Free-carrier absorption in quantum cascade structures

Abstract

Free-carrier absorption in quantum cascade structuresCarosella, F.; Ndebeka-Bandou, C.; Ferreira, R.; Dupont, E.; Unterrainer, K.; Strasser, G.; Wacker, Andreas; Bastard, G. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We show that the free-carrier absorption in quantum cascade lasers (QCLs) is very small and radically different from the classical Drude result due to the orthogonality between the direction of the carrier free motion and the electric field of the laser emission. A quantum mechanical calculation of the free-carrier absorption and intersubband oblique absorption induced by interface defects, Coulombic impurities, and optical phonon absorption/emission is presented for QCLs with a double-quantum-well design. The interaction between the electrons and the optical phonons dominates at room temperature.

Injection terahertz laser using the resonant inter-layer radiative transitions in double-graphene-layer structure

“…Similar situation takes place in the quantum cascade lasers (QCLs) based on multiple quantum well (MQW) structures [12]. However, in the case of the photon polarization perpendicular to the QW plane the intraband (intrasubband) absorption can be much weaker than that following from the semi-classical Drude formula [13].In this paper, we propose a device structure based on a double-GL structure shown in Fig. 1 (upper panel) with the injection of electrons to one n-doped GL and to another p-doped GL, which can be used for lasing of THz photons with the electric field perpendicular to the GL plane due to the tunneling inter-GL radiative processes.…”

“…Similar situation takes place in the quantum cascade lasers (QCLs) based on multiple quantum well (MQW) structures [12]. However, in the case of the photon polarization perpendicular to the QW plane the intraband (intrasubband) absorption can be much weaker than that following from the semi-classical Drude formula [13].…”

Free-carrier absorption in asymmetric double quantum well structures due to static scatterers in the in-plane polarization

“…We shall also demonstrate that FCA can be larger in the in-plane polarization that in the z-polarization. Finally, we shall show that the intrasubband FCA is more important than the inter-suband one, a feature that again differs from what happens in the z-polarization analyzed previously 12 . In the following, we concentrate on the optical intraand inter-subband transitions mediated by static scatterers such as interface defects, Coulombic donors and alloy disorder, and we show that the dependance of the FCA upon the photon energy is significantly modified by the polarization of the electromagnetic wave.…”

“…For comparison, we computed the energy loss rate in the z-polarization configuration, following the quantum mechanical treatment of FCA established in Ref. 12. The results are shown in Fig.…”

“…FCA arises from intra-subband and inter-subband oblique transitions 11 (in the k space) activated by static scatterers or phonons. Recently, we proposed a modeling of FCA in QCL's 12 , thereby focusing our attention on the standard light polarization for these systems, i.e, electromagnetic waves that propagate in the layer plane with their electric vector parallel to the growth axis. In this paper we examine the case of an electromagnetic wave that propagates along the (z) growth axis with its electric vector laying in the layer plane.…”