Showing papers on "Effective mass (solid-state physics) published in 1994"
TL;DR: In this article, a variational method is used to calculate the deflection and the fundamental and harmonic resonance frequencies of commercial V•shaped and rectangular atomic force microscopy cantilevers, which is roughly half that calculated for the equivalent rectangular cantilever.
Abstract: A variational method is used to calculate the deflection and the fundamental and harmonic resonance frequencies of commercial V‐shaped and rectangular atomic force microscopy cantilevers. The effective mass of V‐shaped cantilevers is roughly half that calculated for the equivalent rectangular cantilevers. Damping by environmental gases, including air, nitrogen, argon, and helium, affects the frequency of maximum response and to a much greater degree the quality factor Q. Helium has the lowest viscosity, resulting in the highest Q, and thus provides the best sensitivity in noncontact force microscopy. Damping in liquids is dominated by an increase in effective mass of the cantilever due to an added mass of the liquid being dragged with that cantilever.
293 citations
TL;DR: In this article, the van der Pauw method was used to measure the hole concentration and Hall mobility in Mg•doped GaN and Al0.08Ga0.92N.
Abstract: Temperature dependences of the hole concentration and Hall mobility in Mg‐doped GaN and Al0.08Ga0.92N grown by metalorganic vapor phase epitaxy were measured by the van der Pauw method over a wide temperature range from 100 to 500 K. Assuming that the effective mass of holes in Al0.08Ga0.92N is equal to that of GaN, the activation energy of the Mg shallow acceptor in Al0.08Ga0.92N is estimated to be about 35 meV deeper than that in GaN.
248 citations
TL;DR: In this paper, a detailed effective mass calculation of the energy levels in InAs quantum dots embedded in GaAs is presented, and the results of a separable approximate treatment with a more complete numerical approach are compared.
166 citations
TL;DR: In this article, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO2 barrier into the metal is made.
Abstract: Ultrathin oxide layers, 2– nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (RTO) at 900°C. RTO is an effective method to control the oxide thickness in this range to within 10%. The direct tunnelling through these ultrathin layers is examined with current-voltage and impedance measurements on Al/SiO2/n-Si structures with an oxide layer thickness between 2 and 4 nm. After the determination of the surface potential vs bias relation and the oxide layer capacitance from the capacitance-voltage measurements, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO2 barrier into the metal is made. A very good agreement with the theory is obtained assuming a simple trapezoidal tunnel barrier for the SiO2, from which the tunnel barrier height and the electron effective mass in the SiO2 bandgap are derived. The density of interface traps at the Si/SiO2 interface is determined using the conductance method. Only a very small increase of interface trap density with decreasing oxide layer thickness is found. The very high density of interface traps (more than 3 × 1012 cm−2 eV−1) can be reduced to the 1010 cm−2 eV−1 level by application of a conventional Post Metallization Anneal (PMA).
136 citations
TL;DR: In this article, a simplified model of the band structure of kappa -(BEDT-TTF)2Cu(NCS)2 has been used to derive the bare band masses of the electrons from optical data.
Abstract: Magnetotransport measurements have been carried out on the organic superconductor kappa -(BEDT-TTF)2Cu(NCS)2 at temperatures down to 500 mK and in hydrostatic pressures up to 16.3 kbar. The observation of Shubnikov-de Haas and magnetic breakdown oscillations has allowed the pressure dependences of the area of the closed pocket of the Fermi surface and the carrier effective masses to be deduced and compared with simultaneous measurements of the superconducting critical temperature Tc. The effective mass measured by the temperature dependence of the Shubnikov-de Haas oscillations is found to fall rapidly with increasing pressure up to a critical pressure Pc approximately=5 kbar. Above Pc a much weaker pressure dependence is observed; Tc also falls rapidly with pressure from 10.4 K at ambient pressure to zero at around Pc. This strongly suggests that the enhanced effective mass and the superconducting behaviour are directly connected in this organic superconductor. A simplified model of the band structure of kappa -(BEDT-TTF)2Cu(NCS)2 has been used to derive the bare band masses of the electrons from optical data. Comparisons of these parameters with cyclotron resonance data and the effective masses measured in the present experiments indicate that the greater part of the enhancement of the effective mass necessary for superconductivity in this material is due to quasiparticle interactions, with the electron-phonon interactions playing a secondary role. The dependence of Tc on the effective mass may be fitted satisfactorily to a suitably parametrized weak-coupling BCS expression, although this cannot be taken as a definitive proof of the nature of superconductivity in organic conductors.
126 citations
TL;DR: In this paper, the Harrison model was used to describe the band lineups of InGaAlAs on (001) InP as well as InGaAsP on (1, 2)-InP system with strain effects.
Abstract: We describe the band lineups of InGaAlAs on (001) InP as well as InGaAsP on (001) InP system with strain effects, based on the Harrison model. We show that the compressive strain does not affect the band position so much, and tensile strain raises the band position in the InGaAsP system. It is also shown that both compressive and tensile strains raise the band positions in the InGaAlAs system. The conduction and valence band positions of InGaAs, InGaAsP, and InGaAlAs relative to InP valence band are given in approximate formulas as a function of the strain. We calculate the energy versus in-plane wave vector relationship of the InGaAsP/InGaAs(P) InGaAlAs/InGa(Al)As on InP strained quantum-well systems. We obtain the in-plane effective mass of the strained quantum-well system by fitting the dispersion relationship to a parabolic curve. The in-plane effective masses of several kinds of strained quantum-well systems are listed. >
115 citations
106 citations
TL;DR: The calculated energy dependence of the transition lifetimes is too strong to explain the observed low-energy slow emission band in porous Si purely in terms of transitions in an ideal wire, however, an alternative model, which introduces a mixture of wires and boxes, can account for the experimental slope.
Abstract: We have used the empirical pseudopotential method to study the electronic and optical properties of [001] Si quantum wires with (110)--([bar 1]10) square cross sections ranging from 4[times]4 to 14[times]14 monolayers (7.7[times]7.7 to 26.9[times]26.9 A, respectively). We present energy levels, band gaps, oscillator-strength, and charge-density distributions. To understand the electronic structure of these systems we calculate their properties in a stepwise process, considering (1) wires with a free surface but without hydrogen and (2) wires with hydrogen chemisorption on the surface. We find that (i) in both cases, the band gap between bulklike states increases as the wire size is reduced (due to quantum confinement). However, (ii) hydrogen chemisorption acts to reduce the gap. (iii) Whereas the low-energy states near the valence-band [ital minimum] are effective-mass-like, the near-band-gap states with or without H on the surface can be decisively non-effective-mass-like. The lowest conduction states are pseudodirect, not direct. (iv) The calculated energy dependence of the transition lifetimes is too strong to explain the observed low-energy slow'' emission band in porous Si purely in terms of transitions in an ideal wire. However, an alternative model, which introduces a mixture of wires and boxes, can account for the experimental slope.
104 citations
TL;DR: Strain Hamiltonian and k⋅p theory are employed to calculate low-field hole mobility of strained Si layers on (100)Si1−xGex substrate as discussed by the authors.
Abstract: Strain Hamiltonian and k⋅p theory are employed to calculate low‐field hole mobility of strained Si layers on (100)Si1−xGex substrate. Nonparabolicity and the warped nature of the valence bands are included. At room temperature, in‐plane hole mobilities of strained Si are found to be 1103 and 2747 cm 2 V−1 s−1 for x equal to 0.1 and 0.2, respectively. These hole mobilities are, respectively, 2.4 and 6 times higher than that of bulk Si. This improvement in the mobility results is mainly due to the large splitting energy between the occupied light‐hole band and the empty heavy‐hole band and smaller effective mass. The effect of p‐type doping on mobility is also presented.
93 citations
TL;DR: This work calculates the effective mass of the [omega] meson in nuclear matter in a relativistic random-phase approximation to the Walecka model and reports a reduction in the meson mass of about 170 MeV at nuclear-matter saturation density.
Abstract: We calculate the effective mass of the [omega] meson in nuclear matter in a relativistic random-phase approximation to the Walecka model. The dressing of the meson propagator is driven by its coupling to particle-hole pairs and nucleon-antinucleon ([ital N[bar N]]) excitations. We report a reduction in the [omega]-meson mass of about 170 MeV at nuclear-matter saturation density. This reduction arises from a competition between the density-dependent (particle-hole) dressing of the propagator and vacuum polarization ([ital N[bar N]] pairs). While density-dependent effects lead to an increase in the mass proportional to the classical plasma frequency, vacuum polarization leads to an even larger reduction caused by the reduced effective nucleon mass in the medium.
84 citations
TL;DR: In this article, the first observation of cyclotron resonance in 6H-SiC by ODCR spectroscopy at X-band microwave frequency is reported. And the anisotropy of the effective mass and the carrier mobility is discussed in comparison with previously reported data.
Abstract: The first observation of cyclotron resonance in 6H‐SiC by optically detected cyclotron resonance (ODCR) spectroscopy at X‐band microwave frequency is reported. High purity undoped, n‐type 6H‐SiC layers grown by chemical vapor deposition (CVD), with residual doping concentrations in the 1014–1015 cm−3 range, were investigated. Effective mass values were determined as m*⊥=(0.42±0.02)m0 and m*∥=(2.0±0.2)m0. From the fit of the ODCR line shape, a remarkably high mobility at 6 K was deduced: μ⊥≊1.1×105 cm2/V s for electrons in the basal plane. The anisotropy of the effective mass and the carrier mobility is discussed in comparison with previously reported data.
TL;DR: In this paper, the vibrational modes of inertial polarization in the multilayer wire-like and dot-like structures are determined and the bulk confinement modes and the interface modes are separated exactly by a unitary transformation, various additional boundary conditions for the inertial polarisation vector being taken into account.
Abstract: The vibrational modes of inertial polarization in the multilayer wire-like and dot-like structures are determined. The bulk confinement modes and the interface ones are separated exactly by a unitary transformation, various additional boundary conditions for the inertial polarization vector being taken into account. The Hamiltonian of the electron-phonon interaction is deduced. The polaron ground state energy as well as the effective mass in the cylindrical quantum wire and polaronic shift of electron energy levels in the spherical quantum dot are calculated.
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TL;DR: In this article, the relativistic mean field model was used to study the properties of antikaons and kaons in dense nuclear matter, and it was shown that antikaon condensation may occur in chiral models, only for relatively high values of the nucleon effective mass, m N ∗ /m N > 0.75, and does not occur in models based on one boson exchange underlying K N interactions.
TL;DR: In this paper, the dc Josephson effect of a superconductor/two-dimensional electron gas/superconductor (S/2DEG/S junction in the clean limit) was investigated with emphasis on the field-effect dependence of the critical current.
Abstract: The dc Josephson effect of a superconductor/two-dimensional electron gas/superconductor (S/2DEG/S junction in the clean limit is investigated with emphasis on the field-effect dependence of the critical current. Calculation of the Josephson current is based on solving the Bogoliubov--de Gennes equations for a steplike variation of the pair potential. In the normal conducting region, the motion of electrons is quantized in one direction by means of a triangular-well potential. The 2DEG is contained in a semiconductor treated within the effective-mass approximation. We assume an abrupt band-edge jump at the interfaces, and additional scattering is taken into account by \ensuremath{\delta}-function potential barriers. Normal scattering leads to the formation of resonant states, which are visible in critical current oscillations. The ratio of Fermi velocities in the 2DEG and the S regions determines the rates of Andreev and normal scattering and has a large influence on the field-effect dependence of the critical current. We take an effective mass suitable for the inversion layer on p-type InAs and consider Nb for the superconducting contacts. Typical magnitudes of the calculated critical current are some \ensuremath{\mu}A-per-\ensuremath{\mu}m junction width for experimentally accessible values of junction length, temperature, and surface carrier density of the 2DEG.
TL;DR: It is found indication that the larger initial lepton fraction thus obtained may significantly help the subsequent supernova explosion.
Abstract: The temperature dependence of the nucleon effective mass is calculated for the $^{98}\mathrm{Mo}$, $^{64}\mathrm{Zn}$, and $^{64}\mathrm{Ni}$. In all three cases, the effective mass is found to decrease appreciably in the temperature interval 0--1 MeV. Such a dependence has consequences, among other things, on the level-density parameter and on the symmetry energy. In particular, the effect of the increased symmetry energy on the neutronization processes in collapsing stars is estimated. We find indication that the larger initial lepton fraction thus obtained may significantly help the subsequent supernova explosion.
TL;DR: In this paper, an analytic model for the valence-subband structure in a compressively strained quantum well is proposed, which includes the effects of a finite barrier potential, valence band anisotropy, and subband nonparabolicity.
Abstract: An analytic model is proposed for the valence-subband structure in a compressively strained quantum well which includes the effects of a finite barrier potential, valence-band anisotropy, and subband nonparabolicity. The solutions obtained for the zone-center effective mass and nonparabolicity factor are valid for both compressive and tensile strain, but the model gives a good approximation to the true band structure only in the case of compressive strain, where the nonparabolicity effects are relatively weak. For moderate compressive strain, the model provides a very fast, accurate representation of the subband structure within a few kT of the valence-band edge, which will be very useful in optoelectronic device design and simulation. The most important limitation to the model is its neglect of the strain-induced coupling to the spin-orbit split-off band, which becomes significant for large strain. Calculations performed on ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs quantum wells predict that both the effective mass and nonparabolicity decrease with increasing quantum-well width or compressive strain.
TL;DR: In this paper, the de Haas van Alphen effect of the low carrier compound CeSb has been measured by a homemade dilution refrigerator and the heavy hole orbit of β 4 in the ferromagnetic phase has been clearly observed.
Abstract: The acoustic de Haas van Alphen effect of the low carrier compound CeSb has been measured by a homemade dilution refrigerator. The heavy hole orbit of β 4 in the ferromagnetic phase has been clearly observed. The cyclotron effective mass of β 4 under the magnetic field along [001] direction was 4.3 m 0 . The angular dependence of the cross-sectional area of β 4 is well explained by the band calculation based on the p - f mixing model. Some aspects of the electron-strain interaction obtained by the oscillation intensity of the elastic constant are discussed.
TL;DR: In this article, the mechanism of leakage current through the nanoscale ultrathin silicon dioxide (SiO2) layer in a metal-insulator-semiconductor structure based on the multiple scattering theory was clarified.
Abstract: We clarify the mechanism of leakage current through the nanoscale ultrathin silicon dioxide (SiO2) layer in a metal‐insulator‐semiconductor structure based on the multiple scattering theory when technologically important phosphorus doped polycrystalline silicon is adopted as the gate electrode. We also derive an analytic expression for the direct tunneling current, and show that its measurement presents an excellent opportunity to determine the effective mass of an electron in the SiO2.
TL;DR: In this article, a reasonable fit to an analytic expression for the fluctuation-induced tunneling mechanism was obtained for the one-dimensional polypyrrole (PPy) films with dominating two-dimensional microscopic structures.
TL;DR: In this paper, the electronic structure of a 2D gas subjected to a tilted magnetic field, with a strong component parallel to the GaAs/AlGaAs interface and a weak component oriented perpendicularly, is studied theoretically.
Abstract: The electronic structure of a 2D gas subjected to a tilted magnetic field, with a strong component parallel to the GaAs/AlGaAs interface and a weak component oriented perpendicularly, is studied theoretically. It is shown that the parallel field component modifies the originally circular shape of a Fermi contour while the perpendicular component drives an electron by the Lorentz force along a Fermi line with a cyclotron frequency given by its shape. The corresponding cyclotron effective mass is calculated self-consistently for several concentrations of 2D carriers as a function of the in-plane magnetic field. The possibility of detecting its field-induced deviations from the zero-field value experimentally is discussed.
TL;DR: The overlap between two many-body wave functions for a superfluid film containing a vortex at shifted positions is calculated and the effective mass of vortices is resolved, showing it is finite.
Abstract: We calculate the overlap between two many-body wave functions for a superfluid film containing a vortex at shifted positions. Comparing the results to phenomenological theories, which treat vortices as point particles, we find that the results are consistent if the point-particle vortices are considered as under the action of the Magnus force and in weak interaction with sound waves of the superfluid. We are then able to resolve the disagreement concerning the effective mass of vortices, showing it is finite.
TL;DR: In this article, Shubnikov de Haas oscillations in the temperature range 0.3 to 2 K have been used to determine an effective mass of 0.23 m0 in a Si/Si 0.87Ge 0.13/Si two-dimensional hole gas.
Abstract: Measurements of Shubnikov de Haas oscillations in the temperature range 0.3–2 K have been used to determine an effective mass of 0.23 m0 in a Si/Si0.87Ge0.13/Si two‐dimensional hole gas. This value is in agreement with theoretical predictions and with that obtained from cyclotron resonance measurements. The ratio of the transport time to the quantum lifetime is found to be 0.8. It is concluded that the 4 K hole mobility of 11 000 cm2 V−1 s−1 at a carrier sheet density of 2.2×1011 cm−2 is limited by interface roughness and short‐range interface charge scattering.
TL;DR: In this article, the electron effective masses for Al0.15Ga0.35In0.5P and Ga 0.5In0.5P have been investigated using conventional and optically detected cyclotron resonance and the experimentally deduced values are compared with those obtained from five-band k⋅p calculation.
Abstract: The electron effective masses for Al0.15Ga0.35In0.5P and Ga0.5In0.5P have been investigated using conventional and optically detected cyclotron resonance. For AlGaInP (partly ordered) it is determined to be m*=(0.14±0.01) m0. For disordered GaInP the mass is found to be m*=(0.092±0.003) m0 and for ordered material (band gap reduction ∼50 meV) m*=(0.088±0.003) m0. The experimentally deduced values are compared with those obtained from five‐band k⋅p calculation.
TL;DR: In this article, the existence of quantum size effects in amorphous diamond-like carbon superlattice structures from optical and electronic measurements together with theoretical predictions are reported, and a ''blue shift'' in the optical gap is shown to occur with decreasing well width from which an effective mass for the electrons (and holes) is obtained.
Abstract: Evidence for the existence of quantum size effects in amorphous diamond-like carbon superlattice structures from optical and electronic measurements together with theoretical predictions are reported. A `blue shift' in the optical gap is shown to occur with decreasing well width from which an effective mass for the electrons (and holes) is obtained. Regions of negative differential resistance are observed in the current-voltage characteristics at temperatures ranging from 4–300 K. Dark conductivity studies point to a current that is dominated by a tunnelling component rather than thermal carrier emission over the barrier layers of the superlattice. Activation energy studies show an increase in the activation energy with decreasing well width, in keeping with the observed optical `blue shift'. The voltage range over which negative differential resistance is measured agrees well with resonant tunnelling predictions.
TL;DR: Angle-resolved-photoemission studies of the dispersion of the quantum-well states in copper thin films deposited on a Co(001) substrate reveal that hybridization in the interface leads to a large increase in the effective mass of the electrons.
Abstract: Angle-resolved-photoemission studies of the dispersion of the quantum-well states in copper thin films deposited on a Co(001) substrate reveal that hybridization in the interface leads to a large increase in the effective mass of the electrons. These observations have implications for theories of the oscillatory exchange coupling in the related magnetic multilayers, particularly where Fermi-surface spanning vectors away from the center of the zone are invoked as in the case of the short-period oscillation in the Co/Cu(001) multilayers.
TL;DR: An ultralow dark current normal incidence p-type strained layer In0.3Ga0.7Al/In0.52Al0.48As quantum well infrared photodetector (PSL•QWIP) was demonstrated for the first time in this paper.
Abstract: An ultralow dark current normal incidence p‐type strained‐layer In0.3Ga0.7Al/In0.52Al0.48As quantum well infrared photodetector (PSL‐QWIP) grown on (100) semi‐insulating InP substrate by molecular beam epitaxy technique for 8–12 μm infrared detection was demonstrated for the first time. This PSL‐QWIP shows background limited performance (BLIP) for T≤100 K, which is the highest BLIP temperature ever reported for a QWIP. Due to a 1.5% lattice mismatch between the substrate and quantum well, a biaxial tensile strain was created in the In0.3Ga0.7As well layers. As a result, the light‐hole state becomes the ground state for the free hole with small effective mass. The dramatic increase of optical absorption can be attributed to the large in‐plane density of states and the small light‐hole effective mass as a result of heavy‐ and light‐hole state inversion. The dark current density and BLIP detectivity for this PSL‐QWIP were found to be 7×10−8 A/cm2 and 5.9×1010 cm−√Hz/W, respectively, at λp=8.1 μm, Vb=2 V, and...
TL;DR: In this article, a self-consistent electronic property simulation of hexagonal CrSi2, MoSi2 and WSi2 is performed within the local density approximation using the semirelativistic linear muffin-tin orbital method.
Abstract: Self-consistent electronic property simulation of hexagonal CrSi2, MoSi2, and WSi2 is performed within the local density approximation using the semirelativistic linear muffin-tin orbital method. They are deduced to be narrow-gap semiconductors with indirect band gaps of 0.29,0.07, and 0.07 eV, respectively. The effective masses of holes and electrons in the disilicides are of the same order. They are close to the free electron mass in CrSi2 and there is a certain reduction of the appropriate values from chromium to tungsten disilicides. Carrier mobility calculations show that the scattering on acoustic phonons is dominant for the disilicides. The hole mobilities at 300 K are 42, 190, and 209 cm2/V s for CrSi2, MoSi2, and WSi2, respectively.
TL;DR: In this paper, the empirical pseudopotential method within the virtual crystal approximation is used to calculate the band structure of Mg1-xZnxSySe1-y, which has recently been proved to be a potential semiconductor material for optoelectronic device applications in the blue spectral region.
Abstract: The empirical pseudopotential method within the virtual crystal approximation is used to calculate the band structure of Mg1-xZnxSySe1-y, which has recently been proved to be a potential semiconductor material for optoelectronic device applications in the blue spectral region. It is shown that MgZnSSe can be a direct or an indirect semiconductor depending on the alloy composition. Electron and hole effective masses are calculated for different compositions. Polynomial approximations are obtained for both the energy gap and the effective mass as functions of alloy composition at the Gamma valley. This information will be useful for the future design of blue wavelength optoelectronic devices as well as for assessment of their properties.
TL;DR: In this paper, the authors considered the energy-gap dependence of nitrogen doping in ZnMgSSe semiconductors and estimated the ESI is located at 1.895 eV below EFS.
Abstract: Using amphoteric native defect model [Walukiewicz, Phys. Rev. B 37, 4760 (1988)], we have considered the energy‐gap Eg dependence of nitrogen doping in ZnMgSSe semiconductors. We have explained the energy‐gap Eg dependence of saturated hole concentration in ZnMgSSe semiconductors based on the amphoteric native defect model and available effective hole masses in ZnSe using the valence band discontinuity ΔEv as a fitting parameter. The Fermi‐level stabilization energy EFS and the pinned Fermi‐level energy ESI are, to a good approximation, universal for II‐VI materials as well as for III‐V materials. We have estimated the ESI is located at 1.895 eV below EFS. It is indicated that the band‐gap discontinuity between ZnSe and ZnMgSSe is ΔEc: ΔEv=0.55:0.45 if effective hole mass is 1.4 m0 for ZnMgSSe and ΔEc:ΔEv=0.67:0.33 if effective hole mass is 0.6 m0.