Role of electron tunneling in spin filtering at ferromagnet/semiconductor interfaces

Spin-dependent electron transport between a semiconductor and a ferromagnetic metal has been studied by polarized photoexcitation. Using a band gap engineered Au/NiFe/GaAs/AlGaAs/n-GaAs structure we are able to precisely control the bias and temperature range under which tunneling processes occur. We find that electron spin filtering is only observed when tunneling processes are switched on, whereas when tunneling is suppressed, only magneto-optical dichroism effects contribute to the polarization dependent photocurrent.