Ag and Ag–Cu interactions in Si

Abstract

Noble metals are often used for contacts on Si. A considerable amount of research has been done on Cu- and Au-related defects, but much less is known about Ag. Silver is a common contaminant in metallic copper and the *Cu0 photoluminescence defect has been shown to contain one Ag atom. In this study, we predict the properties of isolated interstitial (Agi) and substitutional (Ags) silver. The calculated migration barrier of Agi is 0.53 eV, less than half the value extracted from the high-temperature solubility data. Agi has a donor level high in the gap and is in the positive charge state for most positions of the Fermi level. When interacting with a pre-existing vacancy, Agi becomes Ags with a gain in energy slightly higher than in the case of Cu but still less than the formation energy of the vacancy calculated at the same level of theory. The calculated donor and acceptor levels of Ags are close to the measured ones, and we predict a double-acceptor level that matches a Ag-related (but otherwise unidentified) level reported in the literature. The AgsCui pair is more stable than the CusAgi pair. Ags can trap several Cuis and form Ags1Cuin complexes (n = 1–4) that are similar to the Cus1Cuin ones. When needed, their calculated binding energies are corrected to account for a change of the charge state following the formation of the complex. This correction is Fermi level dependent. We tentatively assign the *Cu0 defect to Ags1Cui3 even though the single-donor level associated with *Cu0 does not match the calculated one.