Measurements of the dark electrical conductivity ${\mathrm{\sigma }}_{\mathit{D}}$ performed on hydrogenated polycrystalline silicon (poly-Si:H) reveal a cooling-rate dependent metastable increase of ${\mathrm{\sigma }}_{\mathit{D}}$ below 268 K. This nonequilibrium state relaxes slowly and the time to reach equilibrium is thermally activated with ${\mathit{E}}_{\mathrm{\tau }}$≃0.74 eV. Since thermal quenching does not affect unhydrogenated specimens, the observed metastable changes are clearly due to the formation and dissociation of an electrically active hydrogen complex. We propose that this complex consists of an isolated H atom at the bond-center site of a prestrained Si-Si bond at a grain boundary.

• Received 17 March 1994

DOI:https://doi.org/10.1103/PhysRevLett.72.3393