Atomistic modeling of the Ge composition dependence of solid phase epitaxial regrowth in SiGe alloys

摘要

The solid phase epitaxial regrowth (SPER) of SiGe alloys has been studied using atomistic simulation techniques. Molecular Dynamics (MD) simulations reproduce the recrystallization process of amorphous structures created in two different ways: introducing atoms at random positions according to the crystalline density and carefully relaxing the structure; and using a bond switching algorithm by means of ab initio. Activation energies are confronted, and the first method is validated as an efficient way to generate amorphous-crystalline structures suitable to study SPER processes. The MD extracted results show that the SPER rate does not vary monotonically with the Ge composition; instead, activation energies reveal a non-linear behaviour with the addition of Ge, due to the two-part behaviour of the SPER rate: SPER rate itself and a hypothesized extra strain due to the bond length difference. Since SPER is a thermally activated process, nudged elastic band calculations are carried out in order to extend the previous assumption. The energy barrier for an atom to attach to the crystalline phase is computed. The extracted values confirm the presence of the mentioned strain contribution required for an atom to recrystallize when it is not as the same type of the bulk.