Interactions of Hydrogen Atoms with Acceptor-dioxygen Complexes in Czochralski-grown Silicon

It is debated in the silicon PV community whether or not the presence of hydrogen is essential for the permanent suppression (“regeneration”) of the recombination activity of the boron-oxygen (BO) defect, which is responsible for light-induced degradation (LID) of solar cells produced from B-doped oxygen-rich silicon. The BO-LID defect has been identified as a BsO2 complex. Recently this complex has been shown to be a defect with negative-U properties. This study focuses on the interactions of hydrogen with the BsO2 defect to elucidate the BO-LID regeneration mechanism. With the use of junction spectroscopy techniques, the changes in concentration of the BsO2 donor state in diodes which were fabricated on Czochralski-grown (Cz) B-doped Si and subjected to hydrogenation and subsequent heat-treatments have been monitored. It is found that annealing of the hydrogenated Cz-Si:B diodes in the temperature range 398-448 K under the application of reverse bias, (RBA), resulted in nearly total disappearance of the BsO2 defect. It is argued that electrically neutral BsO2-H complexes have been formed upon the RBA treatments. According to ab-initio calculations, the binding energy of H+ to BsO2- exceeds that of H+ to Bs- by at least 0.1 eV, and the resulting BsO2-H complexes are electrically inactive.