Exciton Energy Levels in Wurtzite-Type Crystals

The exciton problem in wurtzite-type crystals is investigated taking into full account the structure of the valence bands. Using perturbation theory, after a proper rotation of the exciton Hamiltonian, we obtain analytical expressions for the exciton ground states originating from the ${\Gamma }_9$, ${\Gamma }_7$, and ${\Gamma }_7$ valence subbands. These expressions are valid for any value of the crystal field splitting. Results are given for CdSe and CdS and the agreement with experiment is good.