SPIN-DEPENDENT TRANSPORT AT SILICON GRAIN-BOUNDARIES

The transport of electronic carriers across grain boundaries in n- and p-type silicon has been measured as a function of magnetic field in the presence of a microwave field. The spin-dependent-transport (SDT) signal is observed to have a distinctively different character depending on whether the samples are illuminated with band-gap light or are in the dark. Despite the approximate symmetry of the dark I-V curves, the dark SDT signals, which are only observed for n-type boundaries, are asymmetric, displaying an increased impedance at the resonance condition for one current direction and a decrease for the other. With band-gap illumination, a symmetric SDT signal is seen for all samples which becomes quite large at high light intensities. The line shapes and g values seen for these resonances are similar to those attributed to Si dangling-bond-like defects. The dark SDT effect may be associated with a spin-flip k-vector change which must take place for conduction-band electrons that are thermionically emitted over the grain-boundary double depletion layer. The light-induced SDT effect is well modeled as a spin-dependent change of the light-generated minority carrier flux that modulates the trapped majority-carrier density at the grain-boundary plane.