We present here a study of the influence of iron doping on transport and magnetotransport properties of HgSe-based narrow-gap semiconducting mixed crystals, namely ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Se (x≤0.072) and ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se (x≤0.13). The crystals were grown by the Bridgman method. Measurements were performed in the temperature range 1.7–300 K in magnetic fields up to 6 T. For both systems, the electron concentration as a function of increasing concentration of Fe dopants changes in a similar way: it rises proportionally below a certain Fe donor concentration ${\mathit{n}}_{\mathrm{Fe}}^{\mathrm{*}}$ (which depends on the mole fraction x of mixed crystal) and then reaches a constant value (which also depends on x). The electron mobility in samples with ${\mathit{n}}_{\mathrm{Fe}}$>${\mathit{n}}_{\mathrm{Fe}}^{\mathrm{*}}$ shows anomalously high values, similarly to the case of HgSe:Fe studied earlier. We interpret the observed phenomena by assuming that iron dopants create, in the compounds investigated, a resonant donor state with an energy level degenerate with the conduction band continuum. For ${\mathit{n}}_{\mathrm{Fe}}$>${\mathit{n}}_{\mathrm{Fe}}^{\mathrm{*}}$ the system of Fe donors is only partially occupied by electrons, i.e., ${\mathrm{Fe}}^{2+}$ neutral donors and ${\mathrm{Fe}}^{3+}$ singly ionized donors coexist, resulting in a mixed valence regime.

The Coulomb repulsion between the electrons localized on donors leads to a correlation of their positions and results in a dramatic reduction of the scattering rate by ionized impurity potentials. The analysis of the mobility (in the case of ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se also of the Dingle temperature) in terms of the scattering from ionized centers (with the possible spatial correlation of impurity charges taken into account) and the alloy scattering (in the case of ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se also spin-dependent scattering) leads to a fair agreement between the measured data and the theoretical description. The lack of any dependence of the electron concentration upon the level of iron doping in the mixed valence regime (when the Fermi level is pinned to the iron state) enabled us to determine the position of the Fe level as a function of the Zn or Mn mole fraction x. This, in turn, made it possible to estimate the ${\mathrm{\Gamma }}_8$ and ${\mathrm{\Gamma }}_6$ band offsets (denoted W and V, respectively) between HgSe and MnSe and between HgSe and ZnSe. The values determined by us are, in the ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Se system W=-0.5 eV and V=2.6 eV, and in the case of the ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se system W=-1.2 eV and V=3 eV. Moreover, it is noted that even weak Fe doping (corresponding to ${\mathit{n}}_{\mathrm{Fe}}$<${\mathit{n}}_{\mathrm{Fe}}^{\mathrm{*}}$) can lead to a substantial improvement of electrical properties of the compounds studied by us. This is particularly clearly seen for ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Se.

The theory of first-order resonant Raman scattering for bulk semiconductors in the magnetopolaron range is developed. The calculations assume a three-band model for the electronic excitations and scattering configuration when the Raman phonon is emitted via an interband deformation potential interaction with lattice vibrations. The resonant polaron coupling occurs through both, Fröhlich and deformation potential mechanisms. In the polaron range the incoming and outgoing resonances split into doublets, with the relative intensity and width being strongly dependent on laser frequency. The difference in the amplitude and width of the components in each doublet follows from the different weight of the nonrenormalized electron or hole states in the upper and lower branches of the renormalized excitations, and from the larger broadening of the upper branch.

Auger-electron spectroscopy, Auger depth-profile analysis, as well as photoelectron spectroscopy give clear evidence for several stages in the formation of the Ho/CdSe(101¯0) interface. For Ho coverages lower than a critical thickness of ≃1 Å, no reaction or intermixing of the components was found. In the range of intermediate coverages, 2 Å<θ<20 Å, Ho-Se chemical reactions are observed leading to a release of Cd. For higher Ho coverages, θ≥20 Å, this stage changes to a regime that is characterized by considerable Cd segregation and surface metallization. The presence of this metallic Cd layer prevents Ho diffusion and inhibits Ho-Se chemical reaction upon further deposition of Ho.

Powder-x-ray-diffraction measurements on siloxene and calculations of the diffraction patterns for the three commonly proposed structures of siloxene (${\mathrm{Si}}_6$${\mathrm{H}}_6$${\mathrm{O}}_3$) clearly show that only a structure with silicon layers is ever observed. The formation of siloxene from ${\mathrm{CaSi}}_2$ is topotactic, with the Si layers remaining intact and with no oxygen insertion into these layers. Siloxene prepared at 0 °C has very little oxygen incorporated into the interlayer gaps, and can be described as hydrogen terminated silicon layers (${\mathrm{Si}}_6$${\mathrm{H}}_6$), which we call layered polysilane. Layered polysilane can be purified by reaction with aqueous HF and is pyrophoric on contact with air. In some sense, layered polysilane can be considered the silicon equivalent of graphite.

Electron-spin-resonance (ESR) measurements have been performed on a series of wurtzite GaN films grown on sapphire substrates by low-pressure metal-organic chemical-vapor deposition. The sample set included films grown with both AlN and GaN buffer layers. The ESR signal results from residual donors with ${\mathit{g}}_{\mathrm{\parallel }}$=1.9510 and ${\mathit{g}}_{\mathrm{\perp }}$=1.9483. The g value and the effective mass can be explained using a five-band k⋅p model. Nuclear hyperfine interactions are observed as a shift in the central resonance position, due to the Overhauser effect from which the density of the wave function at the Ga nucleus is derived. The ESR lines all have quite a sharp Lorentzian shape due to motional narrowing. At low temperatures (T<20 K) the linewidth narrows with increasing temperature, consistent with electrons hopping from donor site to donor site. At higher temperatures the line broadens due to electron-phonon interactions. The concentration of uncompensated donors is independent of film thickness for GaN buffered films but increases monotonically with thickness for AlN buffered films, probably due to a decrease in the concentration of compensating centers. Photoluminescence measurements indicate that only the thickest films are homogeneous along the growth direction.

Magneto-optical and magnetotransport studies have been conducted on a series of strained single ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{In}}_{\mathit{x}}$Sb/GaSb quantum wells grown along [001], [111]A, and [111]B directions by metal organic chemical vapor deposition. Both the interband transition energies and the two-dimensional carrier density show dramatic differences between the three orientations. Self-consistent calculations including the strain-induced piezoelectric field and the effect of band bending have been performed for the [111] structures. Results of the calculations agree very well with the observed dependences on indium content in the wells, well width, and cap thickness. The difference between [001] and [111] samples is due mainly to the presence of the piezoelectric field in the latter. The surface pinning field which is different in both direction and magnitude in the [111]A and [111]B structures contributes to the significant difference in these two orientations for cap thicknesses below 500 Å.

A study of the adsorption of ethylene ${\mathrm{C}}_2$${\mathrm{H}}_4$ on Si(111)7×7 at room temperature by scanning tunneling microscopy and scanning tunneling spectroscopy is reported. No significant change in the surface reconstruction is observed. The spatial distribution of the surface reaction has been analyzed on an atom-by-atom basis. Reacted and unreacted sites have been selectively imaged. A higher reactivity of the adatoms in the faulted subunits with respect to those in the unfaulted subunits is reported. Furthermore, the center adatoms are more reactive than the corner adatoms. On the basis of this distribution of reacted atoms, the adsorption site is assigned. The proposed bond model implies that an ethylene molecule is bonded to a pair of adjacent Si adatom–rest atom. It is also shown that the adsorption process affects not only the surface atoms directly involved in the chemical bond with the ethylene molecules, but also some of the neighboring adatoms.

We investigate experimentally the edge-channel transport in a two-dimensional electron gas confined in a layer structure containing a p-type δ-doped layer parallel to a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure. Due to the concentration gradient induced in the electron gas by the in-grown gate, the innermost edge channel becomes macroscopically wide and couples to an interior contact. For sufficiently large gradients the innermost edge channels can be pushed away from one side of the sample, leading to a total suppression of the Shubnikov–de Haas signal.

We show that a low-intensity femtosecond pulse is severely distorted while propagating through a relatively thin (<7000 Å) GaAs multiple-quantum-well sample and that this pulse distortion depends critically on the dephasing time ${\mathit{T}}_2$ and the total thickness l. An interferometric measurement reveals the existence of well-defined nodes at which the envelope function changes its sign. This pulse distortion significantly affects femtosecond experiments such as pump-probe or four-wave-mixing experiments.

We perform numerical calculations to predict the electronic energy-subband structures in quasi-two-dimensional electronic systems with periodic modulation potentials along the lateral directions under normally applied electric fields. These potentials arise from the periodic modulation of the widths of the systems, such as those produced by deposition of AlAs and GaAs fractional layers on (001) vicinal GaAs substrates. A coordinate transformation was introduced which transforms the systems with periodically structured interfaces to quantum wells with planar interfaces so that the boundary conditions of the electron wave functions are considerably simplified. Far-infrared optical absorptions associated with the electron transitions between the electron conduction subbands of the systems were predicated numerically. The changes of the electronic density of states, energy minigaps, and subband optical-absorption coefficients as functions of the normally applied electric fields are investigated in detail.

Scanning tunneling microscope images obtained after GaAs(110) exposure to ${\mathrm{Br}}_2$ and ${\mathrm{Cl}}_2$ reveal dissociative adsorption and etching at steps and terraces, depending on temperature, fluence, and flux. Exposure at 300 K produces a surface structure with halogen features localized within the rectangle formed by four surface As atoms, having (1×1) symmetry, and with halogen features localized on top of the surface As atoms. Adsorption for substrate temperatures between ∼400 K and ∼525 K results in linear chains along the substrate [001] direction. These chains coalesce with mixed (2×1) and c(2×2) domains. Exposure at 625 K produces volatile Br and Cl products and etching is manifest by single-layer etch pits. Longer exposures at the same flux at 625 K yield a steady-state condition in which five layers are exposed. Etching at 725 K is dominated by single-height-step retreat and triangular double-layer etch pit formation on extended terraces. The nucleation density of double-layer etch pits can be increased and single-height-step retreat can be inhibited at 725 K by increasing the ${\mathrm{Br}}_2$ or ${\mathrm{Cl}}_2$ flux.

The results of the investigation of the fluctuation region of the electron spectrum in a two-dimensional system with a Gaussian white-noise potential and a perpendicular magnetic field are presented. We use the optimal fluctuation method and calculate both the density of states and the localization length in the whole fluctuation region below the lowest Landau level. We describe all possible structures of the quantum fluctuation region and establish limits on the applicability of the white-noise-potential model as well as on the approximation based upon the projection onto the lowest Landau level.

Transport properties of the ν=1/2 state in the presence of tunneling between layers has been investigated. Tunneling induces a resonance pole in the interlayer compressibility. As a result, the ν=1/2 state collapses at temperatures that are of the order of the hopping parameter between the layers. In the absence of tunneling one finds that the density response function for the compressible ν=1/2 state has two different diffusion poles corresponding to a symmetric and an antisymmetric mode.

Photoluminescence spectra of the neutral dense (${\mathit{n}}_{\mathrm{eh}}$<2×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$) magnetoplasma photoexcited in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/InP single quantum wells have been investigated in ${\mathrm{\sigma }}^{+}$ and ${\mathrm{\sigma }}^{\mathrm{-}}$ polarizations. Fine structure of Landau-level transitions has been observed which is caused by the mixture of hole-spin states. A considerable enhancement of electron and hole spin splittings of the zero and first Landau levels arises when the uppermost occupied Landau levels with different spins are unequally filled. An explanation is offered in terms of the exchange inter-Landau-level interactions.

The dispersion relations for optical and acoustic phonons are examined in bulk Si and Ge, Si and Ge strained layers grown on (001) and (111) surfaces, and ultrathin Si/Ge superlattices at ambient pressure and under hydrostatic pressure by using a modified Keating model. This model includes four interactions, which involve up to the fifth-nearest-neighbor atom, and force constants that depend on strain. These strain-modified force constants are related to specific cubic anharmonic terms in the potential energy and also to the empirical parameters p, q, and r that have been used to describe zone-center phonon shifts and splittings arising from strain. This model is used to obtain the mode Grüneisen parameters ${\gamma }_{\mathit{i}}$ throughout the Brillouin zone for bulk c-Si and c-Ge, and explicit analytic expressions for ${\gamma }_{\mathit{i}}$ at the zone center and boundaries. Biaxial strain in the (001) plane is shown to affect phonon dispersion very differently than in previous work that used a much simpler model. For Si and Ge grown on a (111) substrate, the frequency shift due to the biaxial strain for the TO-phonon mode is found to be almost independent of wave vector. The pressure-induced change in the frequency of confined LO phonons in a ${\mathrm{Si}}_{12}$${\mathrm{Ge}}_4$ superlattice predicted by the model agrees with the change measured previously by Raman scattering. This modified Keating model is also used to obtain the second- and third-order elastic constants for Si and Ge.

Successful control of the conductivity of tetrahedrally bonded amorphous carbon (ta-C) by incorporation of N during film growth is reported. N is introduced into the films during growth by injecting ${\mathrm{N}}_2$ gas into a plasma stream formed by a carbon cathodic vacuum arc. X-ray-photoemission-spectroscopy studies of films prepared over a range of ${\mathrm{N}}_2$ partial pressures show that the N concentration varies from 2% to below the detection limit. Spectroscopic studies using electron-energy-loss spectroscopy confirm that the ta-C films with N contents up to 1 at. % retain their predominantly tetrahedral amorphous structure. The as-deposited ta-C, with no intentional N incorporation, is p type with a resistivity of ${10}^7$ Ω cm and an activation energy of 0.22 eV. The addition of N under varying injection levels from ${10}^{\mathrm{-}3}$ to 10 standard cubic cm causes the resistivity to initially go through a maximum at ${10}^9$ Ω cm and then decrease monotonically to 10 Ω cm. A systematic variation of activation energies with increasing ${\mathrm{N}}_2$ flow rate is observed, going through a maximum at about 1.0 eV before decreasing to 0.12 eV. The optical band pseudogap is shown to vary only marginally from the usual 2-eV benchmark. The properties of the doped film can be explained using a simple model of the electronic structure of the tetrahedral amorphous carbon.

Electron mobility in ${\mathrm{Ga}}_{0.47}$${\mathrm{In}}_{0.53}$As quantum wells is calculated for well widths between 2 and 10 nm and for the temperatures of 4.2, 77, and 300 K. Effects of the finite barrier height, energy-band nonparabolicity, mode confinement, electron screening, and degeneracy have been taken into account. The calculated values are found to be close to the experimental results for a well width of 10 nm. Effects of the composition of the barrier layer are also discussed.

High-resolution synchrotron x-ray diffraction from a Si(001) grating surface reveals resolution-limited grating interference peaks around each Bragg reflection. The peaks can be explained by kinematic scattering theory using the concept of a grating form factor. The positions and the intensities of the satellite peaks yield structural information such as the period, the width, and the height of the gratings, as well as its shape and its orientation and registry with respect to substrate lattice, and possible crystal strains.

We describe a technique for the measurement of the diffusivity, solubility, and permeability of ${\mathrm{H}}_2$ through ${\mathrm{SiO}}_2$ thermally grown on Si substrates at room temperature. We have applied this technique to determine the dependence of the ${\mathrm{H}}_2$ permeability on oxide thickness and growth temperature. Since permeability depends strongly on density, these measurements provide a sensitive probe of the oxide density. Our results indicate that the ${\mathrm{H}}_2$ permeability is considerably less in ${\mathrm{SiO}}_2$ films thermally grown on Si substrates than through bulk ${\mathrm{SiO}}_2$, in agreement with previous works which had indicated that thermally grown oxides are denser than bulk ${\mathrm{SiO}}_2$. The permeability is found to decrease with oxide thickness, indicating that thinner oxides have larger densities than thicker oxides. Oxides grown at high temperatures are found to have higher permeabilities than oxides of similar thickness grown at lower temperatures. We present evidence that the dependence of permeability on oxide thickness results from a density gradient throughout the oxide rather than from a uniform reduction of the oxide density as the oxide becomes thicker.

After exposure to hydrogen plasma and chemical etching to remove layers of different thicknesses, n-type GaAs wafers with 〈100〉 and 〈110〉 orientation were deposited with Au to form Au/(n-GaAs) Schottky barriers (SB’s). After zero-bias annealing (ZBA), the Schottky-barrier height (SBH) of the Au/(n-GaAs) SB’s containing hydrogen falls; after reverse-bias annealing (RBA), the SBH rises; and the SBH is reversible within experimental precision in at least three ZBA-RBA processes. Furthermore, the control effect of zero-bias annealing and reverse-bias annealing on the Schottky barrier height depends quantitatively on the orientation of the GaAs wafer and the thickness of the layer removed by chemical etching before deposition of Au. But the Schottky-barrier height of a control Schottky-barrier that is not subject to hydrogen exposure changes little during zero-bias annealing or reverse-bias annealing processes. It is also found that besides the SBH the effective Richardson coefficient of the SB containing hydrogen has a one-to-one correlation with the reverse bias of the RBA (100 °C, 2 h). Experiments strongly support the fact that the hydrogen contained in the SB is essential for the above ZBA-RBA effect. We have suggested a physical model to explain why hydrogen can reduce the Schottky-barrier heights and result in the ZBA-RBA effect of Au/(n-GaAs) Schottky barriers.