involve a large mass enhancement.

Journal ArticleDOI
TL;DR: In this article, the integer quantum Hall effect is observed in two-dimensional electron gas at the AlGaN/GaN interface and a carrier effective mass of m*=0.228me is obtained.
Abstract: We have performed magnetotransport studies on AlGaN/GaN heterostructures at low temperature and magnetic field up to 30 T. The integer quantum Hall effect is observed in two-dimensional electron gas at the AlGaN/GaN interface. From the temperature dependence of the low-field Shubnikov–de Hass oscillations, a carrier effective mass of m*=0.228me is obtained. Dingle plots of our resistivity data show inhomogeneity in the two-dimensional electron gas. Finally, we found that for electronic density as high as 5.47×1012 cm−2, only the lowest subband in the quantum well is occupied.

Journal ArticleDOI
TL;DR: In this article, the degenerate temperature, scattering parameter, bandgap energy, and the effective masses of the electron and hole have been determined for SbI3 and CuBr-doped Bi2Te3-15% Bi2Se3 single crystals at temperatures ranging from 77 to 600 K.

Journal ArticleDOI
TL;DR: In this article, the problem of the density-dependent homogeneous broadening of microcavity polaritons due to exciton-exciton Coulomb interaction was addressed using the self-consistent Born approximation.
Abstract: The problem of the density-dependent homogeneous broadening of microcavity polaritons due to exciton-exciton Coulomb interaction is addressed using the self-consistent Born approximation. The theoretical results predict that, for resonant pumping of the lower polariton, the dependence of its broadening on the density of excitations has a threshold behavior. Below the threshold density, scattering is strongly inhibited because it involves only the small region of k space where the polariton effective mass is very light. Above threshold, the region of k space with excitonlike dispersion becomes allowed, giving the dominant contribution to the collision broadening. [S0163-1829(98)52740-3].

Journal ArticleDOI
TL;DR: In this paper, a technique for measuring the electrical resistivity and absolute thermopower of heavy fermions was presented for the case of CeRu2Ge2 and Yb-based compounds.
Abstract: A technique for measuring the electrical resistivity and absolute thermopower is presented for pressures up to 30 GPa, temperatures down to 25 mK and magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus on the interplay of normal phase and superconducting properties. With increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an antiferromagnetically ordered Kondo system to that characteristic of an intermediate valence compound as the Kondo temperature increases by about two orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a superconducting phase occurs which com- petes at low pressure with magnetic ordering. For CeCu2Si2 the effective mass of carriers is probed by both the coefficient of the Fermi liquid law and the ini- tial slope of the upper critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and Yb-based compounds for which pressure-induced magnetic ordering tends to develop. Finally, contrary to conventional wisdom, we argue that in heavy fermions a large part of the residual resistivity is most likely not independent of temperature; tentatively ascribed to Kondo hole, it can be very pressure as well as sample dependent. [electrical resistivity, thermoelectric power, heavy fermion, magnetic order, superconductivity]


Journal ArticleDOI
TL;DR: In this paper, the energy gap of CuIn3Se5 between 10 and 300 K was calculated using the model proposed by Elliot, which is compared to the semi-empirical relation suggested by Manoogian-Woolley.
Abstract: From the study of the temperature dependence of the optical absorption spectra, the energy gap EG of CuIn3Se5 between 10 and 300 K are calculated using the model proposed by Elliot. This variation is compared to the semiempirical relation suggested by Manoogian–Woolley. The Debye temperature ΘD, the dielectric constant e0, and the effective masses of free excitons mex, electrons me, and holes mh are estimated from the analysis of the adjustable parameters of these models.

Journal ArticleDOI
TL;DR: In this article, the Fermi surface and effective masses of electronic carriers in ferromagnetic EuB{sub 6} from pulsed field magnetization and steady field torque Landau quantum oscillatory measurements were determined.
Abstract: We have determined the Fermi surface and effective masses of electronic carriers in ferromagnetic EuB{sub 6} from pulsed field magnetization and steady field torque Landau quantum oscillatory measurements. To aid in the interpretation of the measurements, superconducting quantum interference device magnetometer measurements of the overall magnetization were made on the same samples. The results are consistent with recent electronic structure calculations and show both an electron and a hole pocket located at the {ital X} point in the Brillouin zone. {copyright} {ital 1998} {ital The American Physical Society}

Journal ArticleDOI
TL;DR: In this article, the role of the electric field on the binding energy of ground and first few excited states of a shallow impurity in a rectangular cross-sectional area vacuum/GaAs/vacuum quantum-well wire (QWW) was studied.
Abstract: We present a study of the role of the electric field on the binding energy of the ground and first few excited states of a shallow impurity in a rectangular cross-sectional area vacuum/GaAs/vacuum quantum-well wire (QWW), where the electric field is applied perpendicular to the symmetry axis of the wire. Using the effective-mass approximation within a variational scheme we calculate the binding energy of the 1s-like ground state as well as that of some excited states (2s-, 2px-, and 2pz-like) as a function of the geometry, applied electric field, and donor-impurity position. We found that the presence of the electric field breaks down the degeneracy of states for impurities symmetrically positioned within the structure, and that the geometric confinement and the electric field are determinant for the existence of bound excited states in these structures. Future interpretations of optical phenomena related with shallow donor impurities in vacuum/GaAs/vacuum QWWs, in which the effects of an applied electric...

Journal ArticleDOI
TL;DR: In this article, the authors show that the electric and magnetic radii of the bound nucleon are almost linearly correlated with the bag constant of the quark-meson coupling (QMC) model.