THEORY OF NICKEL AND NICKEL-HYDROGEN COMPLEXES IN SILICON

Spin-polarized local density functional cluster calculations are carri ed out on substitutional Ni and Ni-H-2 complexes. We find that Ni- und ergoes a Jahn-Teller distortion along [100] with Ni moving slightly al ong the cube axis. The distorted state gives b(1), b(2), and a(1) leve ls in ascending order of energies within the gap in agreement with exp eriment. Several candidate NiH2 defects are investigated: the lowest e nergy 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.