Theory of Spin Orientation of Semiconductor Carriers at a Ferromagnetic Interface

A quantum theory of the spin-dependent scattering of semiconductor electrons by a Schottky barrier at an interface with a ferromagnet is presented. The reflection of unpolarized non-equilibrium carriers produces spontaneous spin-polarization in the semiconductor. If a net spin-polarization pre-exists in the semiconductor, the combination of the ferromagnet magnetization and the incident carrier polarization combine to tilt the reflected polarization in the semiconductor. The spin reflection properties are investigated as functions of the system characteristics: the Schottky barrier height, semiconductor doping and applied bias. The effect on reflection due to the variation of the barrier width with electron energy is contrasted for two means of excitation: optical or electrical. Optically excited electrons have a wider energy spread than the near-equilibrium excitation from non-magnetic ohmic contacts.