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,H_n} complexes have been detected using optical or electrical techniques. Even though the gap levels of the isolated TM shift upon hydrogenation, many {TM,H_n} 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,H_n} and {Ni,H_n} complexes are calculated.