Spin-dependent transport of carriers in semiconductors

This article reviews spin-dependent transport of carriers in homogenous three-dimensional and two-dimensional semiconductors. We begin with a discussion of optical orientation of electron spins, which allows both the creation and detection of spin-polarized carriers in semiconductors. Then we review non-equilibrium spin flow including spin drift and diffusion caused by electric fields and concentration gradients. A controlled spin precession is possible both in external magnetic fields and in effective magnetic fields due to a broken inversion symmetry. Although the Coulomb interaction does not couple to the spin degree of freedom, it affects the spin-dependent transport via the spin Coulomb drag. In gyrotropic media, the optical creation of spin-oriented electrons gives rise to spin photocurrents, which reverse their direction when the radiation helicity is changed from left-handed to right-handed. The reverse process is possible, too, i.e., an electric current in a gyrotropic medium gives rise to a spin polarization in the bulk of the sample.