Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations (original) (raw)
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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.
Superradiant emission from Bloch oscillations in semiconductor superlattices
Physical review. B, Condensed matter, 1996
The superradiant character of submillimeter-wave emission from optically excited electronic Bloch oscillations in a GaAs/Al x Ga 1Ϫx As superlattice is investigated by time-resolved terahertz emission spectroscopy. The intensity of the radiation and its decay time are studied as a function of the density of excited charge carriers. From the measured emission efficiency, the spatial amplitude of the charge oscillations is estimated.
Nanohelices as superlattices: Bloch oscillations and electric dipole transitions
Physical Review B
Subjecting a nanohelix to a transverse electric field gives rise to superlattice behavior with tunable electronic properties. We theoretically investigate such a system and find Bloch oscillations and negative differential conductance when a longitudinal electric field (along the nanohelix axis) is also applied. Furthermore, we study dipole transitions across the transverse-electric-field-induced energy gap, which can be tuned to the eulogized terahertz frequency range by experimentally attainable external fields. We also reveal a photogalvanic effect by shining circularly polarized light onto our helical quantum wire.
Semiconductors Engl Tr, 2001
It is demonstrated that the electron spectrum in ideal two-dimensional and three-dimensional quantum-dot superlattices (SLs) under a constant electric field can be either discrete or continuous depending on the field orientation with respect to the SL crystallographic axes. In the latter case, the width of the resulting transverse miniband depends exponentially on the crystallographic index corresponding to the direction of the field. The electron localization area undergoes dramatic variations with the field orientation in the vicinity of the directions corresponding to the continuous energy spectrum. The Bloch oscillations in this kind of SL are considered. It is established that the scattering of oscillating electrons can be strongly suppressed by an appropriate choice of the field strength and direction.
Zener tunneling in superlattices in a magnetic field
Physical Review B
We present a study of the Zener effect in the optical absorption of strongly coupled superlattices with both a magnetic and an electric field in growth direction. The in-plane continuum of electron states is discretized due to Landau quantization, which allows to directly observe the transition from discrete to continuum states due to Zener tunneling in a true 1D system.
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.
physica status solidi (b), 1997
The absolute spatial displacement of Bloch-oscillating electrons in semiconductor superlattices is measured as a function of time with a few angstrom resolution using a novel experimental technique: The oscillating Bloch wave packet creates a small dipole field which can be determined using the field shift of the Wannier-Stark ladder transitions as a sensitive detector. The total amplitudes and their dependence on the static electric field are in good agreement with a theory including excitonic effects.