Electrically active defect centres related to sodium in silicon have been examined with deep level transient spectroscopy, and their recombination potential analysed with the microwave photoconductive decay technique. In order to investigate the entire silicon band gap for defect centres, both p-type (B-doped) and n-type (P-doped) float zone monocrystalline silicon samples were ion implanted with sodium. Three Na-related levels were identified in the upper half of the band gap at EC − 0.094 eV, EC − 0.119 eV and EC − 0.139 eV in implanted n-type silicon. In implanted p-type silicon three Na-related levels were identified at EV + 0.088, EV + 0.270 eV and EV + 0.139 eV. The capture cross sections of all levels were in the range 2–5 × 10−15 cm2, with an exception for the level at EV + 0.270 eV that was found to have a capture cross section of 4 × 10−14 cm2. Implantations of sodium lead to a significant drop in minority carrier lifetime of both n-type and p-type silicon. This degradation was substantially higher in p-type silicon. The observed recombination activity can be compared to that of nickel and manganese.
Semiconductor Science and Technology, 2013, Vol 28, Issue 10