Theory of Nickel and and Nickel - Hydrogen Complexes in SiliconR

Spin-polarized local density functional cluster calculations are carried out on substitutional Ni and Ni-H 2 complexes. We nd that Ni ? undergoes a Jahn-Teller distortion along h100i 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 NiH 2 defects are investigated: the lowest energy structure consists of a substitutional Ni atom together with two H atoms at anti-bonding 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 .