Current-Induced Spin Polarization in Nonmagnetic Semiconductors

The use of spontaneous electron spin polarization in nonmagnetic semiconductors avoids the transport challenges of electron spin injection from magnetic materials as well as packing constraints of small magnets in a dense array. Although the focus of rearch on the spontaneous spin polarization of electrical current has been on spin-orbit fields and their effects, in principle a moving electron gas can be unstable to forming spin-polarized distributions via carrier scattering processes that are independent of the carrier spin. The two required elements for such current-induced spin polarization without spin-orbit interactions are (1) the presence of built-in spatially-varying electric fields, either naturally forming (as in the Gunn effect) or extrinsic (as in a junction with spatially dependent doping) and (2) energy-dependent carrier scattering processes. As spin-orbit interactions are not required for this effect, it should occur in inversion-symmetric materials like silicon that lack zero-field spin splittings and materials like zinc oxide and gallium nitride that lack significant spin-orbit interactions.