  The backscattering process of injected electrons on exchange-splitted levels
of quantum well (QW) in ferromagnetic metal / insulator / semiconductor
heterostructure is studied. It is found that, if one of the exchange-splitted
levels lies in the top region of the QW and the energy of injected electrons is
close to the energy of localized electron on this level, the backward
scattering becomes dependent on spins of injected electrons. Accumulation of
backscattered electrons in the QW leads to considerable reduction of the
current depended on its spin orientation. The spin polarization increases with
growth of the applied electric field and the storage time of electrons in the
QW. High values of the spin polarization can be achieved at room temperature.
In this way, the QW with exchange-splitted levels in ferromagnetic metal /
insulator / semiconductor heterostructure can be used as effective spin filter.
