Hydrogen above saturation at silicon vacancies: H-pair reservoirs and metastability sites - art. no. 105503

We propose that hydrogen-passivated multivacancies which appear to be fully saturated with H can actually capture additional H in electrically inactiv e sites. In silicon, first-principles total energy calculations show that s plitting an (m greater than or equal to 2) multivacancy into a mono- and an (m - 1) vacancy provides a low-strain pairing site for H, 0.4 eV per H low er than any known bulk pairing site. This monovacancy ejection mechanism is an excellent candidate for the H reservoir found both in crystalline and a morphous Si. A distinct H pairing on the fully saturated in vacancies, by f orming an internal surface Si-Si dimer, provides the final state of light-i nduced metastable degradation of hydrogenated amorphous silicon.