Spin Current and Its Electrical Detection in Semiconductors

The idea of utilizing the electron spin in semiconductor devices leads to the growth of the field semiconductor spintronics. This may result in the development of novel electronic devices with advantages over conventional electronics. However, the basic requirements necessary in developing semiconductor spintronic devices are the efficient generation/injection of spins (or spin current) in/into a semiconductor such that they can be transported reliably, i.e., without spin relaxation, over reasonable distances and, finally, detection of them. Since in spintronic devices, the information is carried by the electron spin, an electrical means of detecting spin current in semiconductors is desirable for fully exploring the possibility of utilizing spin degree of freedom and for possible device applications. Here, I describe an experiment which detects the spin current electrically in semiconductors by investigating the effect of a longitudinal electric field on the spin-polarized electrons generated by a circularly polarized light. The experiment observes the effect as a pure anomalous Hall voltage resulting from non-equilibrium magnetization induced by the spin-carrier electrons accumulating at the transverse edges of the sample as a result of asymmetries in scattering for spin-up and spin-down electrons in the presence of spin-orbit interaction. The results are presented by discussing the dominant spin relaxation mechanisms in semiconductors, and in relation with the recent understanding in this area.