Full band structure LDA and k∙p calculations of optical spin-injection

We present a study of optical electron spin-injection (optical orientation) in the bulk semiconductors GaAs, Si, and CdSe from direct optical excitation with circularly polarized light. For GaAs and Si, we compare pseudopotential calculations with calculations of a recent full-zone k∙p model. For GaAs, we find that there can be up to 30% spin-injection at energies well above the band gap. For Si, which has very weak spin-orbit coupling, we find that there can be up to 30% spin polarization from direct transitions. The relatively low symmetry of wurtzite CdSe leads to an orientation dependent spin-injection, which can be up to 100% polarized at the band edge. For each of these systems, full-zone calculations are made, which allow us to consider excitation well above the band gap. An adaptive Brillouin zone sampling scheme is used, which allows us to obtain rapid convergence of our spectra. A derivation of the spin-injection rate, which accounts for the coherences excited in a semiconductor with spin-split bands, is also included.