Local vibrational modes of interstitial boron-interstitial oxygen complex in silicon

In the present work we report local vibrational mode (LVM) related absorption lines which are assigned to the complex incorporating interstitial boron and interstitial oxygen atoms (BiOi), a possible precursor of the center responsible for light induced degradation (LID) in solar cells produced from boron-doped oxygen-rich silicon. Fourier transform infrared absorption (IR) spectroscopy was used for detection and analysis of absorption lines due to defects which were created in boron-doped Czochralski-grown Si samples by irradiation with 6 or 10 MeV electrons at room temperature. Changes in the IR absorption spectra upon isochronal annealing of the irradiated samples in the temperature range 75-225 oC have also been monitored. A set of previously unreported LVM lines with the same formation and elimination behavior has been studied. The most intense lines of the set are found to be at 991, 721 and 551 cm-1. On the basis of an analysis of changes in intensity of the lines with the concentrations of impurities in the silicon and on the similarity of their annealing features with those for the DLTS signal due to the BiOi center it is argued that the lines are related to the LVMs of this defect. The positions of the lines have been compared with the previously reported LVMs derived from ab initio modeling calculations for different configurations of the BiOi complex. A configuration having calculated LVMs close to those determined experimentally has been found and the origins of the modes are discussed.