We have investigated the general trend of solid solubility (SS) of magnetic ions in diluted-magnetic-semiconductor (DMS) materials. The SS’s of Fe and Co in CdSe are found to be 0.24 and 0.11, respectively. We have also observed that the SS of magnetic ions in some systems of DMS materials shows a linear relationship to the product of the electronegativity ratio of magnetic ions to host cations and the ratio of the magnetic ion-anion bond length to the host cation-anion bond length. From this observation, it is argued that the SS of magnetic ions can always be expressed by a single stress parameter defined as Υ=(ΔX+1)(Δd+1) in ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$Se (M=Mn, Fe, and Co) crystals. And the critical stress that the natural crystal structure of the host semiconductor must sustain is observed to be strongly related to the relative size of the anion to the cation in ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$B (B=S, Se, and Te) DMS material systems.

Transport properties of electrons in antidot superlattices are studied in Si/Ge heterostructures. Lateral superlattices with periods between 830 and 500 nm were imposed upon high-mobility two-dimensional electron gases in Si/${\mathrm{Si}}_{0.7}$${\mathrm{Ge}}_{0.3}$ heterostructures by means of laser holography and reactive ion etching. Typical features known from GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As samples, such as low-field commensurability oscillations in the longitudinal resistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$, additional nonquantized Hall plateaus, and quenching of the Hall effect around B=0, are observed. From the position of the commensurability maxima in ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$ we conclude that the lateral potential is rather smooth.

A magnetoresistance peak at zero magnetic field due to coherent backscattering is studied in submicrometer quantum dots with quantum-point-contact leads. A systematic series of experiments on ballistic microstructures shows that coherent backscattering is distinct from conductance fluctuations at finite fields and gives properties in agreement with semiclassical theory. The effect results from interference between pairs of time-reversed paths of ballistic electrons scattered from the walls of the dot, analogous to weak localization in diffusive systems.

The effect of inelastic scattering is calculated for a model system with two alternate paths to the final states. It is found that an inelastic event in either path eliminates completely the alternate path, rather than simply randomizing the relative phase for the two paths. The elimination of the second path occurs through a factor of the zero overlap between the ground-state and excited-state wave functions of the oscillator that is excited. A phase randomization would also eliminate interference between the two paths, as does the elimination of the alternative path. However, an assumed randomizing of the phase does not predict the correct correlation between the electronic and oscillator final states for this model system.

One-dimensional quantum-wire systems are peculiar in the sense that binary electron-electron collisions cannot thermalize the energy distribution of the electrons in the same subband. We show that such a thermalization occurs through many-body Coulomb scattering. We consider a one-dimensional electron gas described by Newton’s equations of motion with many-body Coulomb forces. These equations are solved by the molecular-dynamics technique. Thermalization of the nonequilibrium distribution function towards Maxwell’s function is demonstrated for a single-subband GaAs wire with electron density 1×${10}^5$ ${\mathrm{cm}}^{\mathrm{-}1}$–3×${10}^5$ ${\mathrm{cm}}^{\mathrm{-}1}$ and electron temperature 200 K.

We solve an exact model of two-dimensional resonant tunneling through a potential barrier with a point defect. The model shows that the scattering amplitude has a very narrow spreading angle, and gets its maximal value for a small incoming angle. Even when the incoming wave is a narrow beam of electrons, the transmission coefficient depends very strongly on the position of the impurity. This characteristic can be used to detect the position of an impurity (or defect) in a two-dimensional layer.

We suggest a method to measure the Compton wavelength by placing a superlattice in combined static electric and magnetic fields applied along its growth axis. When the magnitudes of the fields are appropriately chosen, a resonance can be excited between the transverse (circular) and longitudinal (oscillatory) motion of the carriers in the superlattice. This resonance enables an accurate measurement of the Compton wavelength.

The localized states which appear in a superlattice as a result of thickness variations of barriers or quantum wells are calculated in the framework of the tight-binding approximation. We obtain very simple formulas in terms of single-quantum-well parameters. There is always a localized state for an enlarged or narrowed quantum well. Two localized states exist in the case of decreased barrier thickness. The range of validity of the formulas is discussed as a function of the superlattice period.

In this work, we have numerically integrated in space and time the effective-mass Schrödinger equation for an exciton in a semiconductor structure. Considering a Coulomb interaction between the electron-hole pair in a triple quantum-well system, we have obtained a time-varying dipole moment in the heterostructure with an amplitude which is also oscillating with time. In this way, we have shown the possibility of having another kind of terahertz electromagnetic radiation emerging from a semiconductor device after an optical excitation of the sample.

The quantum-well localized states are determined for the two-band model, using the method of approximate canonical transformations in the Luttinger-Kohn representation. The results are compared with the predictions of the conventional method, as well as with experiment.

We calculate exactly, using finite-size techniques, the quantum mechanical and many-body effects to the self-capacitance of a spherical-shell quantum dot, i.e., the motion of electrons is confined to the surface of the dot, in the regime of extreme confinement, where the radius of the sphere is much smaller than the effective Bohr radius. We find that the self-capacitance oscillates as a function of the number of electrons close to its classical value. We also find that the electrostatic energy as a function of the number of electrons extrapolates to zero when N=1, suggesting that the energy scales like ${\mathit{e}}^2$N(N-1) instead of (Ne${)}^2$. We also provide evidence that the main deviations from the semiclassical description are due to the exchange interaction between electrons. This establishes, at least for this configuration, that the semiclassical description of Coulomb charging effects in terms of capacitances holds to a good approximation even at very small scales.

We report magnetoluminescence investigations of undoped ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs single quantum wells. At the highest available magnetic fields (11 T) the excitonic recombination shows well resolved spin splittings. For low indium content the splitting is dominated by the heavy-hole valence-band splitting as confirmed experimentally. The theoretical analysis allows us to determine the electron as well as the heavy-hole g values in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As on GaAs within the composition range 0<x<0.27 for quantum well thickness ${\mathit{L}}_{\mathit{z}}$>120 Å.

The transmittance and reflectance spectra of PbTe films grown on different substrates (KBr, KCl, ${\mathrm{BaF}}_2$) by the nonequilibrium growth technique of laser-assisted deposition are investigated. The films represent two-layer structures: the sublayer, adjacent to the substrate, consists of the high-pressure metastable CeCl-type phase while the upper sublayer is of the stable fcc phase. As the metastable-CeCl-type-phase lattice volume depends on the substrate nature, we investigate PbTe films with CsCl-type phase corresponding to different pressures. The optical energy gaps in the various films are determined from the maxima in the refractive index dispersions, calculated from the transmittance and reflectance spectra. Thus, the energy-gap pressure coefficient in the PbTe CsCl-type metastable phase is obtained.

An intense longitudinal-surface-phonon resonance in addition to the Rayleigh mode is observed on Ag(001) by inelastic helium-atom scattering (HAS). This mode, which is only barely visible by electron-energy-loss spectroscopy, is similar to the one previously detected by HAS for Cu(001). This observation provides additional evidence for the pseudocharge model previously invoked to explain the anomalous longitudinal resonance observed in several metal surfaces by HAS. The observed differences between Cu(001) and Ag(001) are also shown to be consistent with the pseudocharge model.

The fractal dimension of films formed by random deposition of particles onto a surface was investigated by means of computer simulation. Unit-square particles are deposited randomly onto a one-dimensional lattice of unit cells, forming clusters. The relation between the density of particles, proportional to the thickness of the film, and the fractal dimension of the clusters was obtained for a static case of a constant average density of particles. The results show that the fractal dimensions are less than one in agreement with Tanaka’s quantitative predictions. For small densities of particles the dimensions are significantly less than one, while for larger clusters the dimensions tend to unity and the fractal properties disappear.

An efficient semiempirical molecular-dynamics technique to treat interactions in transition metals is introduced. The method is based on the tight-binding scheme incorporating d delectrons. Optimized geometries are obtained using this scheme for ${\mathrm{Ni}}_{\mathit{n}}$ clusters for n up to 10. The expected general trends for the various cluster properties are well described by our results. Important qualitative differences from semiconductor clusters are observed. The technique appears to be promising in modeling interactions in alloys containing semiconductor and metal atoms.

We review the x-ray-diffraction and high-resolution transmission electron microscopy (HRTEM) data that Doll et al. [Phys. Rev. B 43, 6816 (1991)] used as evidence for the epitaxial growth of cubic boron nitride (cBN) on silicon (001) surfaces. The three reported x-ray-diffraction peaks do not provide unambiguous evidence for cBN due to potential interference from the graphitelike phase of BN and from artifacts of the silicon substrate. We provide an interpretation of their HRTEM image. Our interpretation does not provide support for an epitaxial cBN/Si relationship or the presence of cBN.

In ferroelectric perovskites, the strong spontaneous polarization is due to giant values of the Born effective charges, which are much larger than predicted on the basis of the nominal ionicity: we investigate the physical origin of such charges, which by definition measure the current traversing the sample during polarization reversal. Our first-principles calculations for ${\mathrm{KNbO}}_3$ identify unambiguously the dominant mechanism with the presence of covalent bonding. The giant charges are reduced to their nominal values in a computational experiment performed on a fake material, where covalence has been artificially suppressed.

We report the high-resolution temperature-dependent photoemission spectra of FeSi. We measure an extremely small gap of less than 5 meV in contrast to electrical-resistivity, magnetic-susceptibility, and optical-conductivity measurements, which show an activation energy of about 60 meV. The difference in the gap value is attributed to localized states near the Fermi level, which effectively increase the activation energy associated with a charge or spin excitation as observed in conductivity and susceptibility studies. The density of states at the Fermi level increase systematically on increasing temperature and result in a transition to a metallic phase at 300 K. The data suggest that localization effects play an important role in the ground-state properties of FeSi.

We report measurements of the longitudinal field-dependent muon-spin relaxation rate (${\mathit{T}}_1^{\mathrm{-}1}$) in n-type Si and GaAs under conditions where coherent spin precession of muonium is unobservable. A peak in ${\mathit{T}}_1^{\mathrm{-}1}$ as a function of magnetic field is observed and shown to be characteristic of neutral bond-centered muonium (${\mathrm{Mu}}_{\mathrm{BC}}^0$) experiencing spin-exchange scattering with free carriers. These results establish that neutral ${\mathrm{Mu}}_{\mathrm{BC}}^0$ does not convert to negatively charged muonium in n-type Si below approximately 200 K and is present in metallic n-type GaAs:Si at 5.5 K.