Disentangling the role of wave function overlap, exciton–exciton interaction, carrier confinement and shape in the properties of spherical quantum wells

There is a widespread conviction, fuelled by simple effective mass theoretical modelling, that the enhanced optical properties of quantum shells (i.e., CdS/CdSe/CdS core/shell in a shell structures) derive from a combination of relaxed carrier confinement, decreased overlap between electron and hole wave functions, reduced Coulomb interaction between photoinduced charge carriers and exciton–exciton repulsion, achieved in these nanoscopic spherical quantum wells (SQWs) by shape engineering. Confirming the origins of such properties by means of a more sophisticated theoretical framework is however important to ensure that future efforts at further improvement do not pursue the wrong strategy. Using the atomistic semiempirical pseudopotential method, we show that most of the assumptions behind such effects are incorrect, and that the origins of the peculiar optical properties of quantum shells are to be found elsewhere.