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 $e/\hbar\omega$ 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