MECHANISM OF LOW-TEMPERATURE (LESS-THAN-OR-EQUAL-TO-300-DEGREES-C) CRYSTALLIZATION AND AMORPHIZATION FOR THE AMORPHOUS SI LAYER ON THE CRYSTALLINE SI SUBSTRATE BY HIGH-ENERGY HEAVY-ION BEAM IRRADIATION

By high-energy (approximately 2.5-MeV) heavy-ion (As-75+, Kr-84+, Xe-131 Xe-132+, etc.) beam irradiation, the amorphous Si layers on the crystalline Si substrates formed by low-energy (approximately 100-keV) ion implantation or by chemical-vapor deposition could be crystallized epitaxially at very low substrate temperatures (120-300-degrees-C, in the 2.5-MeV As-75+ irradiation case), far below the ordinary solid-phase (approximately 600-degrees-C) or liquid-phase (approximately 1400-degrees-C) epitaxial growth temperatures. Layer-by-layer amorphization of amorphous Si layers on the crystalline Si substrates also occurred at low temperatures (less-than-or-equal-to 120-degrees-C, in the 2.5-MeV As-75+ irradiation case). The author elucidates the low-temperature (120-300-degrees-C) crystallization mechanism and the low-temperature (less-than-or-equal-to 120-degrees-C) amorphization mechanism. The thermal diffusion of vacancies towards the amorphous layer, produced by nuclear scattering of incident heavy ions in the crystalline substrate, plays an important role in the low-temperature crystallization. High incident energies also contribute to the enhanced vacancy diffusion due to their large electronic scattering. Whether crystallization or amorphization occurs depends on the balance at the crystalline-amorphous interface, between the vacancy concentration supplied from the crystalline substrate toward the amorphous layer via thermal diffusion and the interstitial Si-atom concentration supplied from the amorphous layer toward the crystalline substrate via recoil by incident heavy ions.