Electronic Properties Associated with Donor Impurities in Multivalley Semiconductors

In this thesis we treat the theory of the electronic properties of excitons bound to a neutral donor in multivalley semiconductors. The materials considered here are Si, Ge and GaP. To deal with the effect of realistic band structures on the excitons bound to a neutral donor, we proceed in a systematic way by studying first the effects of the valley-orbit interactions on the donor states, then the energy levels of the low-lying states (including fine structures produced by the interparticle interactions) for the donor bound excitons, and finally the excitation spectroscopy for the bound multiexciton complexes (BMEC) associated with donors. In the calculation of the valley-orbit interactions for the donor states, we have included the intervalley scattering effect for both the kinetic and potential energy terms . We find that the inclusion of intervalley kinetic energy term (which has been frequently ignored in the existing literature) is essential to stabilize the system (i.e., keep the donor states from being deep), To apply the valley-orbit interactions to more complicated systems, donor bound excitons and BMEC's, we have developed model Hamiltonians (one for each symmetry associated with the Td point group) which yield analytic expressions for the matrix elements and produce practically the same energy eigenvalues as that of the exact donor Hamiltonian.