Vertical stacks of small InAs/GaAs self-assembled dots:: resonant and non-resonant excitation

We have performed photoluminescence experiments in samples containing self-assembled quantum dots with different spacer layer thicknesses.. A strong filtering effect produced by the GaAs spacer layer on the dots size being stacked is observed for spacers thinner than 10 nm. This effect produces a blue shift of the emission band from stacked dots and A simultaneous line width narrowing. At the same time, given the existence of a broad dot size distribution in the first layer; bigger dots can evolve towards InAs cylinder-like structures, whose emission occurs at appreciably lower energies as compared to the emission band associated to dot stacks (with some GaAs separation). (C) 2002 Elsevier Science B.V. All rights reserved.