  Understanding the optical emission characteristics of semiconductor
nanostructures is important when determing their device applicability. The
emission depends on the material and its geometry, but also depends on other
processes such as thermal escape from the nanostructure. Although it is widely
accepted that scattering involving longitudinal optical phonons is the key
process in thermal escape, it remains unclear why some quantum structures
thermally emit excitons and other single charge carriers. To investigate this
phenomena we theoretically determine the energy levels and temperature-lifetime
relationships of quantum dots and rings. We find that replicating the observed
temperature dependence of the exciton lifetime requires both an eigenspectrum
and a thermal escape mechanism which are geometry dependent. This suggests that
geometry may be a significant factor in determining the dominant thermal escape
process in quantum structures.
