Silicon amorphization responses by combined irradiations with MeV ion beams and ultrashort laser pulses

Abstract

This work demonstrates a significant synergistic effect between MeV ion implantation and femtosecond laser irradiation in silicon amorphization. The achievable amorphization depth and the range of laser fluencies leading to amorphization is increased for implanted samples in comparison to pristine silicon. In Si(100) samples, prior to femtosecond laser irradiation (800 nm and 120 fs, or 1030 nm and 180 fs) ion-induced defects are produced with protons (0.6, 1 and 2 MeV) or Si-ions (2 MeV) at varying ion-irradiation fluences. Then, the investigated defects densities before laser irradiation range from low levels to levels approaching ion-induced amorphization (defects per atom, dpa, from 10–9 to 0.1). The optimal pre-conditioning for subsequent femtosecond laser-induced amorphization is found at a moderate defect density level, dpa =10–5. Additionally, it is shown that the achievable spatial resolution of the synergistic material amorphization is determined by the high resolution of the focused ion irradiation, suggesting a potential pathway for high-resolution patterning based on laser-assisted techniques. However, at high defect densities (dpa ≈ 0.1), the synergistic effect diminishes, and femtosecond laser irradiation instead reduces disorder, indicating a defect-annealing effect rather than further amorphization.