Spin-polarized electron transport in ferromagnet/semiconductor hybrid structures (invited)

Two major problems in spin electronics remain to be solved: room temperatur e spin injection at a source and spin detection at a drain electrode. The l ateral size of magnetic contacts and the presence of a potential barrier at the interface are believed to have a key influence on the efficiency of bo th of these processes. We therefore aimed to clarify these issues by studyi ng spin-polarized transport across epitaxially grown single crystal Fe (001 )/GaAs nanoclusters and at the Schottky barrier formed at Ni80Fe20/GaAs int erfaces. We observed a negative contribution to the magnetoresistance of an ultrathin (2.5 ML) discontinuous epitaxial Fe film as occurs in tunnel mag netoresistance. This result suggests that spin transport via GaAs is possib le on the nanoscale. In the continuous NiFe/GaAs structures, circularly pol arized light was used to create a population of spin-polarized electrons in the GaAs substrate and spin-polarized electron transport across the interf ace at room temperature was detected as an electrical response associated w ith the field-dependent photocurrent. Surprisingly, highly efficient spin t ransmission is observed at room temperature, indicating that there is no si gnificant loss of spin polarization for electrons crossing the interface. T his result unambiguously demonstrates that spin detection is possible at ro om temperature in a continuous ferromagnet/semiconductor contact in the pre sence of the Schottky barrier. (C) 2001 American Institute of Physics.