Electron-phonon scattering in an asymmetric double barrier resonant tunneling structure

We calculate the electron-phonon scattering rate for an asymmetric double barrier resonant tunneling structure based on dielectric continuum theory, including all phonon modes, and show that interface phonons contribute much more to the scattering rate than do bulk-like LO phonons for incident energies which are approximately within an order of magnitude of the Fermi energy. The maximum scattering rate occurs for incident electron energies near the quantum well resonance. Subband nonparabolicity has a significant influence on electron-phonon scattering in these structures. We show that the relaxation time is comparable to the dwell time of electrons in the quantum well for a typical resonant tunneling structure. Received: 23 December 1997 / Revised: 24 March 1998 / Accepted: 9 March 1998     

Q-dependent light scattering by electrons in LaB6

The inelastic light scattering by intraband electronic excitations in metallic lanthanum hexaboride has been studied in the temperature range of 10–300 K. General agreement has been obtained between the measured spectra and the spectra calculated within the band theory taking into account the renormalization of electron energies owing to electron-phonon scattering. The electron-phonon coupling constant λ and electron relaxation frequency Γ have been estimated. The dependence of the electron self-energies on the direction and magnitude of the wave vector has been revealed, implying the anisotropic electron-phonon interaction or the contribution from other electron scattering mechanisms.     

Effect of normal phonon-phonon scattering on the mutual electron-phonon drag and kinetic phenomena in degenerate conductors

The effect of normal phonon-phonon scattering processes on momentum relaxation in a nonequilibrium electron-phonon system is considered. A system of rate equations for the electron and phonon distribution functions has been solved with the inclusion of mutual electron-phonon drag. The kinetic coefficients of conductors have been calculated in a linear approximation in the degeneracy parameter. The effect of normal phonon-phonon scattering processes on the electron-phonon drag and on the kinetic phenomena in conductors with degenerate carrier statistics is analyzed.     

Inelastic light scattering in the Eu and Yb monochalcogenides

Multiphonon inelastic light scattering has been investigated in the magnetically ordering Eu and in the diamagnetic Yb monochalocogenides. All aspects of this scattering suggest that the multi-phonon lines results from recombination during time resolved relaxation ot the excited “hot” electron. The multiphonon scattering in these compounds is therefore interpreted by a two-step process of absorption followed by emission (hot luminescence). The observation of zone-center and zone-boundary multiphonon scattering is related to the electron-phonon coupling which is dependent on the kinetic energy of the excited photo-electron. Hence, with excitation into the bottom of the conduction band the coupling to the phonon system is dominated by the Fröhlich polaron concept, leading to zone-center LO scattering, whereas at higher excitation energies the electron-phonon coupling is no longer selective and is dependent primarily on the LO phonon density of states. The relaxation process and the electron-phonon coupling are strongly dependent on magnetic order. However, by comparison of the Eu monochalcogenides with the corresponding Yb compounds it is evident that the general phenomenon of multiphonon scattering in these compounds is independent of a spin system and is determined alone by the unique band structure.     

Modifying electron-phonon scattering rates in semiconductor quantum wells with thin AlAs layers

We have studied theoretically the electron-phonon scattering rates in GaAs/AlAs quantum wells which have additional thin AlAs layers in them using the dielectric continuum approach for the phonons. The confined and interface phonon modes and the intersubband electron phonon scattering rates of these structures have been calculated. The system with an additional AlAs layer is found to have intersubband electron scattering rates which are increased modestly as compared to those for the corresponding quantum well. These results show that scattering rates in general are expected to depend only weakly on the effects of system structure on the optical phonon spectra.     

Post-transient relaxation in graphene after an intense laser pulse

High intensity laser pulses were recently shown to induce a population inverted transient state in graphene [T. Li, et al., Phys. Rev. Lett. 108, 167401 (2012)]. Using a combination of hydrodynamic arguments and a kinetic theory we determine the post-transient state relaxation of hot, dense, population inverted electrons towards equilibrium. The cooling rate and charge-imbalance relaxation rate are determined from the Boltzmann-equation including electron-phonon scattering. We show that the relaxation of the population inversion, driven by inter-band scattering processes, is much slower that the relaxation of the electron temperature, which is determined by intra-band scattering processes. This insight may be of relevance for the application of graphene as an optical gain medium.     

Rate of Decoherence for an Electron Weakly Coupled to a Phonon Gas

We study the dynamics of an electron weakly coupled to a phonon gas. The initial state of the electron is the superposition of two spatially localized distant bumps moving towards each other, and the phonons are in a thermal state. We investigate the dynamics of the system in the kinetic regime and show that the time evolution makes the non-diagonal terms of the density matrix of the electron decay, destroying the interference between the two bumps. We show that such a damping effect is exponential in time, and the related decay rate is proportional to the total scattering cross section of the electron-phonon interaction.     

Current relaxation processes in highly excited semiconductors

We compare the conductivity relaxation time due to electron-hole scattering to the one due to electron-phonon scattering. We first calculate the variations of both scatterings with the electron-hole plasma density from the dilute to the metal-like regime, using the appropriate screenings of the interaction potentials; we find that, unexpectedly, the electron-hole collisions dominate the electron-phonon scattering, not at very large density, but instead, at intermediate density, when the plasma becomes degenerate.     

Wannier-Stark effect and electron-phonon interaction in macroporous silicon structures with SiO2 nanocoatings

We investigated the contribution of electron-phonon interaction to the broadening parameter Γ of the Wannier-Stark ladder levels in oxidized macroporous silicon structures with different concentration of Si-O-Si states (TO and LO phonons). The obtained value of the Wannier-Stark ladder parameter Γ is much less than the djacent level energy evaluated from giant oscillations of resonance electron scattering on the surface states. We determined the influence of broadening on the oscillation amplitude in IR absorption spectra as interaction of the surface multi-phonon polaritons with scattered electrons. This interaction transforms the resonance electron scattering in samples with low concentration of Si-O-Si states into ordinary scattering on ionized impurities for samples with high concentration of Si-O-Si states. The transformation takes place at the scattering lifetime coinciding with the period of electron oscillations in the surface electric field.     

Elastic and inelastic scattering of electrons by vibrating impurities in semiconductors

Elastic and inelastic scattering of conduction electrons by vibrating ionized impurities in valence semiconductors is investigated. For elastic scattering, the modification of the Brooks-Herring formula arising from impurity vibrations is unimportant for all conceivable electron temperatures and donor concentrations. Similarily, for inelastic (one-phonon) processes, the change in electron-phonon relaxation time (or in electron-lattice coupling constant) arising from vibrations of the ionized centres is entirely negligible.     

锐钛矿和金红石二氧化钛中光生载流子的超快动力学：电声相互作用研究

本文结合玻尔兹曼输运方程和电声散射速率计算研究锐钛矿和金红石二氧化钛中光生载流子的超快动力学过程. 其中,动力学模拟所需的结构参数均通过第一性原理计算获得. 结果表明,由于存在强Fr?hlich型电声耦合,纵光学声子模对两个晶相的能量弛豫过程均有十分显著的影响,但是两个晶相的弛豫机理却表现出明显的差异. 对于单条导带内的弛豫过程,锐钛矿和金红石的能量弛豫时间分别为24.0 fs和11.8 fs,前者约为后者的二倍. 这一差异来源于两个晶相中不同的电子扩散分布以及不同的声学模散射贡献. 对于涉及多条导带的弛豫过程,预测的锐钛矿和金红石的总体弛豫时间分别为47 fs和57 fs,其相对大小与单条导带的情况相反. 分析表明金红石相弛豫较慢是因为存在多个速率控制步骤. 这些发现为调控电子动力学以及设计高效的二氧化钛器件提供了有价值的信息.     

Deviation from matthiessen's rule of dilute Al-alloys computed by 4-OPW approximation

Deviation from Matthiessen's rule (DMR) for five Al based alloys (AlAg, AlMg, AlZn, AlGa and AlGe) are calculated at 20, 50, and at 100 K by 4-OPW approximation. The published data of electron-phonon relaxation time and those of electron-impurity relaxation time are used. The Caplin-Rizzuto plots of calculated DMR agree with experimental data at lower temperature. At higher temperature it is suggested that interference effect of the two scattering agents must be taken into account to get better agreement.     

On different mechanisms of electron-phonon scattering of electron and hole excitations on an Ag(110) surface

We present the results of a detailed theoretical study of the electron-phonon scattering of electron and hole excitations in the unoccupied and occupied surface states on an Ag(110) surface. We show that the electron-phonon coupling parameter λ in the unoccupied surface state is approximately three times smaller than that in the occupied one, because the scattering of these states is determined by different phonon modes. The difference in the phonon-induced decay mechanisms of electron and hole excitations is determined by different spatial localizations of the unoccupied and occupied surface states at the $ \overline Y $ \overline Y point of the two-dimensional Brillouin zone.     

Electron-phonon interaction inP-doped silicon at low temperatures

In this present work, we explain the thermal conductivity results ofP doped silicon for impurity concentration 4.7×10¹⁷ and 1.0×10¹⁸ cm^–3 by applying the theory of scattering of phonons by electrons in the mixed state i.e. both in the localised state and in the metallic state. Using Mikoshiba's inhomogeneity model we calculated the number of electrons in the bound region and in the conduction band region and using the relaxation rates of both bound electron-phonon scattering and Ziman-Kosarev theory of free electron-phonon scattering, we explain the thermal conductivity values from 2 to 40 K. The values of density-of-states effective mass and dilatation deformation potential are found to be in agreement with the experimental values for silicon, for the electron concentration in the conduction band. We have also taken into account the effect of impurity scattering due to doped impurities, along with isotope scattering.     

Non-Fermi-liquid behavior of compressible electron states on the lowest Landau level

Experiments show that at even denominator fractions (EDF) (7p = 1=2;3=4;3=2,...) the two-dimensional electron gas (2DEG) in a strong magnetic field becomes compressible, has no energy gap, and demonstrates the presence of an ostensible Fermi surface (FS). Since this phenomenon results from a minimization of the interaction, rather than the kinetic energy, the EDF states might well exhibit deviations from a conventional Fermi liquid (FL). We show that impurity scattering and its interference with electronelectron and electron-phonon interactions provide examples of intrinsically non-Fermi-liquid (NFL) transport at EDFs.     

Generalized Elliott-Yafet theory of electron spin relaxation in metals: origin of the anomalous electron spin lifetime in MgB2

The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.     

Deviation from Matthiessen rule in Mg-Cd and Cd-Mg

The interference term between electron-phonon and electron impurity scattering has been evaluated for $\text{Mg}$Cd and $\text{Cd}$Mg and found to be negative, in agreement with experiment. It is shown that measurements on single crystal should give valuable information.     

The frequency dependence of phonon interactions at Terahertz-frequencies studied by time-resolved phonon spectroscopy

Phonon properties concerning propagation, frequency spectrum and lifetime in the Terahertz range have been investigated. The phonons have been produced by square wave Joule heating of thin constantan films evaporated onto a strongly doped ruby. Cross sections for phonon scattering at the Cr³⁺ impurity ions of the ruby were determined as a function of frequency. The theoretical estimate for mass defect scattering given by Klemens [9] is found to agree reasonably with the experimental results. Lifetime measurements indicate that phonons in ruby preferentially propagate in the transversal mode. Phonon frequency spectra in the constantan films were measured under experimental conditions, where the strength of electron phonon coupling is significant; thus electron-phonon relaxation times could be obtained as a function of frequency.     

Electron-phonon interaction effect on optical absorption in cylindrical quantum wires

Electron-phonon interaction effects on linear and nonlinear optical absorption in cylindrical quantum wires are investigated. The linear and nonlinear optical absorption coefficients are obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for GaAs/AlAs cylindrical quantum-well wires. The results show that electron-phonon interaction not only influences the relaxation rate but also distinctly influences the wave functions and energies of the electron. The correction of electron-phonon interaction effect on the wave functions of the electron dominates the values of absorption coefficients. Moreover, the correction of electron-phonon interaction effect on the energies of the electron makes the absorption peaks blue shift and become wider.     

The kinetics of low-temperature electron-phonon relaxation in a metallic film following instantaneous heating of the electrons

The theoretical analysis of experiments on pulsed laser irradiation of metallic films sputtered on insulating supports is usually based on semiphenomenological dynamical equations for the electron and phonon temperatures, an approach that ignores the nonuniformity and the nonthermal nature of the phonon distribution function. In this paper we discuss a microscopic model that describes the dynamics of the electron-phonon system in terms of kinetic equations for the electron and phonon distribution functions. Such a model provides a microscopic picture of the nonlinear energy relaxation of the electron-phonon system of a rapidly heated film. We find that in a relatively thick film the energy relaxation of electrons consists of three stages: the emission of nonequilibrium phonons by “hot” electrons, the thermalization of electrons and phonons due to phonon reabsorption, and finally the cooling of the thermalized electron-phonon system as a result of phonon exchange between film and substrate. In thin films, where there is no reabsorption of nonequilibrium phonons, the energy relaxation consists of only one stage, the first. The relaxation dynamics of an experimentally observable quantity, the phonon contribution to the electrical conductivity of the cooling film, is directly related to the dynamics of the electron temperature, which makes it possible to use the data of experiments on the relaxation of voltage across films to establish the electron-phonon and phonon-electron collision times and the average time of phonon escape from film to substrate. Zh. éksp. Teor. Fiz. 111, 2106–2133 (June 1997)