Conditions for efficient spin injection from a ferromagnetic metal into a semiconductor

We adapt the spin accumulation model of the perpendicular transport in metallic magnetic multilayers to the issue of spin injection from a ferromagnetic metal (F) into a semiconductor (N). We show that the problem of the conductivity mismatch between F and N can be solved by introducing a spin dependent interface resistance (tunnel junction preferably) at the (formula presented) interfaces. In the case of a (formula presented) structure, a significant value of the magnetoresistance can be obtained if the junction resistance at the (formula presented) and (formula presented) interfaces is chosen between two threshold values depending on the resistivity, spin diffusion length and thickness of N. The problem is treated for various geometries (vertical or lateral (formula presented) structures).