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.