Sequential multi-photon strategy for semiconductor-based terahertz detectors

A semiconductor-based terahertz-detector strategy, exploiting a bound-to-bound-to-continuum architecture, is presented and investigated. In particular, a ladder of equidistant energy levels is employed, whose step is tuned to the desired detection frequency and allows for sequential multi-photon absorption. Our theoretical analysis demonstrates that the proposed multi-subband scheme could represent a promising alternative to conventional quantum-well infrared photodetectors in the terahertz spectral region.Comment: Submitted to Journal of Applied Physic

Terahertz detection schemes based on sequential multi-photon absorption

We present modeling and simulation of prototypical multi bound state quantum well infrared photodetectors and show that such a detection design may overcome the problems arising when the operation frequency is pushed down into the far infrared spectral region. In particular, after a simplified analysis on a parabolic-potential design, we propose a fully three-dimensional model based on a finite difference solution of the Boltzmann transport equation for realistic potential profiles. The performances of the proposed simulated devices are encouraging and support the idea that such design strategy may face the well-known dark-current problem.Comment: 3 pages, 2 figures; submitted to Applied Physics Letter

Design and Simulation of THz Quantum Cascade Lasers

Strategies and concepts for the design of THz emitters based on the quantum cascade scheme are analyzed and modeled in terms of a fully three-dimensional Monte Carlo approach; this allows for a proper inclusion of both carrier-carrier and carrier-phonon scattering mechanisms. Starting from the simulation of previously published far-infrared emitters, where no population inversion is achieved, two innovative designs are proposed. The first one follows the well-established chirped-superlattice scheme whereas the second one employs a double-quantum well superlattice to allow energy relaxation through optical phonon emission. For both cases a significant population inversion is predicted at temperatures up to 80 K.Comment: 4 pages, 2 figures, 2 table

Monte Carlo Kinetic Modeling of the Combined Carrier-Phonon Nonequilibrium Dynamics in Semiconductor Heterostructure Devices

Electron-phonon interaction is a key mechanism for charge and heat transport in both bulk materials as well as in state-of-the-art electronic and optoelectronic solid-state devices. Indeed, that of an effective heat dissipation, at the diverse design levels, has always been a primary issue in device operation and performances. In various circumstances, the charge carrier subsystem happens to be coupled to a significant nonequilibrium optical phonon population. This regime may be particularly pronounced in new-generation quantum emitters based on semiconductor heterostructures and operating both in the mid-infrared as well as in the terahertz region of the electromagnetic spectrum. In this chapter, we review a global kinetic approach based on a Monte Carlo simulation technique that we have recently proposed for the modeling of the combined carrier-phonon nonequilibrium dynamics in realistic unipolar multisubband device designs. Results for the case of a prototypical resonant-phonon terahertz emitting quantum cascade laser are shown and discussed

Quantum theory of transient transport in semiconductors: A Monte Carlo approach

A new Monte Carlo method is presented for the evaluation of the density matrix from the solution of the Liouville–von Neumann equation for an ensemble of noninteracting electrons in a semiconductor crystal. The method is applied to the study of the electron transient response to a high external electric field in Si and to the relaxation of photoexcited electrons in GaAs in absence of external electric fields. The phonon population is always assumed at equilibrium, but no assumptions are made about the strength of the electron-phonon interaction. Results show that typical quantum features such as energy-nonconserving transitions, intracollisional field effect, and multiple collisions change the very first transient of the system with respect to a semiclassical description

Aspects of magnetopause/magnetosphere response to interplanetary discontinuities, and features of magnetopause Kelvin-Helmholtz waves

We describe (i) perturbations of the magnetopause/magnetosphere elicited by an interplanetary discontinuity and (ii) the production of Kelvin-Helmholtz waves on the magnetopause. These are two large topics, so for reasons of space we combine both features in a single data example, supporting the observations by theory. Correspondingly, the observations, made by ACE, consist of an interval in which a current sheet is followed by a period of strongly northward IMF. In view of recent attention directed at the effect of variations of the azimuthal component of the solar wind velocity on the magnetosphere, we chose a current sheet (CS) across which the east-west components of both field and flow vectors change polarity. A two-stage response is evident in the records of Cluster, outbound at the dusk terminator at 27° MLAT: (i) Four cycles of large-amplitude, ~3min oscillations during which the spacecraft sample alternately the cold, dense magnetosheath and the hot and tenuous magnetosphere plasmas. We argue that these motions are likely due to tangential stresses applied to the magnetopause. (ii) Soon thereafter the oscillatory character changes dramatically, and ~80s small-amplitude undulations appear which we argue to be magnetopause surface waves. Applying linear MHD theory we show these waves are due to a locally Kelvin-Helmholtz unstable boundary. As input parameters, we take values during the preceding large oscillations at the same magnetopause locale. An aspect of the non-linear phase of this instability is illustrated by a numerical simulation: the reduced duration of the evolution into large vortices by a strong initial perturbation.Fil: Farrugia, C. J.. University Of New Hampshire; Estados UnidosFil: Gratton, Fausto Tulio Livio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Fisicomatemáticas e Ingeniería; Argentin

Improving the operation temperature of semiconductor-based Terahertz photodetectors: A multiphoton design

We propose and theoretically investigate a semiconductor-based terahertz-detector design exploiting a multiphoton absorption strategy through a bound-to-bound-to-continuum scheme. Our results demonstrate that such a multisubband architecture may access values of the background-limited infrared photodetection temperature, significantly higher than those of conventional quantum well infrared photodetectors operating at the same frequency, and therefore could represent a better alternative to the latter in the terahertz spectral region

Quantum theory of impact ionization in coherent high-field semiconductor transport

Generation of carriers in semiconductors by impact ionization is studied under the influence of a constant, arbibrarily high electric field. Using the density-matrix approach a system of equations for the coherent dynamics of electrons and holes in the presence of impact ionization and Auger recombination is derived, which extends the semiconductor Bloch equations by the inclusion of impact-ionization density-correlation functions as additional dynamic variables. From these equations we recover the pure (Zener) and the photon-induced (Franz-Keldysh) carrier tunneling rate and derive an expression for the field-assisted impact-ionization scattering rate. Different levels of approximation of the kinetic equations are discussed. It is shown that in contrast to the semiclassical treatment in the presence of an electric field, a fixed impact-ionization threshold does no longer exist, and the impact-ionization scattering rate is drastically enhanced around the semiclassical threshold by the intracollisional field effect. The close connection of field-assisted impact ionization to the Franz-Keldysh effect is emphasized