Epitaxy and Nucleation in Cu and Ag Doped Amorphous Si

Abstract

AbstractThe competition between solid phase epitaxy and random nucleation during thermal annealing of amorphous Si implanted with the fast diffusers Cu and Ag has been studied. For low concentrations of these impurities, solid phase epitaxy proceeds with small deviations from the intrinsic rate and with the impurity remaining in the shrinking amorphous layer. At a critical metal concentration in the amorphous layer of ∼ 0.12 at.% rapid random nucleation occurs, halting epitaxy and transforming the remaining amorphous material to polycrystalline Si via grain growth. The nucleation rate is at least 8 orders of magnitude greater than the intrinsic homogeneous rate. At higher Cu concentrations nucleation is observed below the temperature needed for epitaxy (400°C). This nucleation, clearly caused by the presence of Cu or Ag in the layer, may be induced by the impurities exceeding the absolute stability concentration and starting to phase separate, leading to enhanced crystal Si nucleation in the metal rich regions.