Electronic transport at grain boundaries in silicon

Abstract

An experimental investigation is reported on carrier transport across isolated grain boundaries in large-grain cast silicon material. Continuous interface-state densities in the (${10}^{15}$-${10}^{16}$)-${\mathrm{m}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$ range are measured for the lower part of the silicon energy gap. The grain-boundary diffusion potentials for this material are shown in some cases to vary appreciably over a single grain-boundary plane; this is thought to be due to a nonuniform spatial distribution of interface charge at the grain boundaries. Numerical calculations by finite-element methods, of the quasi-Fermi-potentials in the vicinity of the grain boundary, suggest that the supply of majority carriers by diffusion to this interface may be the limiting factor controlling their transport. The experiments have consequently been interpreted according to the diffusion model rather than the customary thermionic-emission model of majority-carrier transport across grain boundaries.