Efficient spin extraction from nonmagnetic semiconductors near forward-biased ferromagnetic-semiconductor modified junctions at low spin polarization of current

We study tunneling of electrons from nonmagnetic semiconductors (S) into ferromagnets (FM) through a Schottky barrier modified by a very thin heavily doped interfacial layer. It is shown that in such forward-biased FM-S junctions, the electrons with a certain spin projection can be efficiently extracted from S, wheareas electrons with the opposite spin can efficiently accumulate in S near the interface. This occurs due to the spin filtering of electrons in a tunneling process. We find conditions for most efficient extraction and accumulation of spin, and show that spin polarization of electrons near the interface can be made close to 100% in nondegenerate S at room temperature and certain bias voltages. The polarization of current in this regime is very low and decreases inversely proportionally to a total current J. At the same time, the spin density increases and spin penetration depth decreases with the current J. (C) 2004 American Institute of Physics.