Interface and surface segregation of germanium in the SiGe semiconductor

The concentration and distribution of germanium in the silicon crystal or SiGe alloy can play critical roles in affecting the performance of prepared semiconductor devices. We quantitatively investigate the segregation behavior of germanium in silicon and SiGe semiconductor based on molecular dynamics simulation using the Stillinger-Weber (SW) and Tersoff empirical potentials. The value predicted by the SW potential is 0.35 which agrees with some reported experimental results. Both potentials predict that the Ge equilibrium segregation coefficient at the solid/liquid interface of silicon is smaller than one. The germanium atoms tend to segregate to the surface in the SiGe nano structures in order to lower the surface energy. We define the surface segregation coefficient Ks to quantitively describe this behavior. It is found that Ks decreases with the increase of total germanium atomic fraction in the liquid slab. The size dependence of the surface segregation coefficient in the nanodroplet is studied and it scales with 1/R3 linearly. The germanium distribution in the SiGe solid slab and nanoparticle is largely affected by the Ge distribution in the liquid slab and nanodroplet before crystallization.