THEORY OF NICKEL AND NICKEL-HYDROGEN COMPLEXES IN SILICON

Spin-polarized local density functional cluster calculations are carried out on substitutional Ni and Ni-H-2 complexes. We find that Ni- undergoes a Jahn-Teller distortion along [100] with Ni moving slightly along the cube axis. The distorted state gives b(1), b(2), and a(1) levels in ascending order of energies within the gap in agreement with experiment. Several candidate NiH2 defects are investigated: the lowest energy structure consists of a substitutional Ni atom together with two H atoms at antibonding sites to two Si neighbors of Ni. This gives H related vibrational modes and a spin-polarized charge density close to those reported for Pt-H-2.