Angular Dependence of the Spin Photocurrent in a Co−Fe−B/MgO/n−i−p GaAs Quantum-Well Structure

Abstract

We evidence at room temperature the detection of photogenerated spin currents by using a magnetic electrode without the need of an external magnetic field. The device is based on a semiconductor (Al,Ga)As/GaAs quantum well embedded in a p−i−n junction. The spin filtering is performed owing to a Co−Fe−B/MgO electrode with in-plane magnetization. We observe a helicity-dependent photocurrent when the device is excited under oblique incidence with circularly polarized light. The helicity-dependent photocurrent is explored as a function of the incident and azimuth angles of the incoming light wave vector with respect to the magnetization direction of the magnetic electrode. The results are interpreted as a consequence of the photogenerated average electron spin under oblique incidence in a quantum well governed by optical selection rules involving electron-heavy-hole and electron-light-hole transitions. A systematic study of the helicity asymmetry as a function of the photon energy and applied bias is performed. It demonstrates that this asymmetry is at its maximum close to the GaAs quantum well and (Al,Ga)As bulk optical transitions. The asymmetry can be controlled by an external bias on the structure. Finally, we show that this asymmetry decreases when the temperature increases.