Transport properties of ferromagnet/insulator/semiconductor tunnel junctions

Spin-dependent transport of the photoexcited electrons in the semiconductor (p-GaAs)/insulator $({\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{)/}\mathrm{ferromagnetic}$ metal (permalloy) junctions was investigated. As samples, homogeneous tunneling junctions were prepared on the flat and As-defect-free GaAs(111)B homoepitaxial surface by in situ oxidation of the Al layer and successive metallization by permalloy deposition. Spin-polarized electrons were excited in the GaAs by circularly polarized light and injected into the permalloy layer. Since the permalloy has almost zero magnetic circular dichroism at the vicinity of the band gap energy of GaAs, we can detect spin-dependent current exclusively. As a result, the energy dependence of the observed helicity asymmetry (1.44–3.05 eV) of the photoinduced current shows the absence of the spin-dependent tunneling in the sample. The importance of controlling the electron lifetime to obtain the spin-dependent tunneling was discussed.