Impact of traveling phonon wave packets on the optical response of quantum dots

Huneke J, Kuhn T, Axt VM, Machnikowski P

Abstract

The influence of phonon wave packets created by the optical excitation of a quantum dot (QD) structure on four-wave-mixing (FWM) signals is analyzed theoretically. Two different structures are compared: a single QD in a half-space geometry located close to the surface, where the emitted phonon wave packet after reflection at the surface reenters the QD and a pair of QDs in an infinite medium, where the phonon wave packet created in one QD travels across the other QD. Although the strain fields are very similar pronounced differences in the FWM polarizations are found. In the single QD system we observe clear signatures of the reflected wave packet in the FWM signal at positive delay times, which can also be observed in the time-integrated FWM signal from an inhomogeneously broadened ensemble of such QDs. In the two QD case no signatures of the traveling wave packet are seen in the signal at positive delays and, consequently, in the ensemble signal. However, they are clearly seen in the FWM signal at negative delay times.