Many particle approach to excitons in crystals: Electron–electron and electron–phonon interactions

A many particle system of electrons interacting one with another and also with the crystal lattice vibrations was studied theoretically. The particular diagonalization of the Hamiltonian was fulfilled and it was shown that the structure of bands (exciton structure) in the absorption spectra of the crystal is really the set of electron–phonon maxima. Numerical calculations showed also that full electron bands, valence and conductivity, are responsible for the formation of exciton maxima and even states located far from the edge of zones have significant effect on the occurrence of exciton peaks – which is in disagreement with the effective mass approximation (EMA). The results are compared with known experimental data for wide band ZnO and CdS crystals.