  We discuss level schemes of small quantum-dot turnstiles and their
applicability in the production of entanglement in two-photon emission. Due to
the large energy splitting of the single-electron levels, only one single
electron level and one single hole level can be made resonant with the levels
in the conduction band and valence band. This results in a model with nine
distinct levels, which are split by the Coulomb interactions. We show that the
optical selection rules are different for flat and tall cylindrically symmetric
dots, and how this affects the quality of the entanglement generated in the
decay of the biexciton state. The effect of charge carrier tunneling and of a
resonant cavity is included in the model.
