Vacancy-impurity pairs in n-type Si1-xGexSi1-xGex studied by positron spectroscopy

Positron annihilation spectroscopy was applied to study relaxed P-doped n-type Si1-xGexSi1-xGex layers with Ge concentrations up to 30%. As-grown SiGe layers were defect-free and annihilations are superpositions from bulk Si and Ge. Proton irradiation at 2 MeV energy with a 1.6×1015cm-2 fluence was used to produce saturated positron trapping in monovacancy related defects. The defects were identified as V–P pairs, the E-center. The distribution of Si and Ge atoms surrounding the E-center is the same as in the host lattice. The vacancy migration process leading to the formation of V–P pairs therefore does not seem to have a preference for either Si or Ge atoms.