Quantum size effect in self-organized InAs/GaAs quantum dots

The quantum size effect of exciton transitions is investigated experimentally and theoretically for self-organized InAs/GaAs quantum dots (QD's). Photoluminescence excitation (PLE) experiments are reported for a series of samples with QD's varying in average size, revealing size-dependent excitation resonances. Temperature-dependent measurements show that the PLE spectra mirror the absorption spectra of QD's with a certain ground state transition energy. The observed PLE resonances are identified based on their energy, relative intensity, and sensitivity to size variations in comparison to results of eight-band k·p calculations for pyramidal InAs/GaAs QD's with {101} side facets. Band mixing, strain, and the particular geometry of the three-dimensional confinement lead to a rich fine structure with a variety of ``forbidden'' excitonic transitions. A good agreement between experiment and theory is found for large QD's (Edet1.1eV), whereas the agreement becomes worse for smaller QD's. The discrepancies arise, most likely, from the uncertainties in the size- and growth-dependent variations of the QD shape and composition as well as Coulomb-induced localized wetting layer states.