I. Gómez

TRANSPORT THROUGH A QUANTUM WIRE WITH A SIDE QUANTUM-DOT ARRAY

A noninteracting quantum-dot array side coupled to a quantum wire is studied. Transport through the quantum wire is investigated by using a noninteracting Anderson tunneling Hamiltonian. The conductance at zero temperature develops an oscillating band with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. Moreover, we have found an odd-even parity in the system, whose conductance vanishes for an odd number of quantum dots while it becomes 2e(2)/h for an even number. We established an explicit relation between this odd-even parity and the positions of the resonances and antiresonances of the conductivity with the spectrum of the isolated quantum-dot array.

Electron transport across a Gaussian superlattice

We study the electron transmission probability in semiconductor superlattices where the height of the barriers is modulated by a Gaussian profile. Such structures act as efficient energy band-pass filters and, contrary to previous designs, it is expected to present a lower number of unintentional defects and, consequently, better performance. The j–V characteristic presents negative differential resistance with peak-to-valley ratios much greater than in conventional semiconductor superlattices.

Transport in random quantum dot superlattices

We present a model based on the two-dimensional transfer matrix formalism to calculate single-electron states in a random wide-gap semiconductor quantum dot superlattice. With a simple disorder model both the random arrangement of quantum dots (configurational disorder) and the spatial inhomogeneities of their shape (morphological disorder) are considered. The model correctly describes channel mixing and broadening of allowed energy bands due to elastic electron scattering by disorder.

Electron States in a Class of One-Dimensional Random Binary Alloys

We present a model for alloys of compound semiconductors by introducing a one-dimensional binary random system where impurities are placed in one sublattice while host atoms lie on the other sublattice. The source of disorder is the stochastic fluctuation of the impurity energy from site to site. Although the system is one-dimensional and random, we demonstrate analytically and numerically the existence of a set of extended states in finite systems, whose energy lies close to that of host atoms.

Nature of the extended states in random dimer-barrier superlattices

We theoretically study electron transmission in intentionally disordered GaAs–AlxGa1� xAs superlattices with structural short-range correlations in the Al mole fraction of the AlxGa1� xAs layers. The Al mole fraction in the equalwidth AlxGa1� xAs layers takes at random two different values, but with the constraint that one of them only appears at random in pairs, while GaAs layers are identical. We demonstrate that the superlattice supports two types of extended states, one of them comes from resonance effects at dimer barriers, as it was already reported for random dimer well superlattices, while the other type arises as a consequence of the binary nature of this heterostructure. Conditions for their observation in transport experiments are discussed. r 2002 Elsevier Science B.V. All rights reserved.

Electron scattering on disordered double-barrier GaAs–AlxGa1−xAs heterostructures

Abstract We present a novel model to calculate vertical transport properties such as conductance and current in unintentionally disordered double-barrier GaAs–Al x Ga 1− x As heterostructures. The source of disorder comes from interface roughness at the heterojunctions (lateral disorder) as well as spatial inhomogeneities of the Al mole fraction in the barriers (compositional disorder). Both lateral and compositional disorder break translational symmetry along the lateral direction and therefore electrons can be scattered off the growth direction. The model correctly describes channel mixing due to these elastic scattering events. In particular, for realistic degree of disorder, we have found that the effects of compositional disorder on transport properties are negligible as compared to the effects due to lateral disorder.

Gaussian semiconductor superlattices

We study GaAs-AlxGa1−xAs superlattices where the heights of the barriers are modulated by a Gaussian profile. Such structures present bands of almost unscattered electronic states. The calculated energy levels of the superlattice agree well with the photoluminescence spectra recorded at low temperature.

X-ray filter using multilayers with modulated refractive index

Abstract We have numerically computed the reflectivity of X-rays incident normally onto metallic multilayers. The structure consists of two alternating types of constituent layers. One type has the same refractive index whereas the refractive index of the other type is modulated by a Gaussian function along the normal direction. We have found that the reflectivity of the structure becomes unity in a wide range of wavelengths. The bandwidth of the reflection can be finely tuned by varying the width of the Gaussian function.

Complex behavior of the conductance of quantum wires with a long quantum-dot array

We consider electron transport through a quantum wire with an attached quantum-dot array, when the number of dots is large. To this end, we use a noninteracting Anderson Hamiltonian. The conductance at zero temperature shows a complex behavior as a function of the Fermi energy. In particular, two well-defined energy regions are observed. Far from the site-energy of the quantum dots, the conductance depends smoothly on the Fermi energy. On the contrary, at the center of the band the conductance develops an oscillating pattern with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. We discuss analytically in detail the physical origin of this complex behavior.

Fano-like resonances in three-quantum-dot Aharonov–Bohm rings

In this work we study electron transport through quantum wires coupled to a quantum dot Aharonov–Bohm ring by using a noninteracting Anderson tunnelling Hamiltonian. In the case of an asymmetric coupling and three dots within the Aharonov–Bohm ring we have observed the appearance of Fano-like resonances in the conductance. We have investigated the asymmetry and the position of the conductance resonances and found closed expressions. We have also observed Aharonov–Bohm oscillations. Finally the local density of states as well as the probability amplitude phases have been studied.