Molecular dynamics simulation of ion-beam-amorphization of Si, Ge and GaAs J. Nord * , K. Nordlund, J. Keinonen Accelerator Laboratory, University of Helsinki, P.O. Box 43, FIN-00014 Helsinki, Finland Abstract We use molecular dynamics simulations to study ion-irradiation-induced amorphization in Si, Ge and GaAs using several different interatomic force models. We find that the coordination number is higher, and the average bond length longer, for the irradiated amorphous structures than for the molten ones in Si and Ge. For amorphous GaAs, we suggest that longer Ga–Ga bonds, also present in pure Ga, are produced during the irradiation. In Si the amorphization is found to proceed via growth of amorphous regions, and low energy recoils are found to induce athermal recrys- tallization during irradiation. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 64.70.Kb; 61.43.Dq; 61.72.Cc; 61.82.Fk Keywords: Amorphization; Irradiation; Defects; Semiconductors 1. Introduction Ion implantation of semiconductors often leads to amorphization of the material. Although the mechanisms leading to amorphization have been intensively studied [1–13], they remain subject to debate even in the most common semiconductor materials, such as Si. Early models tried to de- scribe the amorphization by either a direct impact (heterogeneous) or pure defect accumulation (ho- mogeneous) model, while many recent models are mixtures of these two models [14]. It is not clear whether the structure of irradiated amorphous material corresponds to that produced by other means, such as quenching. Some experiments in- dicate that at least the density of amorphous Si (a-Si) produced by ion irradiation is the same or smaller than that of crystalline Si (c-Si) [15]. On the other hand, other experiments and computer simulations observe an a-Si phase denser than c-Si [16,17]. In this paper, we study the amorphization of Si, Ge and GaAs by amorphizing the material with self-recoils. We use two different interatomic force models for Si and Ge. For GaAs we found only one model capable of describing crystalline-to-amor- phous phase transitions. 2. Method To study the ion-irradiation-induced amorph- ization process, we amorphized simulation cells by successive energetic recoils. The structural Nuclear Instruments and Methods in Physics Research B 193 (2002) 294–298 www.elsevier.com/locate/nimb * Corresponding author. Tel.: +358-9-191-50013; fax: +358- 9-191-50042. E-mail address: janne.nord@helsinki.fi (J. Nord). 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(02)00794-2