VOn (n >= 3) defects in irradiated and heat-treated silicon

Local vibrational mode (LVM) spectroscopy has been used to study the evolution of vacancy-oxygen-related defects (VOn) in the temperature range 300-700 degrees C in carbon-lean Cz-Si samples irradiated with MeV electrons or neutrons. New experimental data confirming an attribution of the absorption bands at 910, 976 and 1105 cm(-1) to the VO3 complex are obtained. In particular, a correlated generation of VO3 and the oxygen trimer is observed upon irradiation of CzSi crystals in the temperature range 300-400 degrees C. Strong evidence for the assignment of the bands at 991 and 1014 cm(-1) to a VO4 defect is presented. The lines are found to develop very efficiently in the VO2 containing materials enriched with the oxygen dimer. In such materials the formation of VO4 is enhanced due to occurrence of the reaction O-2i+VO2 double right arrow VO4. Annealing of the VO3 and VO4 defects at T >= 550C degrees C is found to result in the appearance of new defects giving rise to a number of O-related LVM bands in the range 990-1110 cm(-1). These bands are suggested to axise from VO5 and/or VO6 defects. Similar bands also appear upon the annihilation of oxygen-related thermal double donors at 650 degrees C in Cz-Si crystals pre-annealed at 450 degrees C.