Effect of temperature on resonant electron transport through stochastic conduction channels in superlattices (original) (raw)
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Physical Review B, 2019
We address the increase of electron drift velocity that arises in semiconductor superlattices (SLs) subjected to constant electric and magnetic fields. It occurs if the magnetic field possesses nonzero components both along and perpendicular to the SL axis and the Bloch oscillations along the SL axis become resonant with cyclotron rotation in the transverse plane. It is a phenomenon of considerable interest, so that it is important to understand the underlying mechanism. In an earlier Letter (Phys. Rev. Lett. 114, 166802 (2015)) we showed that, contrary to a general belief that drift enhancement occurs through chaotic diffusion along a stochastic web (SW) within semiclassical collisionless dynamics, the phenomenon actually arises through a non-chaotic mechanism. In fact, any chaos that occurs tends to reduce the drift. We now provide fuller details, elucidating the mechanism in physical terms, and extending the investigation. In particular, we: (i) demonstrate that pronounced drift enhancement can still occur even in the complete absence of an SW; (ii) show that, where an SW does exist and its characteristic slow dynamics comes into play, it suppresses the drift enhancement even before strong chaos is manifested; (iii) generalize our theory for non-small temperature, showing that heating does not affect the enhancement mechanism and accounting for some earlier numerical observations; (iv) demonstrate that certain analytic results reported previously are incorrect; (v) provide an extended critical review of the subject and closely related issues; and (vi) discuss some challenging problems for the future.
Theory of charge fluctuations and domain relocation times in semiconductor superlattices
Physica D: Nonlinear Phenomena
Shot noise affects differently the nonlinear electron transport in semiconductor superlattices depending on the strength of the coupling among the superlattice quantum wells. Strongly coupled superlattices can be described by a miniband Boltzmann-Langevin equation from which a stochastic drift-diffusion equation is derived by means of a consistent Chapman-Enskog method. Similarly, shot noise in weakly coupled, highly doped semiconductor superlattices is described by a stochastic discrete drift-diffusion model. The current-voltage characteristics of the corresponding deterministic model consist of a number of stable branches corresponding to electric field profiles displaying two domains separated by a domain wall. If the initial state corresponds to a voltage on the middle of a stable branch and is suddenly switched to a final voltage corresponding to the next branch, the domains relocate after a certain delay time, called relocation time. The possible scalings of this mean relocation time are discussed using bifurcation theory and the classical results for escape of a Brownian particle from a potential well.
Physical Review E, 2017
When quantized, traces of classically chaotic single particle systems include eigenvalue statistics and scars in eigenfuntions. Since 2001, many theoretical and experimental works have argued that classically chaotic single electron dynamics influences and controls collective electron transport. For transport in semiconductor superlattices under tilted magnetic and electric fields, these theories rely on a reduction to a one-dimensional self-consistent drift model. A two-dimensional theory based on self-consistent Boltzmann transport does not support that single electron chaos influences collective transport. This theory agrees with existing experimental evidence of current self-oscillations, predicts spontaneous collective chaos via a period doubling scenario and it could be tested unambiguously by measuring the electric potential inside the superlattice under a tilted magnetic field.
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.
Journal of Physics: Condensed Matter, 2002
Nonlinear charge transport in semiconductor superlattices under strong electric fields parallel to the growth direction results in rich dynamical behaviour including the formation of electric field domains, pinning or propagation of domain walls, self-sustained oscillations of the current and chaos. Theories of these effects use reduced descriptions of transport in terms of average charge densities, electric fields, etc. This is simpler when the main transport mechanism is resonant tunnelling of electrons between adjacent wells followed by fast scattering between subbands. In this case, we will derive microscopically appropriate discrete models and boundary conditions. Their analyses reveal differences between low-field behaviour where domain walls may move oppositely or parallel to electrons, and high-field behaviour where they can only follow the electron flow. The dynamics is controlled by the amount of charge available in the superlattice and doping at the injecting contact. When the charge inside the wells becomes large, boundaries between electric field domains are pinned resulting in multistable stationary solutions. Lower charge inside the wells results in self-sustained oscillations of the current due to recycling and motion of domain walls, which are formed by charge monopoles (high contact doping) or dipoles (low contact doping). Besides explaining wave motion and subsequent current oscillations, we will show how the latter depend on such controlling parameters as voltage, doping, temperature, and photoexcitation.
Non-Linear Charge Dynamics in Semiconductor Superlattices
2000
In the last decade, non-linear dynamical transport in semiconductor superlattices (SLs) has witnessed significant progress in theoretical descriptions as well as in experimentally observed non-linear phenomena. However, until now, a clear distinction between non-linear transport in strongly and weakly coupled SLs was missing, although it is necessary to provide a detailed description of the observed phenomena. In this review, strongly coupled SLs are described by spatially continuous equations and display self-sustained current oscillations due to the periodic motion of a charge dipole as in the Gunn effect for bulk semiconductors. In contrast, weakly coupled SLs have to be described by spatially discrete equations. Therefore, weakly coupled SLs exhibit a more complex dynamical behaviour than strongly coupled ones, which includes the formation of stationary electric field domains, pinning or propagation of domain walls consisting of a charge monopole, switching between stationary domains, self-sustained current oscillations due to the recycling motion of a charge monopole and chaos. This review summarizes the existing theories and the experimentally observed non-linear phenomena for both types of semiconductor SLs.
Dynamics of electronic transport in a semiconductor superlattice with a shunting side layer
Physical Review B, 2009
We study a model describing electronic transport in a weakly-coupled semiconductor superlattice with a shunting side layer. Key parameters include the lateral size of the superlattice, the connectivity between the quantum wells of the superlattice and the shunt layer, and the conduction properties of the shunt layer. For a superlattice with small lateral extent and high quality shunt, static electric field domains are suppressed and a spatially-uniform field configuration is predicted to be stable, a result that may be useful for proposed devices such as a superlattice-based TeraHertz (THz) oscillators. As the lateral size of the superlattice increases, the uniform field configuration loses its stability to either static or dynamic field domains, regardless of shunt properties. A lower quality shunt generally leads to regular and chaotic current oscillations and complex spatio-temporal dynamics in the field profile. Bifurcations separating static and dynamic behaviors are characterized and found to be dependent on the shunt properties.
Stochastic webs and quantum transport in superlattices: an introductory review
Contemporary Physics, 2010
Stochastic webs were discovered, first by Arnold for multi-dimensional Hamiltonian systems, and later by Chernikov et al. for the low-dimensional case. Generated by weak perturbations, they consist of thread-like regions of chaotic dynamics in phase space. Their importance is that, in principle, they enable transport from small energies to high energies. In this introductory review, we concentrate on low-dimensional stochastic webs and on their applications to quantum transport in semiconductor superlattices subject to electric and magnetic fields. We also describe a recently-suggested modification of the stochastic web to enhance chaotic transport through it and we discuss its possible applications to superlattices.
Nonlinear Electron and Spin Transport in Semiconductor Superlattices
SIAM Journal on Applied Mathematics, 2008
Nonlinear charge transport in strongly coupled semiconductor superlattices is described by Wigner-Poisson kinetic equations involving one or two minibands. Electron-electron collisions are treated within the Hartree approximation whereas other inelastic collisions are described by a modified BGK (Bhatnaghar-Gross-Krook) model. The hyperbolic limit is such that the collision frequencies are of the same order as the Bloch frequencies due to the electric field and the corresponding terms in the kinetic equation are dominant. In this limit, spatially nonlocal drift-diffusion balance equations for the miniband populations and the electric field are derived by means of the Chapman-Enskog perturbation technique. For a lateral superlattice with spin-orbit interaction, electrons with spin up or down have different energies and their corresponding drift-diffusion equations can be used to calculate spin-polarized currents and electron spin polarization. Numerical solutions show stable self-sustained oscillations of the current and the spin polarization through a voltage biased lateral superlattice thereby providing an example of superlattice spin oscillator. PACS numbers:
Non-linear dynamics of semiconductor superlattices
Reports on Progress in Physics, 2005
In the last decade, non-linear dynamical transport in semiconductor superlattices has witnessed a significant progress in the theoretical description as well as in the experimentally observed non-linear phenomena. However, until now, a clear distinction between non-linear transport in strongly and weakly coupled superlattices was missing, although it is necessary for a detailed description of the observed phenomena. In this review, strongly coupled superlattices are described by spatially continuous equations and display self-sustained current oscillations due to the periodic motion of a charge dipole as in the Gunn effect for bulk semiconductors. In contrast, weakly coupled superlattices have to be described by spatially discrete equations. Therefore, weakly coupled superlattices exhibit a more complex dynamical behaviour than strongly coupled ones, which includes the formation of stationary electric field domains, pinning or propagation of domain walls consisting of a charge monopole, switching between stationary domains, self-sustained current oscillations due to the recycling motion of a charge monopole, and chaos. This review summarizes the existing theories and the experimentally observed non-linear phenomena for both types of semiconductor superlattices. ยง To whom correspondence should be addressed (bonilla@ing.uc3m.es)