INFLUENCE OF PLASMON-PHONON COUPLING ON THE ELECTRON-IMPURITY INTERACTION IN THE FREE-CARRIER ABSORPTION*

An experimental and theoretical evidence that the electron-impurity scattering is modified in the presence of the electromagnetic field oscillating with the frequency corresponding to the optical phonon energy is given. The coupled plasmon-phonon mode related feature in the reflectivity spectrum can be used to determine the upper edge of the LO phonon frequency band in highly doped materials. PACS numbers: 71.45. Gm, 78.30.Fs, 72.30.+q The infrared absorption in semiconductors is mainly caused by phonons and free carriers. In many cases these mechanisms can be treated separately, each of them giving its own contribution to the optical dielectric function. The simple Drude-Zener theory assuming frequency independent damping conStants of free-carrier plasma and phonon excitations, satisfactorily describes most of the experimental reflectivity and transmission spectra in the infrared. A deviation from thiS model can be expected when the light frequency approaches the optical phonon energy band. Strong mixing of the electron plasma and polar phonon modes leading to the collective motion of electrons and lattice ions causes a significant modification of the effective scattering of electrons by impurities Most studies of the role of the dynamic screening in the free-carrier absorption were devoted to the question of plasmon excitation in the process of electron-impurity scattering (for the references see, e.g.

Electron-Electron Relaxation Effect on Auger Recombination in Direct Band Semiconductors

Influence of electron-electron relaxation processes on Auger recombination rate in direct band semiconductors is investigated. Comparison between carrier-carrier and carrier-phonon relaxation processes is provided. It is shown that relaxation processes are essential if the free path length of carriers doesn't exceed a certain critical value, which exponentially increases with temperature. For illustration of obtained results a typical InGaAsP compound is used

FREE-CARRIER PLASMONS AS A NOVEL TOOL IN SEMICONDUCTOR PHYSICS*

It is demonstrated that free-carrier plasmons, being well defined collective excitations of the electron gas in the range of small wave vectors, can serve as a sensitive tool to investigate the optical processes related to the small momentum transfers. As an example the system HgSe:Fe is analysed both experimentally and theoretically. It is well known that the excitation of the free-carrier plasma in the light absorption process is possible only in the presence of defects breaking the translational invariance of the system. Due to the overall momentum conservation requirement there must exist a momentum source to make the photon absorption *This work is supported in part by CPBP 01.06. (141

Photoemission Beyond the Sudden Approximation

The many-body theory of photoemission in solids is reviewed with emphasis on methods based on response theory. The classification of diagrams into loss and no-loss diagrams is discussed and related to Keldysh path-ordering book-keeping. Some new results on energy losses in valence-electron photoemission from free-electron-like metal surfaces are presented. A way to group diagrams is presented in which spectral intensities acquire a Golden-Rule-like form which guarantees positiveness. This way of regrouping should be useful also in other problems involving spectral intensities, such as the problem of improving the one-electron spectral function away from the quasiparticle peak.Comment: 18 pages, 11 figure

The transition from the adiabatic to the sudden limit in core level photoemission: A model study of a localized system

We consider core electron photoemission in a localized system, where there is a charge transfer excitation. The system is modelled by three electron levels, one core level and two outer levels. The model has a Coulomb interaction between these levels and the continuum states into which the core electron is emitted. The model is simple enough to allow an exact numerical solution, and with a separable potential an analytic solution. We calculate the ratio r(omega) between the weights of the satellite and the main peak as a function of the photon energy omega. The transition from the adiabatic to the sudden limit takes place for quite small photoelectron kinetic energies. For such small energies, the variation of the dipole matrix element is substantial and described by the energy scale Ed. Without the coupling to the photoelectron, the corresponding ratio r0(omega) is determined by Ed and the satellite excitation energy dE. When the interaction potential with the continuum states is introduced, a new energy scale Es=1/(2Rs^2) enters, where Rs is a length scale of the interaction potential. At threshold there is typically a (weak) constructive interference between intrinsic and extrinsic contributions, and the ratio r(omega)/r0(omega) is larger than its limiting value for large omega. The interference becomes small or weakly destructive for photoelectron energies of the order Es. For larger energies r(omega)/r0(omega) therefore typically has a weak undershoot. If this undershoot is neglected, r(omega)/r0(omega) reaches its limiting value on the energy scale Es.Comment: 18 pages, latex2e, 13 eps figure

The Kondo Resonance in Electron Spectroscopy

The Kondo resonance is the spectral manifestation of the Kondo properties of the impurity Anderson model, and also plays a central role in the dynamical mean-field theory (DMFT) for correlated electron lattice systems. This article presents an overview of electron spectroscopy studies of the resonance for the 4f electrons of cerium compounds, and for the 3d electrons of V_2O_3, including beginning efforts at using angle resolved photoemission to determine the k-dependence of the resonance. The overview includes the comparison and analysis of spectroscopy data with theoretical spectra as calculated for the impurity model and as obtained by DMFT, and the Kondo volume collapse calculation of the cerium alpha-gamma phase transition boundary, with its spectroscopic underpinnings.Comment: 32 pages, 11 figures, 151 references; paper for special issue of J. Phys. Soc. Jpn. on "Kondo Effect--40 Years after the Discovery

Symmetry of the Top Valence Band States in GaN/AlGaN Quantum Wells and its Influence on the Polarization of Emitted Light

We show theoretically that for narrow GaN/AlGaN quantum wells, lattice matched to GaN substrate/buffer and grown along the (0001) crystallographic direction the topmost valence subband symmetry depends critically on such parameters as quantum well thickness and barrier composition. This effect determines polarization of the emitted light. It is noted that the symmetry of the topmost valence band level is sensitive to the values of the $D_3$ and $D_4$ deformation potentials and can be employed in verification of existing literature values of these parameters