Ga Implantation Induced Atomic Mixing in Crystalline and Amorphous Ge Isotope Multilayers

Self-atom mixing induced by Gallium (Ga) implantation in crystalline and amorphous germanium (Ge) is investigated using an isotopic multilayer structure of alternating 73 Ge and nat Ge layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and ion-beam induced depth-dependent mixing was determined by means of the secondary ion mass spectroscopy (SIMS). The position and form of the implanted Ga peak is very similar in the amorphous and crystalline Ge and can be reproduced accurately by SRIM simulations, whereas the ion-beam induced self-atom mixing strongly depends on the state of the Ge structure. The data from SIMS-measurements reveal a stronger mixing of the crystalline compared to amorphous structure. Molecular dynamics simulations suggest a higher mixing efficiency in the amorphous structure due to the lower thermal transport capacity. The kinetic energy of the implanted ions cause thermal spikes characterized by localized melted regions. Because of the lower thermal transport capacity of the amorphous structure the thermal spike lasts longer and leads to a higher mixing efficiency. The experimentally observed disparity in the ion-beam mixing efficiency of crystalline and amorphous Ge in comparison with the simulation indicates different mixing mechanisms.