Ab Initio Analysis of Point Defects in Plane-Stressed Si or Ge Crystals

Abstract

The effect of compressive and tensile plane-stress on the formation energy of vacancies (V) and self-interstitials (I) in Si or Ge crystals was studied with an ab initio approach for in-plane strains up to 5.0%. In both Si and Ge crystals, (i) generally, the formation energy of I decreased under tensile in-plane strain, while the formation energy of V decreased under compressive in-plane strain, (ii) compressive strain increases the stability region of V -2 in the band gap, while the strain does not shift significantly the stability region of I 0 and I +2 at the [110] dumbbell site. The dependence of the formation energy of I at the tetrahedral site on in-plane strain was different between Si and Ge. The other calculations showed that Young's modulus and Poisson's ratio of Si or Ge crystals are in good agreement with experimental results. Mechanical strength of a thin Si film, which is important for device applications, is also evaluated with an ab initio approach.