HYDROGEN-INDUCED METASTABLE CHANGES IN THE ELECTRICAL-CONDUCTIVITY OFPOLYCRYSTALLINE SILICON

Measurements of the dark electrical conductiVitY sigma(D) performed on hydrogenated polycrystalline silicon (poly-Si:H) reveal a cooling-rat e dependent metastable increase of sigma(D) below 268 K. This nonequil ibrium state relaxes slowly and the time to reach equilibrium is therm ally activated with E(tau) congruent-to 0.74 eV. Since thermal quenchi ng does not affect unhydrogenated specimens, the observed metastable c hanges are clearly due to the formation and dissociation of an electri cally active hydrogen complex. We propose that this complex consists o f an isolated H atom at the bond-center site of a prestrained Si-Si bo nd at a grain boundary.