We have observed an early stage of agglomeration of self-interstitial atoms in a Czochralski-Si crystal by high-resolution transmission electron microscopy at 450 °C. Based on analyses of the experimental data, it has been suggested that self-interstititals, introduced by electron (300 keV) irradiation, are first arranged along the 〈110〉 direction, forming a linear interstitial defect structure that has no dangling bond in the {110} cross section. After the nucleation, the defect is extended on the {113}-type plane.

The effect of hydrogen-plasma passivation on the optical and electrical properties of gallium antimonide bulk single crystals is presented. Fundamental changes of the radiative recombination after hydrogenation in undoped, zinc-doped, tellurium-doped, and codoped (with Zn and Te) GaSb are reported. The results of optical measurements indicate that passivation of acceptors is more efficient than that of the donors and, in general, the passivation efficiency depends on the doping level. Passivation of deep nonradiative centers is reflected by the gain of photoluminescence intensity and decrease in deep-level transient spectroscopy peak height. Extended defects like grain boundaries and dislocations have also been found to be passivated. The thermal stability of the passivated deep level and extended defects is higher than that of the shallow level. The kinetics of thermally released hydrogen in the bulk has been studied by reverse-bias annealing experiments.

In this paper, recently developed time-convolutionless quantum-kinetic equations for electron-hole pairs near the band edge are used to derive the optical gain and the line-shape function of a driven semiconductor taking into account excitonic effects. The equation of motion for the interband pair amplitude is integrated directly assuming the quasiequilibrium or adiabatic approximation. It is shown that the line shape of the optical-gain spectra is Gaussian for the simplest non-Markovian quantum kinetics. On the other hand, the line-shape function becomes Lorentzian, which has been assumed in most practical calculations, in the Markovian limit. It is also shown that the optical gain is enhanced by (1) excitonic effects caused by the attractive electron-hole Coulomb interaction and (2) interference effects (or renormalized memory effects) between the external driving field and the stochastic reservoir of the system. Gain enhancement by the memory effects can be interpreted as the result of the violation of energy conservation on the time scale shorter than the correlation time.

The spectra and decay times of the 4.3- and 3.7-eV luminescence bands associated with the self-trapped excitons (STE’s) in CsI have been observed in a wide temperature range (4.5–300 K) by using two-photon spectroscopy. The results reveal that the 4.1-eV luminescence in pure CsI, which is well known as the room-temperature scintillation, appears mainly from the 4.3-eV STE state: the 4.3-eV STE luminescence is dominant below 6 K and is quenched above 6 K, but appears again at 4.1 eV at room temperature by thermal activation of STE’s from the 3.7-eV STE state to the 4.3-eV STE state.

Using junction-capacitance methods, we study the thermal charge emission of holes trapped in the dangling-bond defect D of p-type a-Si:H. Over a significant temperature range, we find a linear temperature-independent relation between emission time and the residence time of the hole on the D defect. We attribute this characteristic to a structural-relaxation process that is slow in disordered materials.

Two-color picosecond pump-probe measurements in semiconductor nanocrystallite doped glasses reveal nonexponential decay of photoexcited carriers. The dependence of the decay on nanocrystallite size, pump intensity, temperature, and probe wavelength are examined and discussed within the framework of continuous-time random-walk models for transport of carriers among localized trap sites. This analysis suggests that carrier transport in lower dimensions is involved in the relaxation of these nano- scale systems.

Thermal conductivity and thermal diffusivity of a two-layer system are examined from the theoretical point of view. We use the one-dimensional heat-diffusion equation with the appropriate solution in each layer and boundary conditions at the interfaces to calculate the heat transport in this bounded system. We also consider the heat flux at the surface of the sample as a boundary condition instead of using a fixed temperature. From this, we obtain an expression for the effective thermal diffusivity of the composite sample in terms of the thermal diffusivity of its constituent materials without any approximations.

The thermoelectric power of charge carriers heated under a strong applied electric field in semiconductors is obtained by use of the nonequilibrium-statistical-operator (NSO) method. The balance equations are derived in terms of the NSO density matrix and the force-force correlation functions which can easily be calculated for a system with electron-impurity and electron-phonon interactions. A numerical study has been performed for hole-doped Ge. It is shown that the hot-electron thermoelectric power is sensitively affected by the applied electric field and that its sign is reversed at higher electric fields.

We have measured the frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz to 100 kHz at different temperatures. The conductivity data exhibit a strong frequency dependence. When normalized to the dc conductivity, our data obey a universal scaling law, with a well-defined crossover in which the real part of the conductivity σ’ changes from an ${\mathrm{\omega }}^{1/2}$ dependence to being proportional to ω. We explain this in terms of activated hopping in a fractal network. The low-frequency regime is governed by the fractal properties of porous Si, whereas the high-frequency dispersion comes from a broad distribution of activation energies. Calculations using the effective-medium approximation for activated hopping on a percolating lattice give fair agreement with the data.

We present low-temperature resistivity measurements, carried out in the temperature range 100–400 mK on uncompensated Si:P samples doped by ion implantation in the just-metallic side of the metal-insulator transition. As the dopant concentration increases the experimental data confirm the presence of the change of sign in the √T -dependent correction to the conductivity, with a cusplike behavior of the critical prefactor. However, the sign transition is followed by the turning on of an anomalous temperature contribution. We analyze both features in terms of renormalization of electron-electron interaction effects and show that in Si:P the effective-electron-coupling constant has a sizable enhancement both with doping and temperature.

Relative total energies for structures produced by adsorption of arsine on Si(100) are calculated using the local-density approximation and first-principles pseudopotential method. Bridge-bonded As monomers and As-H structures are proposed as possible metastable configurations that could form under deposition conditions in which As migration is suppressed. However, these structures are found to be unstable with respect to the formation of rows containing one or more As-As dimers, with the H atoms capping off the remaining Si dangling bonds. These results are consistent with scanning-tunneling-microscopy images as well as measurements of the saturation As coverage by x-ray photoemission spectroscopy. An attractive pairing energy for hydrogen on Si dimers is calculated and found to be 0.25 eV.

We investigate the problem of an electron gas interacting with longitudinal-optical phonons in a two-dimensional polar-semiconductor quantum well for the entire range of the coupling parameter using the Feynman path-integral method and the random-phase approximation. We show that at a critical value of the electron concentration an optical polaron will undergo a transition from the localized state to a mobile state.

The light-emission mechanism of Si-MOS (metal-oxide-semiconductor) junctions has been investigated. Si/${\mathrm{SiO}}_2$/metal (Al or Au) MOS junctions with extremely smooth interfaces were fabricated by taking advantage of the well-developed Si processing technology. The observed light-emission spectra can be accounted for by the current fluctuation theory of light-emitting tunnel junctions [B. Laks and D. L. Mills, Phys. Rev. B 20, 4962 (1979)]. There are two channels of light emission: the direct emission from the fluctuation of the tunneling current and the indirect emission that arises from the scattering (by surface roughness) of surface-plasmon polaritons generated by the fluctuating tunnel current. The light from the Si/${\mathrm{SiO}}_2$/Al junction arises mainly from the direct emission from the fluctuating current. The light from the Si/${\mathrm{SiO}}_2$/Au junction contains both the direct and indirect emissions with approximately equal strengths. The direct and indirect emissions have comparable strength in our junctions, because our Si-based junctions are extremely smooth and the indirect emission is much weaker than in the junctions used in earlier studies.

In this work x-ray-diffraction measurements from GaAs surface gratings are presented. The experiments were performed using a three-crystal diffractometer. Measurements in the region of total external reflection (small incidence angles) for five samples were done and compared with model calculations based on a dynamical scattering theory. The theory is able to explain all experiments quantitatively. Mesoscopic grating parameters as well as microscopic surface roughnesses of the samples were obtained from fits of the data. For three samples scanning-electron-microscope pictures were taken. The analysis of these pictures leads to the same mesoscopic parameters as obtained from x-ray diffraction.

We present Raman-scattering and photoluminescence measurements on a laterally drifting two-dimensional electron gas (2DEG) formed at a GaAs-${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As heterojunction. The backscattering geometry employed allows both the direction, parallel, antiparallel, or perpendicular to the drift direction, and magnitude of the in-plane scattering wave vector to be varied. For a fixed wave vector the drift current produces a Doppler shift and broadening of the intrasubband plasmon Raman peak. For small drift velocities the energy shift is linear, and in opposite directions for the Stokes and anti-Stokes spectra, but becomes nonlinear for large drift velocities, and in the same direction in both cases. This change in behavior is ascribed to increasing carrier density with drift. Single-particle relaxation times were determined from the broadening of the plasmon Raman peaks. The ratio of the intensities of the Stokes and anti-Stokes plasmon peaks provides an estimate of the 2DEG temperature under drift conditions; this increased considerably with drift current, as confirmed by the high-energy tail of the band-gap photoluminescence from the 2DEG.

The effects of both electric and magnetic fields on the transition energies between the 1s-like ground state and 2${\mathit{p}}_{\pm }$ excited states of hydrogenic donors in a GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum well are studied. The effective-mass approximation within a variational scheme is adopted with electric and magnetic fields considered in the growth direction of the heterostructure, and treated directly in the variational calculation. Results for the finite-barrier potential are obtained as functions of both applied fields and for different GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum-well thicknesses, and compared with available infrared magnetospectroscopy measurements on donor-doped quantum wells. Theoretical results indicate that a detailed study of the intradonor absorption spectra together with a proper consideration of the impurity-doping profile are necessary for a qualitative understanding of the experimental results.

Locally epitaxial diamond films on mirror-polished Si(001) substrates have been prepared by using surface-biasing pretreatment in a hot-filament chemical-vapor-deposition system in our laboratory. The diamond is in epitaxial alignment with the silicon substrate, with approximately diamond (001) parallel to Si(001) and the [110] directions of the epitaxial layer parallel to the silicon surface. High-resolution cross-sectional electron microscopy clearly shows that there are about 40 rows of carbon-atom planes on 25 rows of silicon-atom planes in the observed epitaxial interface. The dislocation density is very high in the interface, but the diamond (1¯11¯) planes are shown to be continuous across the interface with 7.3° towards [001]. The three components of dislocations that are formed at the interface are discussed. The interfacial tilting and azimuthal rotational misorientation are shown to come from these dislocations. The relationship between the tilting angles and high-misfit-dislocation density is analyzed.

The magnetoelectric spectrum of a two-dimensional electron gas partially constrained to a channel by adjustable split-gate potentials and subject to a normal magnetic field confined to the channel region is solved analytically for a particular choice of the electromagnetic fields. Several physical results are discussed, particularly a transistor effect that results from the asymmetry of the Hall conductance.

Evaluating the full expression for the tunneling current density in a resonant-tunneling diode generally involves the numerical computation of a triple integral. Since this presents such a formidable task, quite often one neglects any explicit dependence of the transmission coefficient on the wave vector in the plane of the interfaces, ${\mathbf{k}}_{\mathrm{\parallel }}$, resulting in a single-integral expression. This one-dimensional approximation has been widely used in the literature. We demonstrate that this approximation, even when applied to rather ordinary devices, can lead to unphysical current-density bias graphs and explain the reasons behind the failure.

We have studied three types of broadening effects in quantum point contacts: temperature smearing, broadening due to high source-drain voltages, and broadening due to Joule heating. We are able to calculate the relative strength of the three mechanisms by using the parabolic-saddle-potential approximation. The voltage smearing effect can in most cases be disregarded in comparison with the thermal effects. The Joule heat produced in the constriction by the current is carried away by a thermal conductance intermediate between the low conductance of the quantum point contact and the high conductance of the surrounding two-dimensional electron gas, indicating which part of the dissipation results from the one-dimensional modes in the constriction.