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 ori entation of p-GaAs. We have measured the phase-sensitive current modul ation which corresponds to the polarization modulation of the excitati on 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 spi n-dependent tunneling where the photoexcited electrons in the conducti on band of the GaAs enter into the unoccupied s,p-states of the ferrom agnet.