Radiation-induced defects in Czochralski-grown silicon containing carbon and germanium

Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (CiOi) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [Cs] up to 1 × 1017 cm−3 and Ge concentrations [Ge] up to 1 × 1020 cm−3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [Cs] around 2 × 1017 cm−3 the production rate of VO defects is getting larger by ~40% in Cz–Si:Ge at Ge concentrations around 1 × 1019 cm−3 and then at [Ge] ≈ 2 × 1020 cm−3 this enlargement drops to ~13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of CiOi complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm−1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes.