IMPURITY TRAPPING AND GETTERING IN AMORPHOUS-SILICON

Palladium atoms have been gettered from the bulk of an amorphous Si (alpha-Si) layer to an ion-implanted surface region. The 2.2-mu-m-thick alpha-Si layers, formed by MeV Si implantation, were implanted with 500 keV Pd and then annealed at 500-degrees-C. This produces a complete redistribution of Pd within the layer and relaxation or substantial defect annihilation in the alpha-Si. Subsequently, defects were introduced into the surface region (approximately 4000 angstrom) by 200 keV Si implantation at various doses. After low-temperature diffusion at 250-degrees-C, Pd atoms are gettered in the Si-implanted region. At low Si fluences, Pd decorates the Gaussian depth distribution of the ion-induced damage, while at higher a saturation is reached in the gettering profile. The ion damage is calculated to saturate when 2% of the target Si atoms are displaced by atomic recoils. Below saturation, the displacement of two Si atoms is calculated to produce one Pd trapping site.