Semiconductor superlattices as terahertz generators

Abstract

Avoiding any truncation of the Hamiltonian for independent electrons in both ideal and imperfect superlattices subject to a uniform electric field, we show that dipole radiation in the terahertz range should be detectable for many members of the GaAs/Al"Ga& "Assystem. The radition can be attributed to periodic Bloch oscillations in the case of ideal superlattices, and to almost-periodic oscillations, with the dominant frequencies on the order of the Bloch frequency, in the case of imperfect superlattices.

Extended states and dynamical localization in semiconductor superlattices

“…Moreover, Bouchard and Luban found that BOs are not periodic but instead they become almost-periodic oscillations in SLs with GaAs contaminated by excess Al. 1 Thus, it seems that small fluctuations of local potentials cannot completely destroy BOs. This can be understood from the fact that the localization effects of disorder are not very strong and, consequently, signatures of BOs still occur in those SLs.…”

“…Recently, GaAs-Ga 1Ϫx Al x As SLs operating as terahertz generators have been proposed. 1 The origin of the electromagnetic radiation is attributed to periodic and almost-periodic Bloch oscillations 2 ͑BOs͒ in perfect and imperfect systems, respectively. The idea of semiconductor SLs radiating at terahertz frequencies was proposed some time ago by Esaki and Tsu, 3 who argued that electrons should undergo BOs.…”

Dephasing effects induced by weak disorder in superlattices

“…In this regard, Plessen et al [11] found that quantum coherence is lost after few BO's in 30 GaAs / 30 Ga Al As SL's, which was 0.7 0.3 attributed to scattering by LO phonons. On the other hand, theoretical studies point out that under most experimental conditions interminiband transitions are negligible and, consequently, cannot be responsible for the signal decay Bouchard [1]. Furthermore, Plessen et al [11] conclude from their experimental results that the critical electric fiel F is higher for SL's with D larger than the energy c of LO phonons, E 5 36 meV.…”

“…We stress that, according to Bouchard and Luban [1] the dynamical behavior of this initial state is similar to that of more realistic functions. The solution of Eq.…”

“…We show that the lifetime of Bloch oscillations is controlled by a characteristic time which depends on the degree of disorder and is independent of the electric field This result is further supported by the excellent agreement between our model calculations and several recent experiments, and leads to specifi new predictions.Keywords: Superlattices; Bloch oscillations; Disorder; Dephasing mechanisms Dynamical effects in quantum-well semiconductors superlattices (SL's) are the basis for designing ultra-high speed electronic devices, as have been recently proposed [1]. This idea of semiconductor SL's operating at terahertz frequencies was already suggested a long time ago by Esaki and Tsu [2], who argued that electrons should undergo periodic Bloch oscillations (BO's) [3,4]: Under an applied electric fiel F, electrons oscillate in real space as well as in k space with a characteristic period given by t 5 2p" /eFd, d being the spatial period of the SL [5][6][7].…”