Spin detection and injection using ferromagnetic metal and semiconductor hybrid structure

We investigated spin-dependent transport properties from a viewpoint of spin detection and injection using a ferromagnetic metal/insulator (Al₂O₃)/semiconductor tunnel junction with homogeneous and flat interfaces. For spin detection from the semiconductor, spin-polarized electrons were excited in the GaAs layer by circularly polarized light and injected into the permalloy layer. The energy dependence of the observed helicity asymmetry of the photo-induced current shows the absence of the spin-dependent tunneling. The result suggests importance of controlling the electron lifetime to obtain the spin-dependent tunneling. For spin injection into a semiconductor, we prepared Co/Al₂O₃/AlGaAs/GaAs/AlGaAs light emitting diode (LED) structure with ferromagnetic electrode. The electro-luminescence from the LED depends on the magnetization direction of the ferromagnetic electrode at room temperature. This fact shows that a spin-injection from the ferromagnetic metal to the semiconductor is achieved. The spin polarization due to the spin-injection current is estimated to be the order of 1%.