Electron-irradiation-induced defects in Si-Ge alloys

We have studied the defects introduced by electron irradiation in n-doped Si-Ge alloys. Capacitance techniques were used to characterize the defects. Four deep levels are detected, labeled S1 to S4. Only the two main defects, S3 and S4, have been studied, the other ones having low concentration. Their associated energy levels lie at ${\mathit{E}}_{\mathit{c}}$-0.32 and ${\mathit{E}}_{\mathit{c}}$-0.49 eV with capture cross sections equal to 6×${10}^{\mathrm{-}16}$ and 2×${10}^{\mathrm{-}15}$ ${\mathrm{cm}}^2$, respectively. These two defects have a donor character. The study of their introduction rate versus the fluence indicates that they are not primary intrinsic defects but complexes. The variation of the S4 concentration versus the energy of irradiation shows that the threshold energy is 31±2 eV. Finally, a comparison with electron-irradiation-induced defects in silicon and germanium is made.