The appearance of localized resonances above the continuum in quantum dots

We investigate the nature of hole and electron states in self-assembled InAs/GaAs and (In,Ga)As quantum dots, using a multi-band atomistic pseudopotential approach. We offer a classification of both hole and electron states based on an analysis of their localization both in the $z$ and $xy$-directions. We show that the coherent dot-matrix strain present in self-assembled quantum dots distorts the electron confining potential, creating ``wings'' in the vicinity of the dot. This results in the appearance of dot-confined electronic states that lie above the continuum of the matrix material. The spectroscopic manifestation of these resonant states is investigated, by calculating the inter-band as well as the intra-band absorption spectra. We find, in both cases, that clear finger-prints of the resonances appear, in the form of sharp, well-defined peaks. In contrast, the previously suggested ``cross-transitions'' between wetting-layer states and dot states are shown to disappear once realistic strain is included.