Mechanism of low-temperature (≤300 °C) crystallization and amorphization for the amorphous Si layer on the crystalline Si substrate by high-energy heavy-ion beam irradiation

By high-energy ({~}2.5-MeV) heavy-ion (⁷⁵{As}⁺$, $⁸⁴Kr⁺$, $131,132Xe⁺$, etc.) beam irradiation, the amorphous Si layers on the crystalline Si substrates formed by low-energy ({~}100-keV) ion implantation or by chemical-vapor deposition could be crystallized epitaxially at very low substrate temperatures (120--300 ^∘{}C, in the 2.5-MeV ⁷⁵As⁺ irradiation case), far below the ordinary solid-phase ({~}600 ^∘{}C) or liquid-phase ({~}1400 ^∘{}C) epitaxial growth temperatures. Layer-by-layer amorphization of amorphous Si layers on the crystalline Si substrates also occurred at low temperatures ({≤}120 ^∘{}C, in the 2.5-MeV ⁷⁵As⁺ irradiation case). The author elucidates the low-temperature (120--300 ^∘{}C) crystallization mechanism and the low-temperature ({≤}120 ^∘{}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.