Long-wavelength Optical Phonons Research Articles

Raman scattering study of [hhk]-GaAs/(Si or CaF2) strained heterostructures

Raman spectroscopy is used to measure the frequency shift, symmetry, and activity of long-wavelength optical phonons in several GaAs strained epilayers. The results are compared with theoretical evaluations using the elastic compliances, phonon deformation potentials, and Raman tensors. The effect of growth direction ([001], [111], and [112]) and the substrate nature (Si or CaF2) is analyzed. The importance of nonstandard growth directions, [111] or [112], on residual stress and piezoelectric effect is discussed.

Polar-optical oscillations and electron-phonon interaction in quantum wires and quantum dots

A theory for long-wavelength optical phonons in quantum wires and quantum dots is developed under very general conditions. Confined and interface modes are obtained as solutions of the full system of four coupled second-order differential equations for the vibrational amplitudes and the electrostatic potential. These equations are solved without incompatibility between the mechanical and electrostatic matching boundary conditions. The eigensolutions and eigenmodes for cylindrical quantum wires and spherical quantum dots are found in terms of the longitudinal and transverse parts of the mechanical vibrational field and the electrostatic field, all appropriately coupled. The pure surface phonons (Fröhlich phonons) are obtained as a particular case. The orthogonality and the general conditions under which the set of eigensolutions form a complete basis are established. The electron-phonon interaction Hamiltonians are given in explicit form.

Electron-phonon interaction in GaAs/AlAs superlattices

Scattering rates of an electron in GaAs/AlAs superlattices are calculated in an envelope-function approximation which reproduces long-wavelength optical phonons almost completely. The polaron damping rate increases with decreasing layer-thickness at 300 K, while this dependence is smaller at 77 K. Intersubband relaxation rates decrease almost linearly as the layer thickness decreases. The results obtained in the dielectric continuum model agree quite well with those in the envelope-function approximation and even the bulk-phonon model explains the layer-thickness dependence reasonably well. This approximate model independence is explained by the completeness of the lattice vibration.

THE PHYSICAL PROPERTIES OF RuS2 − xSex SINGLE CRYSTALS

In this review, the preparation and characterization of the pyrite-type compound RuS 2 and RuSe 2, as well as the mixed anion compositions RuS 2 − x Se x, are systematically reported. Unusual temperature dependence in electrical transport properties characterize these compounds. Electrolyte electroreflectance measurements were used to get a better understanding of their band structure. Long-wavelength optical phonons have been studied by Raman scattering measurements at room temperature. The nature of defect in these compounds were studied by electron paramagnetic resonance (EPR) investigation. A chalcogen point defect model was established to account for the spin S = 1/2 paramagnetic species detected by EPR.

Far-infrared studies of the intermediate phases in In 2Se 3

This work reports on a study of the infrared active long-wavelength optical phonons of the layered semiconductor In 2Se 3. The temperature dependence behaviour is investigated between 10 K and 500 K, and the intermediate phases α′- and β′-In 2Se 3 are evidenced by reflectivity measurements for the E ⊥ c polarization in the spectral range 10–600 cm −1. At low temperature, the anomaly in the frequency and life-time of the LO mode is related with the α′-phase which is described as the frozen-in configuration of the longitudinal mode. During cooling down from the β-In 2Se 3 phase to the α-phase, the intermediate β′-In 2Se 3 phase is formed in the temperature range 473-363 K. The formation of the superlattice is observed and a model in which the β → α phase transition is driven by acoustic phonons is proposed.

Electron-phonon interaction in semiconductor superlattices

Scattering rates of electrons in GaAs/AlAs superlattices are calculated in an envelope-function approximation which almost completely reproduces long-wavelength optical phonons. The results are compared with those obtained in the bulk-phonon model and the dielectric continuum model, which shows that the dielectric continuum model can provide an accurate estimate of the strength of electron-phonon scattering and that even the bulk-phonon model explains the layer thickness dependence reasonably well. The underlying physics leading to this result is discussed.

The Physics of Phonons

Elements of crystal symmetry: Direct lattice Reciprocal lattice Brillouin zone Crystal structure Point groups Space groups Symmetry of the Brillouin zone Jones zone Surface Brillouin zone Matrix representations of point groups. Lattice dynamics in harmonic approximation - semiclassical treatment: Introduction Lattice dynamics of a linear chain Lattice dynamics of three-dimensional crystals - phenomenological models Density of normal modes Numerical calculation of g(w) Lattice heat capacity. Lattice dynamics in the harmonic approximation - ab initio treatment: Introduction The frozen-phonon approach The linear response approach The planar force constant method. Anharmonicity: Introduction Hamiltonian of a general three-dimensional crystal Effect of anharmonicity on phonon states Effects of the selection rules on three-phonon processes Hamiltonian of an anharmonic elastic continuum Evaluation of three-phonon scattering strengths The quasi-harmonic approximation and Grueneisen's constant. Theory of lattice thermal conductivity: Introduction Relaxation-time methods Gree-Kubo linear response theory Second sound and Poiseuille flow of phonons. Phonon scattering in solids: Boundary scattering Scattering by static imperfections Phonon scattering in alloys Anharmonic scattering Phonon-electron scattering in doped semiconductors Phonon scattering due to magnetic impurities in semiconductors Phonon scattering from tunnelling states of impurities Phonon-photon interaction. Analysis of phonon relaxation and thermal conductivity results: Anharmonic decay of phonons Lattice thermal conductivity of undoped semiconductors and insulators Non-metallic crystals with high thermal conductivity Thermal conductivity of complex crystals Low-temperature thermal conductivity of doped semiconductors. Phonons in low dimensional solids: Introduction Surface vibrational modes Attenuation of surface phonons Phonons in superlattices Thermal conductivity of superlattices. Phonons in impure and mixed crystals: Introduction Localised vibrational modes in semiconductors Experimental studies of long-wavelength optical phonons in mixed crystals Theoretical models for long-wavelength optical phonons in mixed crystals Phonon conductivity of mixed crystals. Phonons in quasi-crystalline and amorphous solids: Introduction Phonons in quasi-crystals Structure and vibrational excitations of amorphous solids Vibrational properties of amorphous solids Low-temperature properties of amorphous solids. Phonon spectroscopy: Introduction Heat pulse technique Superconducting tunnel junction technique Optical techniques Phonons from Landau levels in 2DEG Phonon focusing and imaging Frequency crossing phonon spectroscopy Phonon echoes. Phonons in liquid helium: Introduction Dispersion curve and elementary excitations Specific heat Interactions between the excitations Kapitza resistance Quantum evaporation. Appendices: Density functional formalism The pseudopotential method Evaluation of integrals in sections 6.4.1.4 Negative-definitenss of the phonon off-diagonal operator ^D*L. References. Index.

Optical phonons in GaAs/AlAs quantum wires.

Phonon-dispersion curves of semiconductor quantum wires are studied in a realistic rigid-ion model. We introduce an approach for solving the rigid-ion model in quantum wires, which avoids direct computation of the Coulomb interaction. Our calculations demonstrate the interesting anisotropic behavior of long-wavelength optical phonons in quantum wires. In particular, we show that frequencies of several optical phonons approach different values as the wave vector approaches the zone center from three different axes. We have also shown that the lateral confinement in a quantum wire on the interface modes leads to the edge modes.

Electron-phonon interaction, dynamical screening and collective excitations in heterostructures: III. Coupled intra- and intersubband plasmon-phonons

The complete spectrum of elementary excitations for the quasi two-dimensional electron gas interacting with the optical phonons of semiconductor heterostructures is calculated within the random-phase approximation. The dispersion curves of the coupled intra- and intersubband plasmon-phonons are plotted in graphical form for various cases. Considering the intersubband mixing we found that this yields only a very weak contribution to the dispersion curves of the plasmon-phonon modes. The theoretical results for the dispersion curve of the (0-0) intrasubband plasmons obtained, including exchange and correlation effects, coupling to the long-wavelength optical phonons, intersubband mixing and screening effects of the grating on top of the sample agree very well with experimental results from far-infrared transmission spectroscopy.

Temperature dependence of long-wavelength optical phonons in AlSb

We have studied the temperature dependence of the transverse and longitudinal long wavelength optical phonons of AlSb. The direct and indirect anharmonic contributions to the frequency shift and broadening are determined as a function of temperature. They are associated with phonon anharmonic decays and volume contribution, respectively.

Correction of longitudinal long-wavelength optical phonon frequency in KC1

Abstract The longitudinal optical phonon frequency ωLO in KC1 was determined from the infrared reflectivity spectra with the factorized form of dielectric function. Obtained value is about 10% smaller than the data reported already. The origin of this discrepancy is attributed to be an error arised in an inadequate analysis since the analysis does not treat separately the reststrahlen band and its shoulder. The determined ωLO exhibits a reasonable relation to the dielectric parameters and also the reasonable temperature dependence. These results may support above attribution and also suggest the correction of ωLO for many other ionic compounds.

Long-wavelength optical phonons in Ag3B5IIIC9VI single crystals

Crystal Research and TechnologyVolume 25, Issue 3 p. K53-K57 Short Note Long-wavelength optical phonons in Ag3B5IIIC9VI single crystals Prof. N. M. Gasanly, Prof. N. M. Gasanly Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorA. G. Guseinov, A. G. Guseinov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorV. I. Tagirov, V. I. Tagirov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorE. A. Aslanov, E. A. Aslanov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorS. A. El-Hamid, S. A. El-Hamid Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this author Prof. N. M. Gasanly, Prof. N. M. Gasanly Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorA. G. Guseinov, A. G. Guseinov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorV. I. Tagirov, V. I. Tagirov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorE. A. Aslanov, E. A. Aslanov Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this authorS. A. El-Hamid, S. A. El-Hamid Physics Department, Azerbaijan State University, P. Lumumba Str. 23, Baku, 370602, USSRSearch for more papers by this author First published: March 1990 https://doi.org/10.1002/crat.2170250323Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume25, Issue3March 1990Pages K53-K57 RelatedInformation

Phonon surface loss function of ionic-crystal films: A comparison between microscopic and macroscopic approaches

The surface loss function is an important quantity in the description of reflection electron-energy-loss spectroscopy (EELS) in near-specular geometry. In this paper, lattice-dynamics calculations of the surface energy-loss function associated with optical excitations in ionic-crystal slabs are performed. Test calculations are carried out for both NaF isolated films and NaF slabs onto a semi-infinite substrate. In the latter case, a continuum dielectric theory is used to describe the response of the substrate, emphasis being on long-wavelength optical phonons. We compare the results of the microscopic formulation of the surface loss function of the film with those deduced from the so-called dielectric theory, where a bulk-like dielectric response of the slab is assumed. The legitimacy of the use of a bulk response is a central question in applications of the dielectric theory to a very thin slab. It is shown that the latter provides a valid description of the surface energy-loss function for the wave vectors predominantly probed in EELS when the film thickness exceeds ~ 2 nm (about 10 atomic planes). For very thin, relaxed films (less than 8 atomic layers), the dielectric theory fails in producing the correct frequency positions of the surface energy-loss peaks; by contrast the intensities of the loss peaks are more accurately predicted.

A model for longitudinal optical phonons and electron-phonon coupling in GaAs/GaAlAs multilayer structure

A new model for long-wavelength longitudinal optical phonons in GaAsGaAlAs multi-layer structures is presented. Depending on the layer, the relative ionic displacements are written on the basis of GaAs or GaAs-type longitudinal optical phonons and treated in the framework of the Born-Huang model generalized to include isotropic dispersion effects in the Brillouin zone centre. For double heterostructures, a finite number of quantized confined modes is found. Interplay between the long range Coulomb interaction, which couples the vibrations of adjacent GaAs layers, and confinement effects, which prevent the displacements of adjacent GaAs layers to overlap, is evidenced in the case of superlattices. The strength of the electron-phonon coupling in double heterostructures stays within a factor of 2 of the electron-bulk phonon effective coupling strength for practical values of the parameters.

Long-wavelength lattice dynamics of GaxIn1−xAsySb1−y quaternary alloys

The quaternary semiconductor alloy GaxIn1−xAsySb1−y has been investigated using Raman scattering spectroscopy in the spectral region from 150 to 300 cm−1 at room temperature. The Raman spectra exhibit two- or three-mode behavior depending on the composition. A modified random-element isodisplacement model is used to describe the behavior of the optical phonons. The calculations of the dependence of the long-wavelength optical phonon frequencies on the composition are in good agreement with the experimental results.

Lattice vibration spectra of GaP1−xSbx and InP1−xSbx

Raman scattering spectra of ternary semiconductor alloys GaP1−xSbx and InP1−xSbx have been investigated in the spectral region from 150 to 450 cm−1 at room temperature. The optical phonons of both GaP1−xSbx and InP1−xSbx exhibit ‘‘two-mode’’ behavior over the whole composition range. A random element isodisplacement model is used to describe the behavior of the optical phonons of both alloy systems. The calculations of the dependence of the long-wavelength optical phonon frequencies on the composition are in good agreement with the experimental results.

Raman and infrared phonon piezospectroscopy in InP.

We have studied the effect of a uniaxial stress on the long-wavelength optical phonons of InP using Raman and far-infrared spectroscopic techniques. The Raman measurements were performed with laser lines in regions of both transparency and opacity, using infrared and visible lasers, respectively. Phonon and effective-charge deformation potentials have been obtained from the data, and also an estimate of the Faust-Henry coefficient from the integrated scattering intensities. Comparison of the Raman and infrared reflectivity results allows us to conclude that the applied stress is relaxed toward the surface of the sample.

Electron-optical-phonon interaction in semiconductor multiple-quantum-well structures.

The $1s\ensuremath{-}2p(m=+1)$ hydrogenic transition in magnetic fields up to 20 T for shallow donor impurities confined in 138-\AA{} GaAs wells in AlGaAs/GaAs multiple-quantum-well structures has been used to investigate the electron-optical-phonon interaction. A resonant "pinning" behavior has been observed at energies well below (\ensuremath{\sim}50 ${\mathrm{cm}}^{\ensuremath{-}1}$) that of the long-wavelength optical phonons of GaAs. It is suggested that these surprising results may be explained by interaction with near-zone-boundary longitudinal-optical phonons activated by the superlattice.

Lattice dynamics of thallium iodide

The long-wavelength optical phonons in orthorhombic TlI are calculated employing a shell model and transferring the potential parameters from cubic TlI and TlBr. Satisfactory agreement between experimental Raman and infrared phonons suggests that the change in the crystal structure alone is the main reason for the redistribution of phonons in the cubic to orthorhombic transition.

Long-wavelength optical phonons in polar superlattices.

A simple microscopic theory is developed to study the optical phonons in polar semiconductor superlattices near the zone center. This theory is based on a rigid-ion model with a simplified Coulomb interaction. With this theory one can gain much understanding about the anisotropic behavior of long-wavelength optical phonons and the interface modes in polar superlattices.