The band structure of SnGe in the zinc-blende structure is calculated using the scalar-relativistic linear-muffin-tin-orbital method in conjunction with the density-functional scheme. The local-density approximation is empirically corrected by means of an external potential. Special emphasis is placed on the effects of inversion asymmetry, such as ionicity and spin splittings. An equilibrium volume is found at a lattice constant of ${\mathit{a}}_0$=6.0630 Å, which is very close to the average of the lattice constants of Ge and α-Sn. At the corresponding volume, the calculated direct gap is +0.085 eV. For a slightly larger lattice constant, corresponding to the average volumes of the two constituents, SnGe should have a gap ‘‘negative’’ of nearly the same magnitude, and thus have an inverted band structure similar to α-Sn. The polarity of the Ge-Sn bond is calculated to be lphap = 0.2—. The transverse effective charge is eTtar = 0.47—, Sn being positive (‘‘cation’’).

We have studied the electronic and structural properties of the antifluorite compounds ${\mathrm{Mg}}_2$X (X=Si, Ge, Sn), ${\mathrm{Be}}_2$C, and hypothetical compounds ${\mathrm{Mg}}_2$C and ${\mathrm{Be}}_2$Si using the first-principles pseudopotential total energy method. Five of the compounds are small-gap semiconductors, while ${\mathrm{Be}}_2$Si is a metal. Calculated lattice constants agree well with experiment for the four known compounds, but are consistently a few percent smaller than the reported values. The bulk moduli of this group of materials follow a semiempirical formula for ${\mathit{B}}_0$ to within ∼5%. Bulk moduli calculated from first principles, corrected for the underestimation of the lattice constant, agree well with the available experimental values.

We have investigated the microwave photoconductivity of 100-μm- and 50-μm-wide Hall bars fabricated from GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructures. We found resonant responses at frequencies ${\mathit{f}}_{\mathrm{res}}$ with ${\mathit{f}}_{\mathrm{res}}^2$(B)=${\mathit{f}}_{\mathrm{res}}^2$(B=0)+${\mathit{f}}_{\mathit{c}}^2$, where ${\mathit{f}}_{\mathit{c}}$ is the cyclotron frequency of the two-dimensional electron gas in the perpendicularly applied magnetic field B. This shows that the photoresponse is dominated by collective plasmon excitations confined within the width of the Hall structure.

Spectral lines of photoluminescence in ${\mathrm{ZnSe}}_{\mathit{x}}$${\mathrm{Te}}_{1\mathrm{-}\mathit{x}}$/ZnTe single quantum wells (QW)’s are studied experimentally and theoretically. Special attention is given to the linewidth as a measure of the QW quality. The analysis of band offsets shows that the structures under study are type-II QW’s, where electron levels are quantized inside a QW, whereas holes are situated in the barriers. The spectral linewidth depends rather slightly on the thickness of QW’s, ruling out fluctuations of QW thickness as the dominant broadening mechanism. On the other hand, the theory of line broadening by compositional disorder fits the experimental data well without any adjustable parameters, suggesting that it is the compositional disorder that dominates the line broadening in these systems.

The collective plasmon-polariton excitations in finite Fibonacci semiconductor superlattices, which are subjected to a static magnetic field applied parallel to the interfaces, are studied by using local-field theory with retardation. We find that for a given in-plane wave vector, the discrete modes are composed of pseudobands and show rich self-similar patterns. The dispersion relations of the modes are obviously modified by the application of the magnetic field, and the propagation of the surface waves shows remarkable nonreciprocal behavior in the field. A number of coupled guided modes are found when the retardation effects are taken into account. We plot the profiles of the amplitudes to investigate the localization properties of the polaritons. The results show that those modes isolated from the pseudobands are localized, the modes located in the pseudobands are extended, while those located at the edges of the bands are critical.

The interpretation of photoemission-spectromicroscopy studies of Au on GaSe requires a revision of established ideas about this interface, which has long been considered a prototype of Schottky-like systems. We find that the interface-formation process involves strong substrate-overlayer interactions, the release of free Ga, and the formation of interface species, and leads to a barrier height in total disagreement with the Schottky model. Furthermore, the space-resolving capabilities of our instruments revealed lateral inhomogeneities of the local overlayer thickness and of the local band bending.

Landau-level oscillations are observed in the photoluminescence from an ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs single heterojunction in an applied magnetic field. Extrapolating the oscillations back to zero field gives the energy of the transition from the two-dimensional (2D) electrons to the free heavy holes (hh1 and hh2) and free light holes (lh) weakly confined in the GaAs active layer. The measured energy separation between hh1 and lh is 1.8 meV, which agrees very well with the calculated value of 2.2 meV. The measured energy separation between hh1 and hh2 is 3.8 meV, in good agreement with the calculated value of 4.4 meV. The 2D electron effective mass was determined to be ${\mathit{m}}_{\mathit{e}}^{\mathrm{*}}$=0.086m. The light-hole effective mass was determined to be ${\mathit{m}}_{\mathrm{lh}}^{\mathrm{*}}$=0.078m, using the GaAs heavy-hole effective mass ${\mathit{m}}_{\mathrm{hh}1\mathrm{}}^{\mathrm{*}}$=0.46m as input. The effective mass ${\mathit{m}}_{\mathrm{hh}2\mathrm{}}^{\mathrm{*}}$ is approximately the same as ${\mathit{m}}_{\mathrm{hh}1\mathrm{}}^{\mathrm{*}}$.

Vibrational Raman scattering and x-ray diffraction have been performed on GaSb/InAs superlattices. The composition of the ${\mathrm{As}}_{\mathit{x}}$${\mathrm{Sb}}_{1\mathrm{-}\mathit{x}}$ plane that connects the InAs and GaSb layers has been varied by controlled growth techniques. When x is equal to 0 or 1, the InAs and GaSb layers are connected with InSb or GaAs bonds, respectively. Planar vibrational modes (PVM’s) localized at the interface are observed. The energies of the GaAs-like and InSb-like PVM’s are studied as a function of x and are compared with results of a random-element isodisplacement model.

Hall mobility, Hall-to-drift mobility ratio, and the magnetoresistance coefficient of the two-dimensional (2D) electron gas in a square quantum well of GaAs are calculated in the temperature range 4–40 K in the framework of Fermi-Dirac statistics. Carrier scattering via screened deformation potential acoustic, piezoelectric, and ionized impurity interactions are considered. The variation of the galvanomagnetic coefficients is studied with lattice temperature, 2D carrier concentration, channel width, and the magnetic field in the classical region. Our calculated mobilities agree well with the available experimental data. The magnetoresistance coefficient is found to be quite sensitive to the change of the system parameters.

The electronic properties of twinning boundaries, stacking faults, and a recently proposed structure, the twinning superlattice, in group IV and III-V diamond-type and zinc-blende-type semiconductors are calculated and discussed.

The rates of electron scattering by acoustic phonons in a rectangular quantum wire embedded into another material are calculated in the framework of the Fermi golden rule. Both intrasubband and intersubband electron scattering by acoustic phonons are considered. It has been shown that due to uncertainty of momentum conservation in quasi-one-dimensional systems the acoustic-phonon scattering becomes essentially inelastic in contrast to that in bulk materials. The acoustic-phonon scattering rate in quantum wires increases with the decrease of cross section of the wire and is much greater than that in bulk materials. It is shown that the correct treatment of inelasticity leads to a nonmonotonic dependence of the emission rate on electron energy and to the disappearance of the divergency of the acoustic-phonon scattering rate at the bottom of each subband. Therefore, the scattering time averaged over the distribution function exceeds considerably that calculated using elastic and quasielastic approaches where the scattering rate is divergent. We demonstrate that electron mobility at temperatures less than 100 K calculated within elastic or quasielastic approximations is greatly underestimated.

First-principles density-functional calculations of the electronic properties of ZnS/ZnSe (001) strained-layer superlattices are used to investigate the influence of hydrostatic pressure on the valence-band offset (VBO). Three different strain modes corresponding to various values of the relative thicknesses of the two types of layers are considered. The pressure coefficients of the VBO’s are found to be very sensitive to the strain mode. A I→II type conversion associated with the conduction-band crossover between the ZnSe well layers and ZnS barrier layers is found, in agreement with recent experimental data. The pressure behavior of the key quantities (VBO’s, bulk moduli, energy gaps) is discussed for various strain modes.

An analytical expression for shot noise in a correlated sequential tunneling current has been derived by solving the master equation exactly, with the Pauli correlation as a special case. Our theory is applied to the Coulomb-blockade single-electron tunneling system with two tunnel junctions. Given capacitances and resistances of the system, the temperature dependence and the bias-voltage dependence of the noise spectrum in the entire range of frequency have been analyzed in detail. We have demonstrated that the noise spectrum is more sensitive to the bias voltage than is the current itself to the voltage. Therefore, noise spectroscopy is a much more accurate tool to investigate the correlation in tunneling transport through ever smaller multiple-junction structures.

The high-frequency response of resonant tunneling devices (RTD’s), subjected to a time-dependent signal, is considered in two different situations when operating in the negative-differential-resistance (NDR) region: stable and unstable. The study of this behavior is considered from three different approaches, all based on the phase-space distribution-function formalism. In the stable case, the equivalent-circuit approach (ECA) is deduced from the published numerical results obtained by one of us (FB. and collaborators) dealing with the complex dynamical aspects in phase space of quantum transport in RTD, operating at dc bias in the NDR region of its ideal characteristic current-voltage (I-V) curve. The ECA is found to be very useful in resolving the various outstanding controversies concerning the dynamical quantum transport behavior of RTD. For unstable operation in the NDR region, nonperturbative approaches are more appropriate. Here, a time-dependent transformation of phase space is found which transforms the quantum distribution (QDF) transport equation to the same form as that in the absence of a time-dependent signal. This time-dependent transformation is useful when the applied time-dependent electric field is assumed to be position independent. In a more general and realistic situation, an applied time-dependent voltage at the drain will self-consistently lead to a time-dependent and position-dependent potential inside the device. For this general situation, we introduce two different representations of quantum transport, namely, the Liouville representation and the phase-space fluid representation. The QDF solution has inherent undesirable features for studying the dynamics of phase space, which can be eliminated by special processing. This processing yields the positive definite Husimi distribution. It is suggested that the use of the Husimi distribution enables a microscopic dynamical viewpoint of ECA as well as shedding further light on the dynamical nature of the quantum inductance.

The complex reaction path of the dissociative chemisorption of ${\mathrm{Sb}}_4$ on Si(001) involving four distinct types of precursor states is determined using a direct ‘‘tracking’’ method with scanning tunneling microscopy. The energy barriers and the prefactors for the transitions between different states are measured by analyzing the population distribution of Sb clusters as a function of thermal treatment. These precursors are found not to have thermal mobility before dissociation, contrary to the widely held notion about precursor states.

A Hall–Van der Pauw and high-field magnetotransport study is reported on ${\mathrm{GaInP}}_2$ epilayers, which contain naturally ordered regions with lower band gap than that of the embedding disordered regions. Below T=200 K three conductivity mechanisms are distinguished in this material: hopping conduction with activation energy ${\mathrm{\epsilon }}_3$ dominates for T<30 K, band conduction with activation energy ${\mathrm{\epsilon }}_1$ for T>85 K, and ${\mathrm{\epsilon }}_2$ conduction at intermediate temperatures with activation energy ${\mathrm{\epsilon }}_2$. The behavior of the conductivity σ in a transverse magnetic field B is found to be in good agreement with theory. The activation energy ${\mathrm{\epsilon }}_2$ shows excellent quadratic dependence on B, and the preexponential factor ${\mathrm{\sigma }}_3$ is proportional to exp(-const${\mathit{B}}^{0.54\pm 0.04}$). Mobility data above T=200 K show unprecedented proof of cluster scattering: calculations based on the Harrison-Hauser/Marsh formalism revealed cluster radii of 3.5 nm and provided absolute values for the fractions of the crystal volume occupied by ordered clusters.

A systematic experimental study of confinement effects on the strength of electron–optical-phonon interactions is presented. The hydrogenic 1s-2${\mathit{p}}_{+1\mathrm{}}$ transition of shallow donors in bulk GaAs and GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells (MQW) and superlattices has been tuned through resonances with the GaAs optical phonons by magnetic fields up to 23.5 T and followed with far-infrared photoconductivity spectroscopy. Extremely large and asymmetric interaction gaps have been observed in both two-level and three-level resonance regions for small-well-width (125 Å) MQW samples. These gaps decrease systematically as the well width increases, approaching the bulk limit for the largest-well-width (450 Å) sample. For the superlattice sample (80-Å well and 9-Å barrier), the interaction is stronger than that for bulk, but much smaller than that for the MQW samples with comparable well width. Results are consistent with enhancement of the interaction as confinement progresses from three dimensions to two dimensions and demonstrate that the extent of the electronic wave function is the most important factor determining the interaction strength. Other phonon modes (interface phonons) may also contribute to the enhanced interaction for small-well-width samples. The 1s-3${\mathit{p}}_{+1\mathrm{}}$ transition was also used to study the resonant polaron effects for strong-confinement MQW samples; results are consistent with those from the 1s-2${\mathit{p}}_{+1\mathrm{}}$ transition.

Low-energy ${\mathrm{D}}^{+}$ scattering has been employed to explore the nature of the bonding of Na, K, and Cs adatoms on the Si(100), Ge(100), ${\mathrm{TiO}}_2$(110), Pt(111), and ${\mathrm{SiO}}_2$ surfaces in a low-coverage regime (<1.7×${10}^{14}$ adatoms/${\mathrm{cm}}^2$). The analysis, based on neutralization and inelastic scattering of the ${\mathrm{D}}^{+}$ ions, reveals that the alkali-metal adatoms are essentially neutral with significant covalency on the Pt(111) surface while those except for Na are ionized on the semiconductor surfaces. The charge state of Na is critical and we conclude that large ionicity occurs only on the ${\mathrm{TiO}}_2$(110) surface. The special nature of the Na charge state on the semiconductor surfaces is caused by a larger ionization energy for Na than for the other alkali-metal adatoms.

At the energies of interest in x-ray photoelectron spectroscopy (XPS), total external reflection of the x-ray beam occurs from a smooth surface at small incidence angles. The penetration of the x rays into the material is strongly attenuated at these angles and surface sensitivity is enhanced in the XPS yields. As the incidence angle is increased, the x rays penetrate more deeply into the material and the XPS signal contains a larger contribution from the bulk. By exploiting this angle-dependent x-ray penetration depth, it is possible to obtain depth-dependent XPS spectra from which the concentration profiles of the photoelectron-emitting atoms can be inferred. In this paper we develop a general formalism for calculating grazing-incidence XPS (GIXPS) yields from multilayer media. A quantitative analysis of GIXPS spectra acquired from an oxidized GaAs(100) surface that was annealed to remove oxidized As will be discussed. The results show that this annealed oxide is composed of ${\mathrm{Ga}}_2$${\mathrm{O}}_3$ and that the oxide-GaAs substrate interface is rough.

A semiempirical tight-binding theory of energy bands in rhombohedral A7-structure crystals is developed and applied to three group-V semimetals: arsenic, antimony, and bismuth. A general description of the method is explicitly given, including the matrix elements of the tight-binding Hamiltonian, and the treatment of the spin-orbit interaction which is noticeable in Bi. For each of these materials the theory uses 15 parameters, obtained in accord with a third-neighbor model which includes the spin-orbit coupling, to reproduce the major features of the band structures. The determination of these parameters is made by fitting the existing pseudopotential and ab initio data for the band structures at some high-symmetry points of the Brillouin zone. Comparison with first-principle calculations and experiments gives very good agreement throughout.