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 $\mathbf{k}\cdot \mathbf{p}$ 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 $\mathrm{QD}\mathrm{’}\mathrm{s}\hspace{0.5em}{(E}_{\det }\lesssim 1.1\mathrm{eV}),$ 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.