Coherent phonons in a doped GaAs/AlAs superlattice

Abstract

In this paper we report the excitation and detection of coherent zone-folded longitudinal phonons in a n-doped AlAs/GaAs superlattice using femtosecond pump-probe measurements. Oscillations in the probe reflectance were observed at a frequency of about 440 GHz, which is the frequency of the first mini-zone centre phonon mode. By applying an electrical bias across the superlattice, the intensity of the oscillations was increased when the energy drop per period of the superlattice was approximately equal to the energy of the first mini-zone centre mode. We attribute this observation to phonon amplification occurring in the superlattice. © 2007 IOP Publishing Ltd.