1,242 research outputs found
Transport in semiconductor superlattices: from quantum kinetics to terahertz-photon detectors
Semiconductor superlattices are interesting for two distinct reasons: the
possibility to design their structure (band-width(s),doping, etc.) gives access
to a large parameter space where different physical phenomena can be explored.
Secondly, many important device applications have been proposed, and then
subsequently successfully fabricated. A number of theoretical approaches has
been used to describe their current-voltage characteristics, such as miniband
conduction, Wannier-Stark hopping, and sequential tunneling. The choice of a
transport model has often been dictated by pragmatic considerations without
paying much attention to the strict domains of validity of the chosen model. In
the first part of this paper we review recent efforts to map out these
boundaries, using a first-principles quantum transport theory, which
encompasses the standard models as special cases. In the second part, focusing
in the mini-band regime, we analyze a superlattice device as an element in an
electric circuit, and show that its performance as a THz-photon detector allows
significant optimization, with respect to geometric and parasitic effects, and
detection frequency. The key physical mechanism enhancing the responsivity is
the excitation of hybrid Bloch-plasma oscillations.Comment: 22 pages, 10 figures, uses lamuphys.sty (included); to appear in the
Proceedings of the XVI Sitges Conference, Statistical and Dynamical Aspects
of Mesoscopic Systems (Lecture Notes in Physics, Springer
Pulse interaction in nonlinear vacuum electrodynamics
The energy-momentum conservation law is used to investigate the interaction
of pulses in the framework of nonlinear electrodynamics with Lorentz-invariant
constitutive relations. It is shown that for the pulses of the arbitrary shape
the interaction results in phase shift only.Comment: LaTeX, 5 pages, 2 EPS figure
Current responsivity of semiconductor superlattice THz-photon detectors
The current responsivity of a semiconductor superlattice THz-photon detector
is calculated using an equivalent circuit model which takes into account the
finite matching efficiency between a detector antenna and the superlattice in
the presence of parasitic losses. Calculations performed for currently
available superlattice diodes show that both the magnitudes and the roll-off
frequencies of the responsivity are strongly influenced by an excitation of
hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system
in the THz- frequency band. The expected room temperature values of the
responsivity (2-3 A/W in the 1-3 THz-frequency band) range up to several
percents of the quantum efficiency of an ideal superconductor
tunnel junction detector. Properly designed semiconductor superlattice
detectors may thus demonstrate better room temperature THz-photon responsivity
than conventional Schottky junction devices.Comment: Revtex file, uses epsf, 11 pages. 11 eps-figures; EPS-files generated
by scanner, original higher resolution line drawings available from
[email protected] by regular mail or fa
Rotational kinetics of absorbing dust grains in neutral gas
We study the rotational and translational kinetics of massive particulates
(dust grains) absorbing the ambient gas. Equations for microscopic phase
densities are deduced resulting in the Fokker-Planck equation for the dust
component. It is shown that although there is no stationary distribution, the
translational and rotational temperatures of dust tend to certain values, which
differ from the temperature of the ambient gas. The influence of the inner
structure of grains on rotational kinetics is also discussed.Comment: REVTEX4, 20 pages, 2 figure
Fractional and unquantized dc voltage generation in THz-driven semiconductor superlattices
We consider the spontaneous creation of a dc voltage across a strongly
coupled semiconductor superlattice subjected to THz radiation. We show that the
dc voltage may be approximately proportional either to an integer or to a half-
integer multiple of the frequency of the applied ac field, depending on the
ratio of the characteristic scattering rates of conducting electrons. For the
case of an ac field frequency less than the characteristic scattering rates, we
demonstrate the generation of an unquantized dc voltage.Comment: 6 pages, 3 figures, RevTEX, EPSF. Revised version v3: corrected typo
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