Fröhlich interaction in InAs/GaAs self-assembled quantum dots

The phonon bottleneck in self-assembled InAs/GaAs quantum dots (SAD’s) is observed directly in continuous-wave photoluminescence experiments when exciting one GaAs longitudinal optical (LO)-phonon energy above the ground level of the smallest dot. To overcome the phonon bottleneck, selective photoluminescence (PL) experiments are performed and multiple phonon-assisted radiative bands are observed. We found that no real crystal states are involved in the experimentally observed phonon emission. Under nonresonant excitation at 5 K, the SAD’s photoluminescence band is centered at 1.315 eV. As proven by our photoluminescence experiments at high excitation densities, there are no excited states in such small dots. We interpret the phonon-assisted PL as being due to enhanced Fröhlich interaction between strain-induced polarized excitons in the SAD’s and LO phonons. Further experimental support for this model is found from the cleaved-side PL measurements. A light-hole ground state is observed, instead of the theoretically predicted heavy-hole one.