Modulated Bloch Waves in Semiconductor Superlattices (original) (raw)

Theory of spatially inhomogeneous Bloch oscillations in semiconductor superlattices

Physical Review B, 2011

In a semiconductor superlattice with long scattering times, damping of Bloch oscillations due to scattering is so small that nonlinearities may compensate it and Bloch oscillations persist even in the hydrodynamic regime. To demonstrate this, a Boltzmann-Poisson transport model of miniband superlattices with inelastic collisions is proposed and hydrodynamic equations for electron density, electric field and the complex amplitude of the Bloch oscillations are derived by singular perturbation methods. For appropriate parameter ranges, numerical solutions of these equations show stable Bloch oscillations with spatially inhomogeneous field, charge, current density and energy density profiles. These Bloch oscillations disappear as scattering times become sufficiently short.

Spatially confined Bloch oscillations in semiconductor superlattices

EPL (Europhysics Letters), 2011

In a semiconductor superlattice with long scattering times, damping of Bloch oscillations due to scattering is so small that convective nonlinearities may compensate it and Bloch oscillations persist even in the hydrodynamic regime. In this case, numerical solutions show that there are stable Bloch oscillations confined to a region near the collector with inhomogeneous field, charge, current density and energy density profiles. These Bloch oscillations disappear when damping due to inelastic collisions becomes sufficiently strong.

Nonlinear Electronic Transport in Semiconductor Superlattices

Applied and Industrial Mathematics in Italy Ii, 2007

We propose novel BGK models for inelastic collisions in the kinetic theory of electron transport in semiconductor superlattices. The Chapman-Enskog method produces a drift-diffusion equation describing the behavior of the electric field F and the electron density n in an appropriate hyperbolic limit. Under voltage bias, stable solutions thereof include stable self-sustained oscillations of the current through the superlattice due to periodic injection of electric field pulses at one end of the device that move to the other end. For almost elastic collisions, the model has a local equilibrium that oscillates rapidly in time and the resulting balance equations describe for the first time the annihilation of the Bloch oscillations due to scattering.

Bloch oscillations in superlattices: Monte-Carlo analysis using 2D scattering model

Physica E-low-dimensional Systems & Nanostructures, 2003

We studied the behavior of Bloch oscillations (BO) in AlGaAs/GaAs superlattices by Monte-Carlo method. Two different scattering models based on effective mass approximation were used for studying of electron miniband transport. Scattering on polar optical and acoustic phonons as well as impurities were taken into account. Behavior of BO was studied under different conditions such as the intensity of electric field, temperature and ionized impurity density.

Bloch Oscillations of Excitonic Wave-Packets in Semiconductor Superlattices

Physical Review B, 1994

Vfe present a detailed investigation of the coherent dynamics of excitonic wave packets composed of heavy/light-hole, electron miniband, and Wannier-Stark states in GaAs/Al Gai As superlattices. Using transient degenerate four-wave mixing, we study the dependence of Bloch oscillations and heavy/light-hole beats on the applied field, miniband width, lattice temperature, and excitation conditions. Bloch oscillations are observed in samples with minibandwidths varying from 13 to 46 meV and at lattice temperatures up to 200 K. Under certain excitation conditions, we observe higher harmonics of the Bloch oscillation frequency. Spectrally resolved transient four-wave mixing experiments show unambiguously that quantum-mechanical interference is the origin of the oscillations. The experimental four-wave mixing traces are compared with a theoretical model based on many-level third-order density-matrix theory.

Miniband transport and oscillations in semiconductor superlattices

Nanotechnology, 2004

We present and analyse solutions of a recent derivation of a drift-diffusion model of miniband transport in strongly coupled superlattices. The model is obtained from a single-miniband Boltzmann-Poisson transport equation with a BGK (Bhatnagar-Gross-Krook) collision term by means of a consistent Chapman-Enskog expansion. The reduced drift-diffusion equation is solved numerically and travelling field domains and current oscillations are obtained. A broad range of frequencies can be achieved, depending on the model parameters, in good agreement with available experiments on GaAs/AlAs superlattices.

Time-resolved optical investigations of bloch oscillations in semiconductor superlattices

Solid-State Electronics, 1996

We present a complementary study of the interband and intraband dynamics of optically excited Bloch oscillations in GaAs/AI,Ga, _ ,As superlattices. Distinct differences in the frequency and dephasing of the oscillations give evidence for Bloch oscillations performed by electrons in continuum states and by excitonic wavepackets. The dephasing time of the electronic continuum states is found to be exceptionally long as compared to the excitonic dephasing time under identical excitation conditions. These observations are confirmed by THz emission experiments, where Bloch oscillations are detected under optical excitation well above the fundamental band gap. The experimental observations suggest that the electronic coherence may be partially maintained during relaxation and momentum scattering processes.

Coupling of electromagnetic waves and Bloch oscillations in quantum superlattice

2003 Third IEEE Conference on Nanotechnology, 2003. IEEE-NANO 2003.

In this report we analyze, for the first time to our knowledge, the linear coupling of the Bloch oscillations and transversal electromagnetic waves in a quantum semiconductor superlattice (QSSL) towards the problem of realization of the tunable THz source. The analysis is implemented by means of wave equation for the electromagnetic field and the material equations with quasi-classic description of the electron transport in a biased QSSL. In the case when the Bloch frequency is greater than plasma frequency at the bottom of the lowest miniband of QSSL, the coupling leads to the reconnection of the dispersion curves at the region of their crossing, forming a slit between always stable high-frequency branch and lower frequency branch which has the region of an instability due to electron bunching in the momentum space. The last circumstance opens the great possibility to generate THz radiation in QSSL superimposed with an inhomogeneous dc field that is provided by the presence of the turning points for the electromagnetic waves. Such turning points play the role of the mirrors making up a resonator for the unstable waves. For the typical GaAslGaAlAs QSSL with miniband electron density IO"cmJ and superlattice period 5nm the critical strength of applied de electric field which leads to spectrum splitting is about 9kV/cm.

Bloch oscillations in superlattice simulated by the Monte Carlo method

1997

The Monte Carlo based semiclassical model for the vertical electron transport in superlattice including most important features of electron transport through the superlattice minibands is presented. Inelastic acoustic phonon, polar optical phonon and ionized impurity scattering are considered in the bulk formalism. The model has been applied on GaAs/GaAlAs superlattice simulation with one miniband for gamma electrons. The simulation is performed by different conditions defined by temperature, electric field and ionized impurity concentration. Bloch oscillations of miniband electrons with different lifetimes, frequencies and amplitudes are observed in the simulation results