Enhanced Electron-Phonon Interaction in InAs/GaAs Self-Assembled Quantum Dots

摘要

Self-assembled InAs/GaAs quantum dots (SADs) when characterized by selective photoluminescence (PL) show multiple phonon-assisted radiative bands. Intradot relaxation has thusfar been assumed to be responsible for these spectral features. However, we found that no real crystal states are involved in the experimentally observed phonon meission. Under non-resonant excitation at 5K the SADs photoluminescence band is centered at 1.315 eV. This suggests that the dots in our samples are small enough to have no excited levels. Indeed, as proven by photoluminescence experiments at high excitation densities, there are no excited states in our dots. In spite of the fact that we deal with the small dots, the selective PL measurements do show strong phonon-assisted bands. We interpret the phonon-assisted PL as being due to the Frohlich interaction between strain-induced polarized excitons in the SADs and LO-phonons. The model is consistent with our micro-PL measurement as well as the pronounced p-type polarization of the emission observed in our cleaved-side PL-measurements. Further support is obtained from our calculations in which a different localization of the electrons and holes is assumed: The limiting case of this theoretical framework gives a Huang-Rhys factor of approx0.2, which compares nicely with the experiments.