Strong Generation of Coherent Acoustic Phonons in Semiconductor Quantum Dots

We present experimental results obtained in two-color pump-probe experiments performed in semiconductor self-assembled quantum dot (QD) layers. The sample reflectivities present several acoustic contributions, among which are strong acoustic phonon wave packets. A comparison between one- and two-color experiments and a fine analysis of the echo shape attest that a high magnitude phonon pulse emerges from each single QD layer. This conclusion is supported by a numerical modeling which perfectly reproduces our experimental signals only if we introduce a strong generation in each QD layer. We explain such a strong emission thanks to an efficient capture of the carriers by the QDs.