GRAIN-BOUNDARY MEDIATED AMORPHIZATION IN SILICON DURING ION IRRADIATION

Amorphous Si is nucleated heterogeneously at grain boundaries during irradiation of polycrystalline Si thin films by 1.5 MeV Xe+ ions for temperatures of 150-225°C. Moreover, the heterogeneous nucleation kinetics of amorphous Si are strongly dependent on grain boundary structure. Following formation at grain boundaries, the amorphous Si layer grows at a rate comparable to that previously observed at a pre-existing planar amorphous-crystal interface. As amorphization proceeds, a decrease in average grain size and a marked change in the grain size distribution results. We suggest a simple atomistic model for amorphous phase formation in Si in which the nucleation kinetics are dependent on the point defect-grain boundary interactions.