Energy relaxation of electrons inInAs∕GaAsquantum dot molecules

The photoluminescence emission intensities of the exciton states in $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ coupled quantum dots are studied with regard to the tunneling-induced dependence on splitting energy. Even at very low excitation, emission from bonding and antibonding states is observed, as long as the splitting ranges between a few and $\sim 30\mathrm{meV}$. As the splitting is dominated by the conduction band states, this demonstrates an acoustic-phonon relaxation bottleneck for electrons. For larger splittings, only bonding state emission is observed at low excitation, indicating fast carrier relaxation, which is most likely caused by a combination of electron-hole scattering and polaron formation.