Formation of oxygen dimers in silicon during electron-irradiation above 250°C

The oxygen dimer should be a first step in clustering of oxygen atoms in silicon. It has been suggested to play an important role in the formation kinetics of the thermal double oxygen donors formed during heat-treatments below 500 degrees C. Recently strong experimental indications of the dimer have been presented and infrared vibrational bands at about 1012 and 1060 cm(-1) have been assigned to an oxygen dimer. In this work a strong increase of these dimer related bands has been found in silicon crystals after electron (2 MeV) irradiation at elevated temperatures (250-300 degrees C). Additional related weaker vibrational bands also appear at about 556 and 690 cm(-1) at 10 K. Simultaneously vacancy-oxygen related defects as well as thermal double donors are formed. In carbon-rich material the dimer formation is strongly suppressed. Different models for dimer formation are discussed and a model where a silicon self-interstitial is trapped by a dioxygen-vacancy center is suggested.