The effect of compound composition and strain on vacancies in Si/SiGe heterostructures

In this paper we study the effect of chemical environment and elastic strains, which can arise in layered heterostructures due to the lattice parameter mismatch, on the vacancy formation energy in random Si-Ge compounds. Ab initio calculations demonstrate a number of simple trends characterizing the vacancy formation energy dependence on vacancy charge, the number of Ge atoms in its neighbourhood and on the magnitude of elastic strains. The obtained parameters of vacancy- germanium interaction indicate, in particular, a tendency for preferential vacancy accumulation in SiGe region of Si/SiGe/Si layered structures, which is confirmed here by MonteCarlo simulation of high-temperature vacancy annealing and agrees well with recent experimental observations.