Stochastic webs and quantum transport in superlattices: an introductory review (original) (raw)
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Transport in random quantum dot superlattices
Journal of Applied Physics, 2002
We present a novel model to calculate single-electron states in random quantum dot superlattices made of wide-gap semiconductors. The source of disorder comes from the random arrangement of the quantum dots (configurational disorder) as well as spatial inhomogeneities of their shape (morphological disorder). Both types of disorder break translational symmetry and prevent the formation of minibands, as occurs in regimented arrays of quantum dots. The model correctly describes channel mixing and broadening of allowed energy bands due to elastic scattering by disorder.
Hopping transport in superlattices
Superlattices and Microstructures, 1997
We calculate the d.c.-current of a semiconductor superlattice in the hopping conduction picture. Electronic transport in this regime is described by hopping transitions between the partially localized Wannier–Stark states. In our numerical model we start from the exact wavefunctions of the superlattice and include both impurity and acoustic phonon scattering. We then obtain the electron drift velocity by considering the
Physical Review B, 2011
We show that resonant electron transport in semiconductor superlattices with an applied electric and tilted magnetic field can, surprisingly, become more pronounced as the lattice and conduction electron temperature increases from 4.2 K to room temperature and beyond. It has previously been demonstrated that at certain critical field parameters, the semiclassical trajectories of electrons in the lowest miniband of the superlattice change abruptly from fully localized to completely unbounded. The unbounded electron orbits propagate through intricate web patterns, known as stochastic webs, in phase space, which act as conduction channels for the electrons and produce a series of resonant peaks in the electron drift velocity versus electric-field curves. Here, we show that increasing the lattice temperature strengthens these resonant peaks due to a subtle interplay between the thermal population of the conduction channels and transport along them. This enhances both the electron drift velocity and the influence of the stochastic webs on the current-voltage characteristics, which we calculate by making self-consistent solutions of the coupled electron transport and Poisson equations throughout the superlattice. These solutions reveal that increasing the temperature also transforms the collective electron dynamics by changing both the threshold voltage required for the onset of self-sustained current oscillations, produced by propagating charge domains, and the oscillation frequency.
Physica B: Condensed Matter, 1998
We present a theoretical analysis of the correlations between the macroscopic global transport properties and microscopic imperfections of a superlattice. High-field transport and domain formation is modelled using a microscopic quantum transport model which includes interface roughness and impurity scattering and describes resonant and nonresonant tunnelling processes in weakly coupled multiple quantum wells without adjustable parameters. Our analysis can be used on one hand to identify random fluctuations of the structural parameters in real samples like deviations from the perfect periodicity due to varying barrier widths, or doping densities in the individual wells. On the other hand, we demonstrate that the current-voltage characteristics can be tailored in a wide range to exhibit specific features like sharply rising steps at given voltages, arbitrarily modulated current maxima of multistable branches, or self-generated current oscillations.
Transport spectroscopy of quantum wires and superlattices
Thin Solid Films, 2000
A new device based on side-gated wires demonstrates that the side gate wire technique can be successfully implemented as a novel selective depletion scheme for vertical tunneling devices. Resonant tunneling between 1D states was achieved by an additional lateral con®nement generated by a central gate. From model considerations assuming a parabolic con®nement, the tuning range of the subband energy was estimated to lie between 0 meV and 5±6 meV. The transmittance of strongly coupled superlattices at different superlattice bias conditions is measured by varying the energy of the injected hot electron beam. The onset of scattering-induced miniband transport is clearly evident and the transition between coherent and incoherent electron transport in superlattices is observed for the ®rst time. A coherence length of 150 nm and a scattering time of 1 ps is determined. The experimental result is in good agreement to a fully three-dimensional calculation including interface roughness with typical island sizes of 10 nm. This clearly demonstrates that interface roughness scattering limits the coherence length of ballistic electrons in the superlattice.
Chaotic transport in low-dimensional superlattices
Physical Review B, 2003
We predict that in arrays of quantum dots 0D superlattice and arrays of one-dimensional quantum wires 1D superlattice chaotic transport should be observed in the presence of an ac field and for a wide range of physical parameters, like the external dc bias, contact charge, doping levels, and disorder in the array. Timedependent current oscillations set in the array due to the formation of electric domain walls when sequential resonant tunneling is the main transport mechanism between adjacent units. Such oscillations can then be ...
Influence of miniband widths and interface disorder on vertical transport in superlattices
1993
The nature of transport through superlattice minibands is addressed in this paper. All-optical techniques have been used to study the vertical transport, monitoring the luminescence from an enlarged well grown within the superlattice. Photoluminescence, photoluminescence excitation spectroscopy, and time-resolved luminescence-decay measurements have been performed as a function of temperature and excitation intensity. A consistent picture emerges from the experimental data, showing the key role played by the superlattice miniband widths and interface disorder on the vertical transport at low temperatures (4-40 K).
Quantum transport in weakly coupled superlattices at low temperature
Physical Review B, 2010
We report on the study of the electrical current flowing through weakly coupled superlattice (SL) structures under an applied electric field and at very low temperature, i.e. in the tunneling regime. This low temperature transport is characterized by an extremely low tunneling probability between adjacent wells. Experimentally, I(V) curves at low temperature display a striking feature, i.e a plateau or null differential conductance. A theoretical model based on the evaluation of the scattering rates is developed in order to understand this behavior, exploring the different scattering mechanisms in AlGaAs alloys. The dominant interaction in our typical operating conditions is found to be the electron-ionized donors scattering. The existence of the plateau in the I(V) characteristics is physically explained by a competition between the electric field localization of the Wannier-Stark electron states in the weakly coupled quantum wells and the electric field assisted tunneling between adjacent wells. The influence of the doping concentration and profile as well as the presence of impurities inside the barrier are discussed. PACS number(s): 73.63.Hs, 72.10.-d, 85.60.Gz I. * * dzdz e
Nonlinear Transport in Semiconductor Superlattices
Mathematics in Industry, 2002
Nonlinear electronic transport in weakly coupled superlattices results in formation of electric field domains, self-sustained current oscillations (periodic, quasiperiodic or chaotic), wave propagation and other interesting phenomena. These are explained here by means of a discrete self-consistent model including quantum mechanically calculated tunneling current, detailed electrostatics and appropiate boundary conditions. Simpler discrete drift-diffusion models (for which analytical results are known) are also derived from our model.