Full band structure calculations of optical spin injection in Si and CdSe

We present a theoretical study of optical electron spin injection (optical orientation) in the bulk semiconductors Si and CdSe from direct optical excitation with circularly polarized light.\footnote{F. Nastos, J. Rioux, M. Strimas-Mackey, B.S. Mendoza, and J.E. Sipe, Phys. Rev. B \textbf{76}, 205113 (2007).} To describe excitation at energies significantly above the band edge, we use full-zone band structures from pseudopotential calculations. For Si, 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. Averaging over crystal orientation gives a 50\% spin polarization for band edge excitation.