D. J. Backlund

Cobalt-related defects in silicon

Transition metals from the 3d series are unavoidable and unwanted contaminants in Si-based devices. Cobalt is one of the most poorly understood impurities with incomplete experimental information and few theoretical studies. In this contribution, the properties of interstitial cobalt (Coi) in Si and its interactions with the vacancy, self-interstitial, hydrogen, and substitutional boron are calculated using the first-principles tools. The stable configurations, gap levels, and binding energies are predicted. The activation energy for diffusing Coi is calculated with the nudged-elastic-band method and found to be slightly lower than that of interstitial copper and nickel. The binding energies and gap levels of the substitutional cobalt (Cos) and of the {Cos,H} and {Cos,H,H} complexes are close to the experimental data. The properties of the cobalt-boron pair are calculated.

Ti-H and Ni-H interactions in Si: first principles theory

Hydrogen is commonly used to remove (or at least reduce) the electrical activity of numerous defects and impurities in Si. Although hydrogenation works quite well for many defects, it has generally been unsuccessful with transition metal (TM) impurities. A number of {TM,Hn} complexes have been detected using optical or electrical techniques. Even though the gap levels of the isolated TM shift upon hydrogenation, many {TM,Hn} complexes remain electrically active. The nature of the complexes responsible for specific DLTS lines is generally not known, and the number of H interstitials in a given complex is assumed. We have performed systematic first-principles calculations involving Ti-H and Ni-H interactions in Si, assuming both interstitial and substitutional sites for the TM. The equilibrium configurations, binding energies, and approximate gap levels of all the {Ti,Hn} and {Ni,Hn} complexes are calculated.