Ion-beam mixing in crystalline and amorphous germanium isotope multilayers

Gallium (Ga) implantation induced self-atom mixing in crystalline and amorphous germanium (Ge) is investigated utilizing isotopically controlled Ge multilayer structures grown by molecular beam epitaxy. The distribution of the Ga ions and the ion-beam induced depth-dependent mixing of the isotope structure was determined by means of secondary ion mass spectrometry. Whereas the distribution of Ga in the crystalline and amorphous Ge is very similar and accurately reproduced by computer simulations based on binary collision approximation (BCA), the ion-beam induced self-atom mixing is found to depend strongly on the state of the Ge structure. The experiments reveal stronger self-atom mixing in crystalline than in amorphous Ge. Atomistic simulations based on BCA reproduce the experimental results only when unphysically low Ge displacement energies are assumed. Analysis of the self-atom mixing induced by silicon implantation confirms the low displacement energy deduced within the BCA approach. This demonstrate...