Amorphization mechanism and defect structures in ion-beam-amorphized Si, Ge, and GaAs

We are studying ion-irradiation-induced amorphization in Si, Ge, and GaAs using molecular-dynamics simulations. Although high-energy recoils produce defects and amorphous pockets, we show that low-energy recoils (about 5-10 eV) can lead to a significant component of the athermal recrystallization of preexisting damage. For typical experimental irradiation conditions this recrystallization is, however, not sufficient to fully recrystallize larger amorphous pockets, which grow and induce full amorphization. We also examine the coordination and topological defect structures in Si, Ge, and GaAs observed in the simulations, and find that these structures can explain some experimentally observed features found in amorphous semiconductors. For irradiated amorphous GaAs, we suggest that long (about 2.8 Angstrom) and weak Ga-Ga bonds, also present in pure Ga, are produced during irradiation.