Observation of the second‐nearest‐neighbor Bloch oscillation in a GaAs/AlAs superlattice

Abstract

AbstractWe have systematically investigated the quantum beat of the miniband excitons and the Bloch oscillation in the Wannier‐Stark (WS) localization as a function of applied bias voltage in a GaAs (6.8 nm)/AlAs (0.9 nm) superlattice embedded in a p ‐i ‐n diode structure. The coherent dynamics behaviors were detected with a reflection‐type pump‐probe technique. We clearly observed the transformation process from the miniband‐exciton quantum beat to the Bloch oscillation with an increase in applied bias voltage producing an internal electric field. The noteworthy finding is the fact that the Bloch oscillation with the frequency of vBO = 2eFD /h appears in a weak localization regime in addition to the usual Bloch oscillation with vBO = eFD /h in a strong localization regime, where F is the electric field, and D is the superlattice period. The frequency of 2eFD /h indicates that the newly observed Bloch oscillation is due to the wave‐packet motion in the second‐nearest‐neighbor space range. The results described above are explained by the electric‐field‐strength dependence of the envelope‐function localization, which is estimated from the envelope‐function profile calculated by a transfer‐matrix method and the excitonic transitions observed by electroreflectance spectroscopy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)