We have investigated the electronic structures of the valence bands of β’-AgMg (CsCl structure) and α’-${\mathrm{Ag}}_3$Mg (${\mathrm{DO}}_{23}$ structure) by a combination of ultraviolet and x-ray photoelectron spectroscopies and first-principles band-structure and photocurrent calculations. The overall agreement between the measurements and calculated results is good indicating that the one-electron approach provides a realistic description of the electronic structure in Ag-Mg ordered alloys. We also present results for the core-level shifts observed on alloying.

We study the structural and electronic properties of various polytypes of SiC through self-consistent ab initio pseudopotential calculations. For the wurtzite (2H), 4H, and 6H structures, the equilibrium lattice constants and bulk moduli are very similar to those for the cubic structure. The energies calculated for the polytypes considered here are very close to within 4.3 meV/atom, which may explain the polytypism of SiC. The 4H structure is found to be lowest in energy because of the attractive interactions between the alternating cubic and hexagonal stacking layers, while the wurtzite structure is most unstable among the polytypes. We find the asymmetric charge distribution for a Si-C bond to be on the boundary separating the zinc-blende and wurtzite phases, which should be related to the polytypism of SiC. In the hexagonal polytypes, the M conduction-band energy increases, while that of the K point decreases as the hexagonal close packing becomes more prominent. Thus, the conduction-band minimum state located at the X point for cubic SiC changes to the M point, and then to the K point for the 2H structure. For the cubic structure, the density of states near the conduction-band edge increases slowly with energy, while it shows very rapidly increasing behavior for the 6H polytype because its conduction-band edge states are flattened due to the band folding and the energy-increasing behavior of the M state when the hexagonal-close-packing nature is enhanced.

The impact ionization rate and its orientation dependence in k space is calculated for GaAs. The numerical results indicate a strong correlation to the band structure. The use of a q-dependent screening function for the Coulomb interaction between conduction and valence electrons is found to be essential. Comparison with recent results for Si, GaAs shows a harder threshold behavior. A simple fit formula is presented for easy calculation of the direction-dependent transition rate. With only the band structure as input the numerical results are closely reproduced in an arbitrary direction in the Brillouin zone.

We propose a model to describe temperature-dependent electronic transitions using an effective electron-ion interaction. We present a nonperturbative calculation of the temperature dependence of the forbidden energy gap of CdTe crystals. The results are compared with similar calculations using the statistical-function method and both give good agreement with experimental data. It is also demonstrated that the thermal expansion of the lattice plays a minor role for the temperature variation of the electronic energy levels.

The optical band gap of the filled tetrahedral semiconductor LiZnN [viewed as a hypothetical zinc-blende (ZnN${)}^{\mathrm{-}}$ lattice partially filled with He-like ${\mathrm{Li}}^{+}$ interstitials] was studied. The band-gap nature of LiZnN predicted theoretically by an ‘‘interstitial insertion rule’’ is confirmed to be direct with a forbidden gap of 1.91 eV at room temperature. The band gap is closer to a value calculated using a nonrelativistic augmented-spherical-wave method rather than that predicted from the empirical trend of band gaps between the filled tetrahedral (LiZnAs and LiZnP) and zinc-blende (GaAs and GaP) structures. The difference on the bonding character between the filled tetrahedral and zinc-blende compounds is discussed.

Relaxation of thermal-remanent magnetization and isothermal remanent magnetization of spin glass in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te diluted magnetic semiconductors have been studied at different conditions. Magnetization relaxation can be described by a power-law decay, M(t)=${\mathit{M}}_0$${\mathit{t}}^{\mathrm{-}\mathrm{\alpha }}$ (t>${\mathit{t}}_0$ and ${\mathit{t}}_0$=2 s) with small values of α or a logarithmic decay M(t)=${\mathit{M}}_0$(1-α lnt) (t>${\mathit{t}}_0$ and ${\mathit{t}}_0$=2 s). Temperature and applied magnetic-field dependencies of the decay parameter α have been measured. The above-band-gap photoexcitation has been used to generate free carriers (electrons and holes) in the sample and their effects on the spin-spin interaction of Mn ions have been studied. The dependence of the power-law decay parameter α on excitation light intensity has also been measured. It is found that α is proportional to the photogenerated carrier concentration. Furthermore, aging effects in the spin-glass state have also been studied by varying the time duration of the applied magnetic field. The transient responses of magnetization in the spin-glass state upon applying a magnetic field in the dark and under illumination have been measured and are found to follow a power-law time dependence, M(t)=${\mathit{M}}_0$+${\mathit{M}}_1$${\mathit{t}}^{\mathrm{\beta }}$. Temperature and the applied magnetic-field dependencies of the transient parameter β have been measured. A mechanism, involving an increased spin domain size under light illumination via free-carrier-Mn spin interaction, can explain our results very well.

We present the results of an extensive ab initio study of the Σ=5 tilt [310] grain boundary in germanium. We find that the boundary reliably reconstructs to the tetrahedrally bonded network observed in high-resolution electron microscopy experiments without the proliferation of false local minima observed in similar twist boundaries. The reduced density of bonds crossing the grain-boundary plane leads us to conjecture that the boundary may be a preferred fracture interface. Though there are no dangling bonds or miscoordinated sites in the reconstruction, the boundary presents electron-trap states just below the conduction band. Further, we show that lattice relaxation effects are irrelevant to the segregation of impurities to tetrahedrally reconstructed defects and that the interfacial electron-trap states give rise to an electronic frustration mechanism that selectively drives the segregation of only n-type dopants to the boundary.

A formula for frequency-dependent optical second-harmonic susceptibilities for insulating crystals, including local-field corrections, is presented. In analogy to a formula given previously for the static limit, the formula is analyzed in terms of ‘‘virtual electron’’ (ccv) and ‘‘virtual hole’’ (vvc) terms to obtain a numerically stable form. Numerical results for GaP and GaAs agree with most of the experimental values suggested in a recent review article by Roberts. Miller’s ${\mathrm{\Delta }}_{\mathit{M}}$ is predicted to vary by 13% from the laser lines at 10.6 to 1.32 μm for GaP.

Tails in the density of electron states in diluted magnetic semiconductors are examined theoretically. The exchange interaction between a charge carrier and magnetic ions makes the energy dependence of the density of states in the tails markedly different from those known for nonmagnetic solid solutions. The cases of uncorrelated and strongly correlated disorder are analyzed. In both cases the density of states in the tail turns out to be nonmonotonic. In the case of uncorrelated disorder the density of states has a gap, while it possesses a deep valley in the case of strongly correlated disorder. The thermal disorder in the spin system of the ions makes the density of states temperature dependent. Some possible experimental manifestations of these features of the tails in diluted magnetic semiconductors are discussed.

Electronic band structures, equilibrium lattice constants and structural parameters, cohesive energies, and bulk moduli calculated by means of the linear-muffin-tin-orbital method are presented for ${\mathrm{BeCN}}_2$, ${\mathrm{MgCN}}_2$, ${\mathrm{BeSiN}}_2$, ${\mathrm{MgSiN}}_2$, and ${\mathrm{MgSiP}}_2$ in the chalcopyrite structure. The relationships of these compounds to the ‘‘parent’’ III-V compounds are clarified.

We present theoretical studies of phonon modes of undoped ${\mathrm{HgI}}_2$ in its red tetragonal form. A rigid-ion model including the Coulomb interaction is used which gives the best fit to the neutron scattering, infrared reflectivity, and Raman scattering data. The calculated sound velocities are also in accord with experiment.

Transport properties of direct-gap semiconductors are calculated in order to find the best thermoelectrics. Previous calculations on semiconductors with indirect band gaps found that the best thermoelectrics had gaps equal to ${\mathit{nk}}_{\mathit{B}}$T, where n=6-10 and T is the operating temperature of the thermoelectric device. Here we report similar calculations on direct-gap materials. We find that the optimum gap is always greater than 6${\mathit{k}}_{\mathit{B}}$T, but can be much larger depending on the specific mechanism of electron scattering.

The Faraday rotation of n-type InSb has been measured for wavelengths between 8.0 and 13.0 μm at 9 K, using magnetic fields up to 150 kG. Measurements were made on samples with nominal carrier concentration of 1×${10}^{14}$, 6×${10}^{14}$, 1×${10}^{15}$, and 5×${10}^{15}$ ${\mathrm{cm}}^{\mathrm{-}3}$. The experimental results have been successfully analyzed in terms of interband and intraband transitions at the Γ point in the Brillouin zone, using a quantum-mechanical treatment. The four-band k⋅p Pidgeon and Brown model was used to calculate the energy levels and the matrix elements for these transitions.

Results are reported of a set of first-principles calculations for hydrogen interacting with bulk Si, the Si surface, and with other impurities and defects in the Si lattice. The total energy values corresponding to the various structures are all expressed with respect to a common reference (the free H atom). The resulting energy diagram provides immediate insight in the relative stability of different configurations. It also allows the derivation of formation energies, which allow calculation of concentrations. Among the topics discussed are hydrogen solubility and desorption from a Si surface.

Acoustic waves of shear horizontal polarization are studied in a finite superlattice (SL) deposited on a substrate with or without a surface cap layer, or sandwiched between two materials. Using a Green’s function method, we have obtained closed-form expressions of local and total densities of states as a function of the frequency ω and the wave vector ${\mathit{k}}_{\mathrm{\parallel }}$ parallel to the layers. Due to the substrate-SL-capping layer interaction, different kinds of localized and resonant discrete modes are found and their properties are investigated.

The existence of mesoscopic conductance fluctuations invalidates the traditional concept of impurity average conductances even for metallic systems which are much larger than the inelastic-scattering length. We use the methodology of classical conductance networks in order to incorporate the effect of mesoscopic conductance fluctuations in a self-consistent extended scheme for computing macroscopic conductances. Scaling ideas are reconsidered with a main emphasis on the two-dimensional disordered electron gas and, in particular, the integral quantum Hall regime. We find that the singularity structures of the theories of ‘‘macroscopic’’ and ‘‘impurity averaged’’ conductances are quite generally the same. Significant numerical differences may occur, however, in the regime of strong quantum interference effects. Specific experimental work on the integral quantum Hall regime is being proposed for the purpose of resolving some of the outstanding questions raised in this paper.

The pressure dependence of the low-frequency dielectric constant of layered gallium sulfide, parallel to the c axis, is investigated through capacitance measurements. The measured pressure coefficient Δ(ln${\mathrm{\epsilon }}_{\mathrm{\parallel }}$)/ΔP is found to be (80±5)×${10}^{\mathrm{-}3}$ ${\mathrm{GPa}}^{\mathrm{-}1}$. This large and positive pressure coefficient is shown to be coherent with models of charge transfer from the Ga-Ga intralayer bond to the interlayer space under pressure.

Amorphous-hydrogenated-silicon double Schottky switching diodes in which one contact is vanadium, formed to produce switching, can show discrete steps in the I-V characteristics in the ON state at resistances of h/2${\mathit{ne}}^2$ where n is an integer. We present experimental data to show that the forming temperature of the device is in excess of 1100 K, which can allow diffusion. Auger-electron-spectroscopy depth profiling shows that the top electrode penetrates significantly into the film in the formed devices, as theorized previously to explain the quantum phenomena. An elemental compositional analysis of the diffused metal region is presented. Resistance plots at various temperatures are consistent with the matrix containing vanadium particles.

The time and temperature dependencies of the double Schottky barriers in semiconducting ferroelectric barium titanate (${\mathrm{BaTiO}}_3$) in the presence of a reducing or an oxidizing atmosphere are considered. Numerical computations of the local variation of barrier heights as a function of time and temperature are presented for both bulk and thin films. Experimental observations and theoretical results are analyzed for donor-doped semiconducting polycrystalline ${\mathrm{BaTiO}}_3$.

Elastic constants of the recently grown nonequilibrium zinc-blende form of MnTe were measured. Strained layer MnTe/ZnTe superlattices in which MnTe appears in this zinc-blende form were studied using triple crystal x-ray diffraction. The diffraction spectra were fitted using a dynamical model to determine the thickness and the lattice constants of each layer. From these and other measurements, the elastic constants ${\mathit{C}}_{11}$ and ${\mathit{C}}_{12}$ of MnTe were determined to be 2.22±0.1 and 1.16±0.1, respectively. These values are very low compared to all other zinc-blende or diamond structure materials investigated so far.