Effect of inter-miniband tunneling on current resonances due to the formation of stochastic conduction networks in superlattices

We study the effects of inter-miniband electron tunneling and electric field domains on the current–voltage and conductance–voltage curves of biased semiconductor superlattices under the action of a magnetic field that is tilted relative to the plane of the layers. For this geometry, electrons in the superlattice minibands exhibit a unique type of stochastic semiclassical motion. At certain critical values of the electric field within the superlattice layers, the stochastic trajectories change abruptly from fully localized to completely unbounded, and map out an intricate web-like mesh of conduction channels in phase space. Delocalization of the electron paths produces a series of strong resonant peaks in the electron drift velocity versus electric field curves. We use these drift velocity characteristics to make self-consistent drift-diffusion calculations of the current–voltage and differential conductance–voltage curves of the superlattices, which reveal strong resonant features originating from the sudden delocalization of the stochastic single-electron paths. We show that this delocalization has a pronounced effect on the distribution of space charge and electric field domains within the superlattices. Inter-miniband tunneling greatly reduces the amount of space-charge buildup, thus enhancing the domain structure and both the strength and number of the current resonances.     

Stress in dielectric contact layers on metals

Several sources of stress in dielectric contact layers (e.g. growing oxide films) are discussed and order-of-magnitude estimates are given for the accompanying strains. The strain distributions in isotropic layers are deduced for stresses produced by Coulomb forces, volume changes associated with diffusing defects, orienting molecular force (epitaxial) effects, and electrochemical potential gradients producing diffusion currents and growth of the layer.     

Parabolic oxidation of metals in homogeneous electric fields

A previously proposed thin film parabolic growth law (Fromhold, 1963) is extended to include film growth due to any number of diffusing defect species of arbitrary valence, and an analysis is made of the effects of applying external electrostatic potentials during oxidation. The total electrical conductivity and the partial conductivities are markedly position-dependent in the protective film, varying by orders of magnitude from one interface to the other. The built in electrostatic potential across the film is independent of thickness of the film and is a function of the partial conductivities of the diffusing ionic and electronic defect species. Effects of electrical shorting of the oxide film by external circuitry are analyzed. Depending on polarity, a constant applied potential can increase or decrease the rate constant but does not alter the kinetics from the parabolic form, in accordance with published experimental data. The net electrostatic potential required to stop metal oxidation is derived for the model in question. For growth by a single ionic species, the stopping potential is that electrostatic potential which gives an equal electrochemical potential at the metal-oxide and the oxideoxygen interfaces. For growth by multiple ionic species, the stopping potential is a function of the ionic partial conductivities.     

A physical explanation for the origin of self-similar magnetoconductance fluctuations in semiconductor billiards

We report quantum-mechanical calculations which replicate the self-similar magnetoconductance fluctuations observed in recent experiments on semiconductor Sinai billiards. We interpret these fluctuations by considering the mixed stable-chaotic classical dynamics of electrons in the billiard. In particular, we show that the fluctuation patterns are dominated by individual stable orbits. The scaling characteristics of the self-similar fluctuations depend on the geometry of the associated stable orbit. We find that our analysis is insensitive to the details of the potential landscape, and is applicable to real devices with a wide range of soft-wall profiles. We show that our analysis also provides a possible explanation for the distinct series of magnetoconductance fluctuations observed in recent experiments on carbon nanotubes.     

The effect of temperature on the nonlinear dynamics of charge in a semiconductor superlattice in the presence of a magnetic field

The space-time dynamics of electron domains in a semiconductor superlattice is studied in a tilted magnetic field with regard to the effect of temperature. It is shown that an increase in temperature substantially changes the space-time dynamics of the system. This leads to a decrease in the frequency and amplitude of oscillations of a current flowing through the semiconductor superlattice. The quenching of oscillations is observed, which is attributed to the change in the drift velocity as a function of electric-field strength under the variation of temperature.     

Chaotic ray dynamics in slowly varying two-dimensional photonic crystals

We use Hamiltonian optics to investigate chaotic ray dynamics in a photonic crystal whose lattice parameters vary slowly with position. The ray dynamics are chaotic even in regimes where only stable motion has been found in previous studies of energy band transport. Stable ray paths provide dynamical barriers that localize chaotic motion to certain regions of the photonic crystal.