Light-induced Lifetime Degradation in Boron-doped Czochralski Silicon: Are Oxygen Dimers Involved?

Light-induced electron lifetime degradation in boron-doped Czochralski silicon was studied before and after a prolonged annealing at 350oC (up to 120 h) and 300oC (up to 8 weeks). Such a heat treatment is known to reduce significantly – by a factor of 3 or more - the concentration of oxygen dimers. The lifetime degradation observed in these samples was not however remarkably reduced; on the contrary, it was sometimes slightly increased. This result shows unambiguously that oxygen dimers - present in the material before illumination - do not participate in formation of the lifetime-degrading centres. This conclusion is in line with some other features of the degradation. The known proportionality of the centre density to the squared oxygen concentration and to the boron concentration can originate from BsO2 defects already present before illumination – in a concentration which depends on thermal history and, in particular, may slightly increase during above-mentioned prolonged annealing.