Exciton dephasing via phonon interactions in InAs quantum dots: Dependence on quantum confinement

We report systematic measurements of the dephasing of the excitonic ground-state transition in a series of InGaAs/GaAs quantum dots having different quantum confinement potentials. Using a highly sensitive fourwave mixing technique, we measure the polarization decay in the temperature range from 5 to 120 K on nine samples having the energy distance from the dot ground-state transition to the wetting layer continuum sconfinement energyd tuned from 332 to 69 meV by thermal annealing. The width and the weight of the zerophonon line in the homogeneous line shape are inferred from the measured polarization decay and are discussed within the framework of recent theoretical models of the exciton-acoustic phonon interaction in quantum dots. The weight of the zero-phonon line is found to decrease with increasing lattice temperature and confinement energy, consistently with theoretical predictions by the independent Boson model. The temperature-dependent width of the zero-phonon line is well reproduced by a thermally activated behavior having two constant activation energies of 6 and 28 meV, independent of confinement energy. Only the coefficient to the 6-meV activation energy shows a systematic increase with increasing confinement energy. These findings rule out that the process of one-phonon absorption from the excitonic ground state into higher energy states is the underlying dephasing mechanism.