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Showing papers on "Effective mass (solid-state physics) published in 2002"


Journal ArticleDOI
13 Sep 2002-Science
TL;DR: These experiments demonstrate a strategy for probing the interrelation between geometric structure, elemental composition, and electronic properties in metallic nanostructures.
Abstract: The ability of a scanning tunneling microscope to manipulate single atoms is used to build well-defined gold chains on NiAl(110). The electronic properties of the one-dimensional chains are dominated by an unoccupied electron band, gradually developing from a single atomic orbital present in a gold atom. Spatially resolved conductance measurements along a 20-atom chain provide the dispersion relation, effective mass, and density of states of the free electron-like band. These experiments demonstrate a strategy for probing the interrelation between geometric structure, elemental composition, and electronic properties in metallic nanostructures.

376 citations


Journal ArticleDOI
TL;DR: In this article, infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy, and the results showed a pronounced increase in the electron effective mass with increasing electron concentration, indicating a nonparabolic conduction band in InN.
Abstract: Infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy. Measurements of the plasma edge frequencies were used to determine electron effective masses. The results show a pronounced increase in the electron effective mass with increasing electron concentration, indicating a nonparabolic conduction band in InN. We have also found a large Burstein-Moss shift of the fundamental band gap. The observed effects are quantitatively described by the kip interaction within the two-band Kane model of narrow-gap semiconductors.

370 citations


Journal ArticleDOI
TL;DR: In this paper, the band anticrossing model is extended over the entire Brillouin zone to explain the pressure behaviour of the lowest conduction band minimum in GaP1−xNx.
Abstract: In this paper we review the basic theoretical aspects as well as some important experimental results of the band anticrossing effects in highly electronegativity-mismatched semiconductor alloys, such as GaAs1−xNx and InyGa1−yAs1−xNx. The many-impurity Anderson model treated in the coherent potential approximation is applied to these semiconductor alloys, in which metallic anion atoms are partially substituted by a highly electronegative element at low concentrations. Analytical solutions of the Green's function provide dispersion relations and state broadenings for the restructured conduction bands. The solutions also lead to the physically intuitive and widely used two-level band anticrossing model. Significant experimental observations, including large bandgap reduction, great electron effective mass enhancement and unusual pressure behaviour of the bandgap, are compared with the predictions of the band anticrossing model. The band anticrossing model is extended over the entire Brillouin zone to explain the pressure behaviour of the lowest conduction band minimum in GaP1−xNx. Finally, we show that the band anticrossing can also account for the large bandgap bowing parameters observed in GaAsxSb1−x, InAsySb1−y and GaPxSb1−x alloys.

321 citations


Journal ArticleDOI
TL;DR: In this article, the energy spectrum of the bound states and their wave functions are explicitly written down and mapped the wave equation for these systems into well-known exactly solvable Schrodinger equations with constant mass using point canonical transformation.
Abstract: Given a spatially dependent mass distribution, we obtain potential functions for exactly solvable nonrelativistic problems. The energy spectrum of the bound states and their wave functions are written down explicitly. This is accomplished by mapping the wave equation for these systems into well-known exactly solvable Schrodinger equations with constant mass using point canonical transformation. The Oscillator, Coulomb, and Morse class of potentials are considered.

284 citations


Journal ArticleDOI
TL;DR: In this paper, an effective mass model was developed using particle-in-a-cylinder wave functions for electrons and holes to explore quantitatively the diameter-dependent photoluminescence (PL) data.
Abstract: Photoluminescence (PL) imaging and spectroscopy have been used to investigate isolated, individual indium phosphide nanowires (InP NWs) at both room temperature and 7 K PL images and spectra show that the emission maxima, line shapes, and intensities are nearly identical along the axis of a given NW PL spectra collected on InP NWs with diameters of 10, 15, 20, and 50 nm show that emission maxima systematically shift to higher energy with decreasing wire diameter, for diameters less than 20 nm An effective mass model (EMM) has been developed using particle-in-a-cylinder wave functions for electrons and holes to explore quantitatively the diameter-dependent PL data The EMM provides excellent fits to the diameter-dependent data obtained at both room temperature and 7 K, and shows that the shifts in the emission spectra can be explained by radial quantum confinement

244 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of crystal orientation on the electronic properties of wurtzite InGaN/GaN quantum wells with piezoelectric (PZ) and spontaneous (SP) polarization was investigated using the multiband effective-mass theory.
Abstract: Crystal orientation effects on electronic properties of wurtzite InGaN/GaN quantum wells (QWs) with piezoelectric (PZ) and spontaneous (SP) polarization are investigated using the multiband effective-mass theory. With increasing crystal angle, the internal field of the InGaN/GaN QW structure changes its sign near the crystal angle of 55° while that of the GaN/AlGaN QW structure gradually decreases without changing its sign. The interband transition energy is redshifted for crystal angles near θ=0° and gradually increases with the crystal angle due to the reduced SP and PZ polarization effects. The y′-polarized optical matrix element largely increases with increasing crystal angle. This is mainly due to the fact that the states constituting the topmost valence subband near the band edge are predominantly |Y′〉-like for QW structures with larger crystal angle. Also, it is observed that the average hole effective mass is largely reduced with increasing crystal angle. In particular, the average hole effective ...

209 citations


Journal ArticleDOI
TL;DR: In this paper, single-phase spinel zinc stannate (Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates.
Abstract: Single-phase, spinel zinc stannate (Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10−2–10−3 Ω cm, mobilities of 16–26 cm2/V s, and n-type carrier concentrations in the low 1019 cm−3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. 119Sn Mossbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn+4. A pronounced Burstein–Moss shift moved the optical band gap from 3.35 to as high as 3.89 eV. Density-of-states effective mass, relaxation time, mobility, Fermi energy level, and a scattering parameter were calculated from resistivity, Hall, Seebeck, and Nernst coefficient transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 me as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. A bottom-of-the-band ...

199 citations


Journal ArticleDOI
TL;DR: In this paper, the Shubnikov-de Haas (SdH) oscillations in highmobility Si-MOS samples over a wide range of carrier densities n approximately (1-50)x10(11) cm(-2), which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT).
Abstract: We studied the Shubnikov-de Haas (SdH) oscillations in high-mobility Si-MOS samples over a wide range of carrier densities n approximately (1-50)x10(11) cm(-2), which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT). Using a novel technique of measuring the SdH oscillations in superimposed and independently controlled parallel and perpendicular magnetic fields, we determined the spin susceptibility chi(*), the effective mass m(*), and the g(*) factor for mobile electrons. These quantities increase gradually with decreasing density; near the 2D MIT, we observed enhancement of chi(*) by a factor of approximately 4.7.

166 citations


Journal ArticleDOI
TL;DR: In this article, the superconductivity of the filled skutterudite compound PrOs 4 Sb 12 has been investigated, with a critical temperature T c ≈ 1.85 K, that appears to involve heavy fermion quasiparticles with an effective mass m * ≈10 2 m e, where m e is the free electron mass.
Abstract: The filled skutterudite compound PrOs 4 Sb 12 exhibits superconductivity, with a superconducting critical temperature T c ≈1.85 K, that appears to involve heavy fermion quasiparticles with an effective mass m * ≈10 2 m e , where m e is the free electron mass. Evidence for the heavy fermion state in PrOs 4 Sb 12 based on electrical resistivity, specific heat, and magnetic susceptibility measurements in the normal and superconducting states, is reviewed. New measurements are presented that reveal that T c decreases linearly with pressure to ∼20 kbar, the normal state resistivity decreases with decreasing temperature below ∼1-2 K as a power law T n with n ∼3-2.6 in magnetic fields from 30 to 80 kOe, and there is structure in the specific heat jump at T c , suggesting that there are two distinct superconducting phases. Inelastic neutron scattering measurements are consistent with a Pr 3+ energy level scheme in the cubic crystalline electric field with a Γ 3 nonmagnetic doublet ground state that carries an ele...

157 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that at intermediate temperatures, the metallic temperature dependence of the conductivity σ(T) of two-dimensional electrons in silicon is described well by a recent interaction-based theory of Zala et al.
Abstract: We find that at intermediate temperatures, the metallic temperature dependence of the conductivity σ(T) of two-dimensional electrons in silicon is described well by a recent interaction-based theory of Zala et al. [Phys. Rev. B 64, 214204 (2001)]. The tendency of the slope σ - 1 dσ/dT to diverge near the critical electron density is in agreement with the previously suggested ferromagnetic instability in this electron system. Comparing theory and experiment, we arrive at a conclusion that the instability, unexpectedly, originates from the sharp enhancement of the effective mass, while the effective Lande g factor remains nearly constant and close to its value in bulk silicon.

155 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss the relationship between exact solvability of the Schrodinger equation with a position-dependent mass and the ordering ambiguity in the Hamiltonian operator within the framework of supersymmetric quantum mechanics.
Abstract: We discuss the relationship between exact solvability of the Schrodinger equation with a position-dependent mass and the ordering ambiguity in the Hamiltonian operator within the framework of supersymmetric quantum mechanics. The one-dimensional Schrodinger equation, derived from the general form of the effective mass Hamiltonian, is solved exactly for a system with exponentially changing mass in the presence of a potential with similar behaviour, and the corresponding supersymmetric partner Hamiltonians are related to the effective-mass Hamiltonians proposed in the literature.

Journal ArticleDOI
TL;DR: In this paper, the de Haas-van Alphen effect was investigated in the Pr-based heavy fermion superconductor PrOs$_4$Sb$12}.
Abstract: We have investigated the de Haas-van Alphen effect in the Pr-based heavy fermion superconductor PrOs$_4$Sb$_{12}$.The topology of Fermi surface is close to the reference compound LaOs$_4$Sb$_{12}$ and well explained by the band structure calculation based on the FLAPW-LDA+U method, where the 4{\it f} electrons are localized. We have confirmed a highly enhanced cyclotron effective mass 2.4$\sim7.6m_{\rm 0}$ which is apparently large compared to the usual Pr-based compounds.

Journal ArticleDOI
01 Apr 2002
TL;DR: In this paper, the authors consider the role of 0.04-eV phonons in both the luminescence excitation and emission processes of feldspar sediments at elevated temperatures.
Abstract: Most natural feldspars contain many charged impurities, and display a range of bond angles, distributed about the ideal. These effects can lead to complications in the structure of the conduction band, giving rise to a tail of energy states (below the high-mobility conduction band) through which electrons can travel, but with reduced mobility: transport through these states is expected to be thermally activated. The purpose of this article is twofold. Firstly, we consider what kind of lattice perturbations could give rise to both localized and extended conduction band-tail states. Secondly, we consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04–0.05-eV phonons play in both the luminescence excitation and emission processes of these materials. It also has relevance in the dating of feldspar sediments at elevated temperatures.

Journal ArticleDOI
TL;DR: In this article, the effects of meson exchange on the three-body force were investigated up to high baryonic density and it was found that the major role is played by the competition between the strongly repulsive (σ,ω)-exchange term with virtual nucleon-antinucleon excitation and the large attractive contribution due to N ∗ (1440) resonance excitation.

Journal ArticleDOI
TL;DR: In this paper, a general method for obtaining exact solutions of Schrodinger equations with a position-dependent effective mass was proposed and compared with those obtained within the frame of supersymmetric quantum theory, where the distinct effective mass Hamiltonians proposed in the literature in fact describe exactly equivalent systems having identical spectra and wave functions as far as exact solvability is concerned.
Abstract: We outline a general method for obtaining exact solutions of Schrodinger equations with a position-dependent effective mass and compare the results with those obtained within the frame of supersymmetric quantum theory. We observe that the distinct effective mass Hamiltonians proposed in the literature in fact describe exactly equivalent systems having identical spectra and wave functions as far as exact solvability is concerned. This observation clarifies the Hamiltonian dependence of the band-offset ratio for quantum wells.

Journal ArticleDOI
TL;DR: From experimental observations of limiting temperatures in heavy ion collisions and theoretical model correlations, the critical temperature of infinite nuclear matter Tc is derived and a value of K in moderately excited nuclei is indicated that is in excellent agreement with the value determined from giant monopole resonance data.
Abstract: From experimental observations of limiting temperatures in heavy ion collisions we derive the critical temperature of infinite nuclear matter T c = 16.6′0.86. Theoretical model correlations between T c , the compressibility modulus K, the effective mass m*, and the saturation density ρ s are then exploited to derive the quantity (K/m*) 1 / 2 ρ s -1/3. This quantity together with calculations employing Skyrme and Gogny interactions indicates a value of K in moderately excited nuclei that is in excellent agreement with the value determined from giant monopole resonance data.

Journal ArticleDOI
TL;DR: In this article, the ground state energy of the Holstein polaron has been investigated on an infinite lattice in D dimensions, where the computational method converges as a power law, so that highly accurate results can be achieved with modest resources.
Abstract: Based on a recently developed variational method, we explore the properties of the Holstein polaron on an infinite lattice in D dimensions, where $1l~Dl~4.$ The computational method converges as a power law, so that highly accurate results can be achieved with modest resources. We present the most accurate ground state energy (with no small parameter) to date for polaron problems, 21 digits for the one-dimensional (1D) polaron at intermediate coupling. The dimensionality effects on polaron band dispersion, effective mass, and electron-phonon (el-ph) correlation functions are investigated in all coupling regimes. It is found that the crossover to large effective mass of the higher-dimensional polaron is much sharper than the 1D polaron. The correlation length between the electron and phonons decreases significantly as the dimension increases. Our results compare favorably with those of the quantum Monte Carlo, dynamical mean-field theory, density-matrix renormalization-group, and Toyozawa variational methods. We demonstrate that the Toyozawa wave function is qualitatively correct for the ground-state energy and the two-point electron-phonon correlation functions, but fails for the three-point functions. Based on this finding, we propose an improved Toyozawa variational wave function.

Journal ArticleDOI
TL;DR: In this article, the competition between the Kondo effect and frustrating exchange interactions in a Kondo-lattice model within a large-cal N$ dynamical mean-field theory was studied.
Abstract: We study the competition between the Kondo effect and frustrating exchange interactions in a Kondo-lattice model within a large-${\cal N}$ dynamical mean-field theory. We find a T=0 phase transition between a heavy Fermi-liquid and a spin-liquid for a critical value of the exchange $J_c = T_{K}^0$, the single-impurity Kondo temperature. Close to the critical point, the Fermi liquid coherence scale $T^\star$ is strongly reduced and the effective mass strongly enhanced. The regime $T>T^\star$ is characterized by spin-liquid magnetic correlations and non-Fermi-liquid properties. It is suggested that magnetic frustration is a general mechanism which is essential to explain the large effective mass of some metallic compounds such as LiV$_2$O$_4$.

Journal ArticleDOI
TL;DR: In this paper, a general method for obtaining exact solutions of Schr\"{o}dinger equations with a position dependent effective mass was proposed and compared with those obtained within the frame of supersymmetric quantum theory.
Abstract: We outline a general method for obtaining exact solutions of Schr\"{o}dinger equations with a position dependent effective mass and compare the results with those obtained within the frame of supersymmetric quantum theory. We observe that the distinct effective mass Hamiltonians proposed in the literature in fact describe exactly equivalent systems having identical spectra and wave functions as far as exact solvability is concerned. This observation clarifies the Hamiltonian dependence of the band-offset ratio for quantum wells.

Journal ArticleDOI
TL;DR: In this article, a parametric self-consistency method utilizing the triangular well approximation is used for the electrostatics of the inversion layer of metal-oxide-semiconductor field effect transistors.
Abstract: We present a physical model to calculate the direct tunneling hole current through ultrathin gate oxides from the inversion layer of metal–oxide–semiconductor field-effect transistors. A parametric self-consistency method utilizing the triangular well approximation is used for the electrostatics of the inversion layer. For hole quantization in the inversion layer, an improved one-band effective mass approximation, which is a good approximation to the rigorous six-band effective mass theory, is used to account for the band-mixing effect. The tunneling probability is calculated by a modified Wentzel–Kramers–Brilliouin (WKB) approximation, which takes the reflections near the Si/SiO2 interfaces into account. It is found that the parabolic dispersion in the SiO2 band gap used in the WKB approximation is only applicable for hole tunneling in oxides thinner than about 2 nm and for low gate voltage. A more reasonable Freeman–Dahlke hole dispersion form with significantly improved fitting to all experimental data...

Journal ArticleDOI
TL;DR: The hydrodynamic equations of superfluids for a weakly interacting Bose gas are generalized to include the effects of periodic optical potentials produced by stationary laser beams to make predictions for the frequencies of the collective modes of a condensate confined by a magnetic harmonic trap.
Abstract: The hydrodynamic equations of superfluids for a weakly interacting Bose gas are generalized to include the effects of periodic optical potentials produced by stationary laser beams. The new equations are characterized by a renormalized interaction coupling constant and by an effective mass accounting for the inertia of the system along the laser direction. For large laser intensities the effective mass is directly related to the tunneling rate between two consecutive wells. The predictions for the frequencies of the collective modes of a condensate confined by a magnetic harmonic trap are discussed for both 1D and 2D optical lattices and compared with recent experimental data.

Journal ArticleDOI
TL;DR: In this paper, a comprehensive review of nitrogen-induced modifications of the electronic structure of Ga1−yInyNxAs1−x alloys is carried out, and the results are analyzed in terms of the analytical band anti-crossing model as well as the local density approximation calculations and empirical pseudopotential models.
Abstract: In this paper, we carry out a comprehensive review of the nitrogen-induced modifications of the electronic structure of Ga1−yInyNxAs1−x alloys. We study in detail the behaviour of the conduction-band effective mass as a function of Fermi energy, nitrogen content and pressure. From measurements of the plasma frequency for samples with different electron concentrations we have determined the dispersion relation for the lowest conduction band. We have also studied composition, temperature and pressure dependent optical absorption spectra on free-standing layers of Ga1−yInyNxAs1−x (0 ≤ x ≤ 0.025 and 0 ≤ y ≤ 0.09) lattice-matched to GaAs. Spectroscopic ellipsometry measurements performed in a wide photon energy range from 1.5 to 5.5 eV have been used to determine the energy dependence of the dielectric function as well as the energies of E1, E0' and E2 critical point transitions. Experiments have shown that nitrogen has a large effect on the dispersion relations and on the optical spectra for the conduction-band states close to the Γ point. A much smaller effect has been observed for X and L minima as well as for the valence-band states. We have compared our results with other available experimental data. The results are analysed in terms of the analytical band anti-crossing model as well as the local density approximation calculations and empirical pseudopotential models.

Journal ArticleDOI
TL;DR: In this paper, the radial extent of the electron wave functions in the ground and excited states was investigated for Feldspar materials and it was shown that under low-energy optical stimulation (hν∼ 1.4 eV), luminescence can be a competitive process between direct electron-hole tunnelling recombination and free-to-bound recombination.
Abstract: The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states. It is shown that for NaAlSi3O8, the ground-state wavefunction is expected to be confined well within a single lattice unit cell, but the first excited state is far more extensive, being spread over several unit cells. This aspect is of direct relevance to understanding the nature of various luminescence processes in the materials. Under low-energy optical stimulation (hν∼ 1.4 eV), luminescence can be a competitive process between direct electron-hole tunnelling recombination (with the charge still trapped at the defect sites), and free-to-bound recombination (after the excited state electron accesses the conduction band). We show that analysis of the thermal behaviour of the luminescence can be used to separate the two processes.

Journal ArticleDOI
TL;DR: The doping and temperature dependence of the complex conductivity is determined for the ferromagnetic semiconductor Ga(1-x)Mn(x)As and a significant decrease in the effective mass is observed, demonstrating the role played by the heavy carriers in inducing ferromagnetism in this system.
Abstract: The doping and temperature dependence of the complex conductivity is determined for the ferromagnetic semiconductor Ga1� xMnxAs. A broad resonance develops with Mn doping at an energy scale of � 200 meV, well within the GaAs band gap. Possible origins of this feature are explored in the context of a Mn induced impurity band and intervalence band transitions. From a sum rule analysis of the conductivity data the effective mass of the itinerant charge carriers is found to be at least a factor of 3 greater than what is expected for hole doped GaAs. In the ferromagnetic state a significant decrease in the effective mass is observed, demonstrating the role played by the heavy carriers in inducing ferromagnetism in this system.

Journal ArticleDOI
TL;DR: In this paper, the conductivity effective masses of electrons and holes in Si were calculated for carrier temperatures from 1 to 3000 K. The temperature dependence of the electron mass was calculated by use of a phenomenological model of conduction-band nonparabolicity that has been fitted to experimental measurements.
Abstract: The conductivity effective masses of electrons and holes in Si are calculated for carrier temperatures from 1 to 3000 K. The temperature dependence of the electron mass is calculated by use of a phenomenological model of conduction-band nonparabolicity that has been fitted to experimental measurements of the dependence of the electron conductivity effective mass on carrier concentration. The hole mass is investigated by tight-binding calculations of the valence bands, which have been adjusted to match experimental values of the valence-band curvature parameters at the top of the valence band. The calculations are in excellent agreement with femtosecond-laser reflectivity measurements of the change in optical effective mass as hot carriers cool from 1550 to 300 K.

Journal ArticleDOI
TL;DR: Observations of quantum oscillations in single crystals of the high temperature superconductor MgB2 are reported, and it is found that the electron-phonon coupling strength lambda is a factor of approximately 3 larger for the c-axis tube orbits than for the in-plane network orbit, in accord with recent microscopic calculations.
Abstract: We report observations of quantum oscillations in single crystals of the high temperature superconductor ${\mathrm{MgB}}_{2}$. Three de Haas\char21{}van Alphen frequencies are clearly resolved. Comparison with band structure calculations strongly suggests that two of these come from a single warped Fermi surface tube along the $c$ direction, and that the third arises from cylindrical sections of an in-plane honeycomb network. The measured values of the effective mass range from $(0.44\char21{}0.68){m}_{e}$. By comparing these to calculated band masses, we find that the electron-phonon coupling strength $\ensuremath{\lambda}$ is a factor of $\ensuremath{\sim}3$ larger for the $c$-axis tube orbits than for the in-plane network orbit, in accord with recent microscopic calculations.

Journal ArticleDOI
TL;DR: In this paper, the influence of external electric field and hydrostatic stress on the binding energy and impurity polarizability of shallow-donor impurities in an isolated GaAs-(Ga, Al)As quantum well is considered.
Abstract: Theoretical calculations on the influence of both an external electric field and hydrostatic stress on the binding energy and impurity polarizability of shallow-donor impurities in an isolated GaAs-(Ga, Al)As quantum well are presented. A variational procedure within the effective-mass approximation is considered. The pressure-related Γ-X crossover is taken into account. As a general feature, we observe that the binding energy increases as the length of the well decreases. For the low-pressure regime we observe a linearly binding energy behaviour. For the high-pressure regime the simultaneous effects of the barrier height and the applied electric field bend the binding energy curves towards smaller values. For low hydrostatic pressures the impurity polarization remains constant in all cases with an increasing value as the field increases. This constant behaviour shows that the small variations in well width, effective mass, and dielectric constant with pressure do not appreciably affect polarizability. For high hydrostatic pressure, we see a non-linear increase in polarizability, mainly due to the decrease of barrier height as a result of the external pressure, which allows further deformation of the impurity.

Journal ArticleDOI
01 Aug 2002
TL;DR: In this article, the complex-band structure of a molecular wire leads to an analytical expression for the effective mass m* of a tunneling electron through this wire, compared to the ones of standard solid state tunnel junction.
Abstract: Observed from the electrodes, the electronic tunnel transport regime though a molecular wire is described by a generalized non-parabolic dispersion relationship. The calculation of the complex-band structure of a molecular wire leads to an analytical expression for the effective mass m* of a tunneling electron through this wire. m* is calculated for different molecular wires and compared to the ones of standard solid state tunnel junction. In the tunneling regime, the conductance optimization of a molecular wire depends equally on this m* and on its homo–lumo gap.

Journal ArticleDOI
TL;DR: In this article, a simple analytical method for calculating the strain distribution in and around self-assembled (In,Ga)As/GaAs quantum-dot nanostructures is presented.
Abstract: This paper presents a simple analytical method for calculating the strain distribution in and around self-assembled (In,Ga)As/GaAs quantum-dot nanostructures. The dots are assumed to be buried in an infinite medium so that the effects of free surfaces can be neglected. This assumption is based on the relative size of the dot, compared to that of the overlayer. The model—based on classical continuum elasticity—is capable of handling dots of arbitrary shapes; here, however, only dots with pyramidal and truncated-pyramidal shapes are considered. The approximate shape of the dots is extracted from high-resolution transmission electron microscope observations. The electronic energy levels in the dots are calculated by solving the three-dimensional effective mass Schrodinger equation. The carrier confinement potential in this equation is modified by the strain distribution. Because the dots are in a strong confinement regime, the effects of Coulomb interactions are neglected. The calculated confined eigen-energies agree with our experimental photoluminescence data. The calculations also support previous results reported by others.

Journal ArticleDOI
TL;DR: In this article, the authors performed band structure calculations for the low-temperature modifications of the silver chalcogenides β-Ag 2 Se, β -Ag 2 Te and the ternary compound δ-Ag 3 AuSe 2 by the local spherical wave (LSW) method.