ION-INDUCED CRYSTALLIZATION AND AMORPHIZATION AT CRYSTAL/AMORPHOUS INTERFACES OF SILICON

New empirical equations describing the rate of ion-induced crystallization at a Si crystal/amorphous interface have been developed. In our model, crystallization/amorphization at the interface arises from formation of hot spots and of knock-ons in the collision cascades. It is presumed that the hot spots induce amorphous-to-crystal transformation which lowers the free energy, similarly to heating to high temperatures, and that the bond rearrangement by a series of displacements by knock-ons and recombination to the original lattice point in collision cascades can lead to both crystal-to-amorphous and amorphous-to-crystal transformations. In both hot-spot and knock-on effects, the presence of di-vacancies under irradiation with ion beams is assumed to prohibit crystallization. The model can explain the experimental observation that the crystallization/amorphization rate is scaled by X = phi(1/2)exp(E/2kT), the product of the root of the flux and the inverse of root of the Boltzmann factor for the motion of the di-vacancies. Crystallization rate in the hot-spots derived assuming that an incident ion induces spontaneous crystallization within a characteristic volume along the track reveals that the radius is 10 atomic distances and the thickness of is about 0.3 monolayer for 1.5 MeV Xe ions. The calculated crystallization/amorphization rate fits to experimental results over a wide temperature range.