The diagrammatic expansion of absorption-edge singularities for a nonequilibrium Fermi sea is performed, up to second order in the conduction-electron–deep-hole final-state interaction. To this end, we use a nonstandard electron Green’s function that we have adequately modified to take the nonequilibrium Fermi sea into account. This second-order diagrammatic expansion allows us to validate this Green’s function, which we will use in a nonperturbative solution of the problem. This approach also puts the absorption in a different light, when compared to the physical picture provided by simple second-order perturbation theory (paper I). Finally, it allows us to determine securely the part of the critical exponent associated with excitations of electron-hole pairs in the Fermi sea.

Light-induced specular rotation resulting from a time-nonreversible nonreciprocal interaction of light with semiconductors of zinc-blende structure is reported. The rotation increases with pump intensity at the rate of 1.1×${10}^{\mathrm{-}11}$ rad ${\mathrm{W}}^{\mathrm{-}1}$ ${\mathrm{cm}}^2$ in GaAs and 4.3×${10}^{\mathrm{-}11}$ rad ${\mathrm{W}}^{\mathrm{-}1}$ ${\mathrm{cm}}^2$ in InSb and does not disappear immediately after the end of the excitation, but partially decays on a subnanosecond time scale.

We calculated ${\mathrm{\varepsilon }}_{\mathrm{\infty }}$ and second-order nonlinear coefficients d=${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$/2 for four SiC polytypes as well as ${\mathrm{\varepsilon }}_{\mathrm{\infty }}$ for diamond within the local-density approximation (LDA), and using the LDA wave functions with a self-energy correction in the form of a scissors operator Δ${\mathit{P}}_{\mathit{c}\mathbf{k}}$ to adjust the band gaps. For all the wide-band-gap materials we have studied so far, we find that the Δ needed to reproduce the optical response properties is less than the Δ deduced by GW calculations or needed to reproduce the experimentally observed band gaps. This is in contrast to the small- to medium-gap semiconductors we studied previously. For nH SiC with n≥4, our predictions for d are close to the only experimental data. Our calculations show that both d and the local-field corrections to d for nH SiC form a trend as n→∞. The ${\mathit{d}}_{113}$/${\mathit{d}}_{333}$ ratios we predicted for different SiC polytypes differ from those of bond-charge-model predictions.

We show that an exciton is self-trapped at the well-known ABC optical center in silicon by a lattice relaxation of 35±3 meV. The self-trapping arises from the electron component of the exciton, which is highly localized within about one atomic spacing of the core of the optical center. The effects of compressive stresses on the photon energy and polarization of the ABC luminescence band are reported for temperatures of 4.2 and 20 K. They can be fitted accurately by expressing the bound exciton states as perturbed band states of the silicon. The deformation potentials required for the hole component of the exciton are very close to those of the perfect lattice, consistent with the hole being only weakly localized on the center, while the deformation potential of the electron is modified by its strong localization. The center is thus a particularly clear case of a ‘‘pseudoacceptor’’ isoelectronic center, with properties that appear to be highly localized or weakly localized depending on the particular measurement. The importance of the lattice relaxation in binding the exciton implies that symmetry determinations by optical measurements may not measure the symmetry of the unrelaxed core of the defect.

Czochralski-grown Si samples were irradiated by fast neutrons, at room temperature, with the aim of studying the identity of the defects produced, using infrared spectroscopy. Two localized vibrational modes at 914 and 1000 ${\mathrm{cm}}^{\mathrm{-}1}$ were considered as intermediate defect stages between VO and ${\mathrm{VO}}_2$ complexes. We express the view that they may arise from a [VO+${\mathrm{O}}_{\mathit{i}}$] defect where an interstitial oxygen atom is trapped near a VO pair. Another two peaks at 1032 and 1043 ${\mathrm{cm}}^{\mathrm{-}1}$ were attributed to the ${\mathrm{VO}}_4$ defect and a tentative model of its structure is presented.

We present a study of the structure of a-${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{C}}_{\mathit{x}}$:H alloys by wide-angle x-ray scattering. By carefully analyzing the radial distribution functions and comparing with previous extended x-ray-absorption fine-structure measurements, we provide a detailed and quantitative description of local bonding around Si and C atoms. Among the results presented, most noteworthy are constant interatomic distances in first and second shells and the detection of a strong tendency for chemical order.

The defect theory of Hjalmarson et al. [Phys. Rev. Lett. 44, 810 (1980)] combined with the bond-orbital model of Baranowski [J. Phys. C 17, 6287 (1984)] are used to calculate the wave function and hyperfine-interaction tensor of the ${\mathrm{Sb}}_{\mathrm{Ga}}$ heteroantisite defect in GaAs. The defect potential is extended to the nearest-neighbor sites. The hyperfine-interaction constants are in good agreement with the electron paramagnetic resonance data. The results show that the outward relaxation of nearest-neighbor atoms must be taken into account for the quantitative description of this defect.

We present Raman spectra of InP measured under nonresonant conditions revealing multiphonon processes up to fifth order. Using an incident photon energy in the absorption region of the compound but far from any of its interband transitions, nonresonant multiphonon processes of order higher than two, which have not been reported so far in a zinc-blende-type semiconductor, have been observed in indium phosphide. In this way it has been possible to detect contributions not only from the longitudinal optical phonons but also from the transverse optical phonons in the higher-order peaks. We find a very good agreement between multiples of the TO- and LO-phonon frequencies at the zone center and the higher-order phonons measured in the experiments. The trend of strong intensity reductions observed when passing from first to second as well as from second to third order is not maintained when going from third to fourth, and from fourth to fifth order.

We applied a simplified microscopic two-site double-well model of small bipolarons (SB’s) executing thermally enhanced adiabatic tunneling to calculate the complex dynamic conductivity of chalcogenide glasses in good quantitative agreement with the experimental data for ${\mathrm{As}}_2$${\mathrm{Se}}_3$. It was found that in these materials (i) the primary mechanism for the ac conductivity is SB hopping, which at low temperatures involves adiabatic tunneling in the atomic subsystem; (ii) the intersite distance (not the energy disparity) is the principal source of the relaxation time dispersion; (iii) the stretched bonds of the size of 4.0±0.6 Å with the concentration of the order of ${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ are responsible for observed dielectric losses in a wide range of temperatures (0–600 K) and frequencies (${10}^2$–${10}^8$ Hz); (iv) the spatial distribution of the SB sites as well as of their occupation numbers are strongly affected by the pair Coulombic correlations. Both the temperature and the frequency dependencies of the real part of the ac conductivity as well as of the dielectric losses’ tangent have been discussed.

We have focused our attention on the valence-band density of states (VB-DOS) of near-noble-metal monosilicides (NiSi, PdSi, and PtSi) from the study of soft-x-ray-emission spectroscopy. These three silicides have several similarities, i.e., electron configuration for each metal atom and crystallographic structure of each silicide. However, the spectral shape of the Si ${\mathit{L}}_{2,3}$ emission, which has information of the Si s and/or the d VB-DOS, of each silicide has indicated the clear differences from each other. Moreover, it is shown that these characteristics are closely related to the features observed in the Si p state derived from Si Kβ emission spectra. From the spectral analysis related to the energy difference between Si p bonding and antibonding states considering the interaction strength of the Si p-metal d of each silicide, the influence of Si-Si interatomic distance on the value of the full width at half maximum of the Si s bonding state and the Si s and/or d contribution on the upper part of the VB-DOS structure, we have suggested a valence-band structure of near-noble-metal monosilicides.

The quantum magnetotransport properties of a nondegenerate two-dimensional gas of electrons interacting with helium-vapor atoms above a liquid-helium surface is studied in magnetic fields up to 20 T by the ac capacitive coupling technique. The data and the theoretical analysis performed show that in the ultraquantum limit the generalized or effective collision frequency ${\nu }_{\mathrm{eff}}$ of the electrons increases faster with magnetic field than the cyclotron frequency ${\mathrm{\omega }}_{\mathit{c}}$. Under extremely strong magnetic fields, where the Landau level width becomes comparable to or larger than the thermal energy, the high-cyclotron-frequency approximation ${\mathrm{\omega }}_{\mathit{c}}$≫${\nu }_{\mathrm{eff}}$, usually assumed in quantum transport theories, is no longer valid. The self-consistent Born-approximation theory is extended to be valid for any ratio of ${\mathrm{\omega }}_{\mathit{c}}$ to ${\nu }_{\mathrm{eff}}$. Then it describes the data perfectly without any adjustable parameter. The results reported here also give strong support to the universality of the linear Hall resistivity.

A minimal-parameter tight-binding theory incorporating explicit use of nonorthogonality of the basis, is used to generate a transferable scheme for silicon. Good results are obtained for band structure, phase diagram, and bulk phonons. The diamond structure is found to be the ground state even when compared with the clathrate structure. The results for clusters show good agreement with ab initio predictions. The theory differs from the conventional orthogonal schemes in three main respects: (1) only three adjustable parameters are employed, (2) no artificial cutoff is used for interactions and, (3) the need for a coordination-dependent energy term has been obviated for clusters of any size.

Several recent experiments have measured the rates of momentum relaxation and energy relaxation due to carrier-carrier scattering in GaAs as a function of density in three dimensions and in two dimensions. This paper examines the power laws for the density and temperature dependence of these rates based on the Boltzmann equation for electron-electron scattering, from both analytical arguments and numerical calculations. The experimental scaling with density is deduced for three-dimensional scattering over four orders of magnitude of density variation and two-dimensional scattering over two orders of magnitude. The effects of frequency-dependent terms in the random-phase approximation for the dielectric function are taken into account, as well as the effects of electron-hole scattering.

We investigate in detail the creation of mestastable dangling bond defects in undoped hydrogenated amorphous silicon by illumination with pulsed-light sources. Based on the electron-hole recombination model for defect creation, the kinetics of the defect generation process is analyzed theoretically for different experimental conditions (pulse length, pulse energy, repetition rate, and average intensity). These theoretical results are then compared to experimental observations using both monochromatic and polychromatic (‘‘white light’’) pulse sources. Implications of pulse illumination for accelerated testing of the stability of amorphous-silicon-based solar cells are also discussed.

We calculate the line shapes and total oscillator strengths for phonon-assisted recombination from polyexcitons, complexes involving two, three, or four excitons, in Si. Line shapes are determined from ground-state to ground-state transition matrix elements, using variationally determined correlated wave functions. Transition matrix elements are calculated with Monte Carlo methods. We find that about 90% of the total oscillator strength in the decay of the larger complexes can be accounted for by the ground-state to ground-state mechanism, obviating the need for consideration of excited final states. The line shapes and widths of the larger complexes are similar to that of the biexciton, with oscillator strength per exciton increasing slightly with increasing complex size due to many-body effects.

Temperature and many-body effects on the intersubband transition in a GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As multiple quantum well are studied using the infrared-absorption technique and the envelope-function-approximation method. In order to explain the measured peak position energy of the intersubband transition and its blueshift observed by decreasing temperature and/or increasing the two-dimensional electron-gas density, a theoretical model is developed which is based on a nonparabolic-anisotropic envelope-function-approximation (NAEFA) method. This model takes into account the many-body corrections, in particular, temperature-dependent electron-electron intrasubband and intersubband exchange and direct Coulomb interaction energies as well as the depolarization and excitonlike shifts within the framework of Zaluzny’s implementation of Ando’s formalism [Phys. Rev. B 43, 4511 (1991)]. Temperature-dependent effective masses, nonparabolicity, conduction-band offsets, the Fermi level, and line-shape broadening are also incorporated in the present NAEFA calculations. Our theory provides a qualitative explanation for the magnitude of the measured temperature blueshift. Additional support for many-body effects is obtained by utilizing the persistent photoeffect measurements.

We have investigated the exciton spin dynamics in quantum wells. In nonresonant excitation conditions, the initial degree of circular polarization of the exciton luminescence is higher than the excitation light polarization. This demonstrates that excitons are formed from nongeminate electron-hole pairs. The understanding of the exciton formation process allows us to propose a method to measure directly the hole spin-relaxation time (${\mathrm{\tau }}_{\mathit{h}}$) in intrinsic quantum wells. We show how the analysis of the total photoluminescence intensity under circularly and linearly polarized excitation allows us to measure ${\mathrm{\tau }}_{\mathit{h}}$, independently of the other spin-flip processes.

We have studied the quantum transmission properties of serial stub and loop structures. Throughout we have considered free-electron networks and the scattering arises solely due to the geometric nature of the problem. The band formation in these geometric structures is analyzed and compared with the conventional periodic-potential scatterers. Some essential differences are pointed out. We show that a single defect in an otherwise periodic structure modifies band properties nontrivially. By a proper choice of a single defect one can produce positive-energy bound states in continuum, in the sense of von Neumann and Wigner. We also discuss some magnetic properties of loop structures in the presence of Aharonov-Bohm flux.

The deliberate use of surfactants during the growth of Ge on Si(001) prevents the formation of three-dimensional clusters and allows the deposition of continuous and smooth Ge films. This, however, is not valid for the regime of strained film growth prior to the generation of misfit-relieving defects. Using Sb as the surfactant, an 8-ML-thick pseudomorphic Ge film exhibits a pronounced microroughness on an angstrom scale. The average terrace width is only ∼10 Å. Up to 4–5 vertical layers are simultaneously visible at the surface. This microroughness allows the Ge atoms (which are under compressive stress) to relieve lattice-misfit-related strain by partial lateral relaxation towards their bulk lattice constant. This would not be possible for a flat and continuous film. Now the microrough surface is energetically favored and the influence of the growth kinetics is therefore observed in an increase of the roughness with temperature. Strain-relieving defects are generated at a coverage of ∼12 ML and finally lead to heavily defected films consisting of small-angle mosaics.

Infrared and Raman measurements were carried out on a-${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sn}}_{\mathit{x}}$:H thin films grown on Si substrates. The hydrogen concentration is found to decrease with increasing tin content. Preferential formation of monohydride groups (GeH) is observed with increasing Sn concentration. The tin dependence of the GeH and ${\mathrm{GeH}}_2$ stretching is explained as being due to the lower electronegativity of Sn in comparison to that of Ge. The study reveals that the stability-ratio electronegativity of germanium should be smaller than 3.59 for the a-Ge:H system. Also, the GeH wagging and ${\mathrm{GeH}}_2$ roll modes show that there is a large bond-angle variation with increasing Sn concentration. Additionally, the changes in the frequency, width, and intensity of the Ge-Ge (TO)-like phonon, clearly indicate that the structural disorder increases with increasing tin content. Auger-electron microprobe and Raman studies with different excitation laser lines show differences near the surface in comparison to the bulk, which are produced by the partial segregation of tin atoms, formation of Sn clusters in the surface, and reduction of the germanium concentration near the surface, as well as preferential attachment of hydrogen to Ge rather than to Sn.