Atomistic simulation of ion irradiation of semiconductor heterostructures

Recently the possibility to use ion beam mixing combined with suitable annealing has been suggested as a possible means to synthesize individual silicon quantum dots in a silica layer, with the possibility to function as single-electron transistors. For this to work, it is necessary to have a careful control of the ion beam mixing in Si/SiO2/Si heterostructures, as well as understand the nature of not only the composition, but also the chemical modification of the SiO2 layer by the mixing with Si. We describe here a procedure to synthesize Si/SiO2/Si heterostructures in molecular dynamics, with an energy minimization scheme to create strong and stable interfaces. The created heterostructures are irradiated at energies and fluences matching corresponding experiments. The results show a considerable degree of interface mixing, as expected. They also show some densification of the silica layer due to recoil implantation, and formation of a considerable number of coordination defects. Due to the strong covalent bonding in silicon and silica, the densification is not fully elastically relaxed even in the presence of a nearby surface.