Spin-dependent electron tunneling in ferromagnetic metal/insulator/semiconductor junctions using optical spin orientation

We examined the spin-dependent tunneling of photoexcited electrons in FM/Al2O3/p-GaAs (FM=Ni and Co) junctions by using the optical spin orientation of p-GaAs. We have measured the phase-sensitive current modulation which corresponds to the polarization modulation of the excitation light. The relative changes of conductance Delta G/G, with respect to the magnetization reversal of the ferromagnet, were found to be 0.3 and 0.8% for Ni and Co, respectively. From bias-dependence of Delta G/G, we assigned that the observed changes were responsible for the spin-dependent tunneling where the photoexcited electrons in the conduction band of the GaAs enter into the unoccupied s,p-states of the ferromagnet.