Vacancy-impurity pairs in relaxed Si1−xGex layers studied by positron annihilation spectroscopy

Positron annihilation spectroscopy was applied to study relaxed P-doped n-type and undoped Si1−xGex layers with x up to 0.30. The as-grown SiGe layers were found to be defect free and annihilation parameters in a random SiGe alloy could be represented as superpositions of annihilations in bulk Si and Ge. A 2 MeV proton irradiation with a 1.6 1015 cm−2 fluence was used to produce saturated positron trapping in monovacancy related defects in the n-type layers. The defects were identified as V-P pairs, the E center. The distribution of Si and Ge atoms surrounding the E center was the same as in the host lattice. The process leading to the formation of V-P pairs therefore does not seem to have a significant preference for either Si or Ge atoms. In undoped Si1−xGex we find that a similar irradiation produces a low concentration of divacancies or larger vacancy defects and found no evidence of monovacancies surrounded by several Ge atoms.