Spin diffusion in doped semiconductors

Summary form only given. The motion and persistence of inhomogeneous electronic distributions are central to the electronic technologies based on semiconductors. Recently a broader category of possible disturbances, namely those involving inhomogeneous spin distributions in doped semiconductors, have been shown via ultrafast optical experiments to exhibit long lifetimes and anomalously high diffusion rates. This behavior indicates the potential of a new electronic technology relying on spin. These spin distributions are also of fundamental interest, for they are long-lived and very extended nonequilibrium coherent states. We have explored the properties of doped and undoped semiconductors which are spin-polarized or unpolarized in equilibrium. We find dramatic influences on the mobility and diffusion of spin packets due to the requirement of local charge balance. In an undoped semiconductor an excess of electrons must be balanced by an excess of less mobile holes. A spin packet in an n-doped semiconductor, however, can consist of a depletion of one spin species in the conduction band and an enhancement of the other. This packet´s transport properties are determined by those of the conduction band. In a spin-polarized semiconductor only spin packets polarized antiparallel to the equilibrium carrier spin polarization are single-band disturbances. For a spin-polarized n-doped semiconductor these spin packets should move orders of magnitude faster than those polarized antiparallel to the equilibrium carrier spin polarization.