Hydrogen-induced metastable changes in the electrical conductivity of polycrystalline silicon

Measurements of the dark electrical conductivity σD performed on hydrogenated polycrystalline silicon (poly-Si:H) reveal a cooling-rate dependent metastable increase of σD below 268 K. This nonequilibrium state relaxes slowly and the time to reach equilibrium is thermally activated with E_τ{}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.