Spin-polarized electron transport processes at the ferromagnet/semiconductor interface

Circularly polarized light was used to excite electrons with a spin polariz ation perpendicular to the film plane in ferromagnet/semiconductor hybrid s tructures. The Schottky characteristics at the interface were varied by usi ng NiFe, Co and Fe as the ferromagnet, The Schottky characteristics were cl early observed with NiFe and Co/GaAs, while almost ohmic I - V characterist ics were seen with Fe/GaAs, At negative bias a helicity-dependent photocurr ent, dependent upon the magnetization configuration of the him and the Scho ttky barrier height, was detected upon modulating the polarization from rig ht to left circular. For the magnetization along or perpendicular to the su rface normal, the helicity-dependent photocurrent I-n or I-o, respectively, was measured. The asymmetry P = (I-n - I-o)/(I-n + I-o) of the helicity-de pendent photocurrent decreases upon increasing the doping density of the Ga As substrates. P also decreases with photon energy h nu as found for the po larization of photoexcited electrons in GaAs, In NiFe/GaAs samples for h nu = 1.59 eV, P = 16% for n(+) = 10(23) m(-3) and P = -23% for p(-) = 10(25) m(-3) doped substrates, i.e. P is comparable in magnitude to the theoretica lly predicted spin polarization of 50% for the optically pumped conduction band in GaAs, The results provide unambiguous evidence of spin-polarized el ectron transport through the ferromagnet/semiconductor interface and show t hat the Schottky barrier height controls the spin-polarized electron curren t passing from the semiconductor to the ferromagnet, The asymmetry data ind icates that spin-polarized electrons are transmitted from the semiconductor to the ferromagnet with a high efficiency.