Comparison of spin photocurrent in devices based on in-plane or out-of-plane magnetized CoFeB spin detectors

We have measured a helicity-dependent photocurrent at zero external magnetic field in a device based on a semiconductor quantum well embedded in a p-in junction. The device is excited under vertical incidence with circularly polarized light. The spin filtering effect is evidenced in the temperature range 77-300 K owing to a CoFeB/MgO spin filter with out-of-plane magnetization in remanence. The helicity-dependent photocurrent is explored as a function of the temperature and bias. These characteristics are compared with those of a spin photocurrent device with in-plane magnetized CoFeB/MgO spin filter, excited under oblique incidence with circularly polarized light. In contrast to the in-plane spin filter device, the circularly polarized light asymmetry of the photocurrent in the out-of-plane device depends weakly on the external bias. The two devices are sensitive to the spin filtering of either the in-plane (S x) or out-of-plane (S z) photogenerated electron spin in the semiconductor quantum well. The helicity-dependent photocurrent results can be explained by the Dyakonov-Perel electron spin-relaxation mechanism. Our study reveals the giant spin relaxation anisotropy in III-V zinc-blende quantum wells in the presence of a vertical electric field.