Excitonic fine structure of zinc-blende and wurtzite colloidal CdSe nanocrystals and comparison to effective mass results

Abstract

We study the excitonic fine structure of CdSe nanocrystals (also known as quantum dots) using atomic effective pseudopotentials in combination with the screened configuration interaction method, and we obtain excellent agreement with experiment. The direct comparison between atomistic and effective mass results reveals qualitative differences that become apparent almost as soon as confinement effects start to play a role, i.e., for the experimentally most relevant sizes. We proceed with a comparison of the wurtzite and zinc-blende fine structure as a function of size and ellipticity. We show that the absorption of significantly oblate zinc-blende nanocrystals can be very similar to ``spherical'' wurtzite nanocrystals. On the other hand, if the nanocrystals have no ellipticity but different crystal structures, the fine structure differs significantly. Conversely, structures with high ellipticity, either oblate or prolate, with different crystal structures show similar fine structures.