It was proposed that H-passivated multivacancies which appeared to be fully saturated with H could capture additional H in electrically inactive sites. In Si, first-principles total energy calculations showed that splitting an (m ≥ 2) multivacancy into a mono- and an (m–1) vacancy provides a low-strain pairing site for H, 0.4eV per H lower than any known bulk pairing site. This monovacancy ejection mechanism was an excellent candidate for the H reservoir found both in crystalline and amorphous Si. A distinct H pairing on the fully saturated m vacancies, by forming an internal surface Si-Si dimer, provides the final state of light-induced metastable degradation of hydrogenated amorphous Si.

Hydrogen above Saturation at Silicon Vacancies - H-Pair Reservoirs and Metastability Sites. S.B.Zhang, H.M.Branz: Physical Review Letters, 2001, 87[10], 105503 (4pp)