Available online at http://www.idealibrary.com on Article No. spmi.1999.0763 Superlattices and Microstructures, Vol. 26, No. 2, 1999 Inﬂuence of carrier–carrier scattering on intraband dephasing F. WOLTER, R. MARTINI , S. TOLK, P. HARING BOLIVAR, H. KURZ Institut f¨ ur Halbleitertechnik II, RWTH Aachen, Sommerfeldstraße 24, D-52056 Aachen, Germany R. HEY , H. T. GRAHN Paul Drude Institut f¨ ur Festk¨ orperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin, Germany (Received 7 May 1999) The inﬂuence of carrier–carrier scattering on intraband coherence is studied by analyz- ing the dephasing of the THz emission from optically excited Bloch oscillations in a GaAs/AlGaAs superlattice. Intercarrier collision-induced dephasing is investigated by varying both the density of coherent scattering partners as well as the density of an inco- herent carrier background. Both situations yield homogeneous linearly density-dependent contributions. Dephasing due to an incoherent background density is shown to be twice as efﬁcient as scattering by coherent carriers. The efﬁciency of incoherent scattering is shown to depend moderately on the time delay to the pre-pulse generating the background density. c  1999 Academic Press Key words: carrier–carrier scattering, intraband dephasing. 1. Introduction Many applications of coherent electronic transport or coherent wavepacket oscillations in semiconductor heterostructures have been demonstrated. A prominent example are Bloch oscillations (BO) of electronic wavepackets in semiconductor superlattices, which was proposed by Esaki and Tsu as coherent tunable sources of electromagnetic radiation in the Terahertz (THz) frequency range [1]. When a superlattice is sub- jected to a dc bias, electrons in the superlattice minibands oscillate with a characteristic frequency ν B = eFd h , where F denotes the bias ﬁeld and d the superlattice period. Different ultrafast experimental techniques have been used to investigate this phenomenon in the time domain [2–5] and a frequency tunability between 0.2 and 10 THz was demonstrated. One of the attractive applications of BO is the emission of coherent and frequency-tunable THz radiation connected with the spatial oscillation [3]. Nevertheless, despite the super- radiant properties of a coherently emitting ensemble of carriers performing BO, only extremely low conver- sion efﬁciencies on the order of 3 × 10 −8 have been achieved [6]. The main problem restricting the efﬁciency of the emission from this coherent intraband carrier oscillation is the rapid loss of coherence, i.e. dephas- ing of the emitting ensemble. Therefore the quadratic scaling of the emitted THz energy with the excitation density is strongly reduced at higher carrier densities due to many-body (carrier–carrier) scattering effects. Even at small excitation densities around 2 × 10 9 cm −2 per well the coherent emission is strongly damped with time constants around 1 ps. This discussion illustrates the importance of studying and understanding dephasing before coherent electronic wavepacket dynamics can be put to practical use. 0749–6036/99/080093 + 10 $30.00/0 c  1999 Academic Press