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The electrical activity of Ga impurities in a high concentration range in B and P highly compensated Si co-doped with Ga for photovoltaic applications has been investigated through the analysis of donor-acceptor pair luminescence. We have identified the fine structure due to the pair luminescence between P-donors and Ga-acceptors based on a comparison with a theoretical spectrum using their generally accepted ionization energies in low concentration ranges in uncompensated Si. The fine structure showed no dependence on dopant concentrations in the P and Ga concentration ranges from 7 × 1016 to 4 × 1017 cm-3 and from 5 × 1016 to 3 × 1017 cm-3, respectively, which leads us to suggest that both P and Ga impurities act as isolated donors and acceptors without noticeable reduction of ionization energies due to high doping. [ABSTRACT FROM AUTHOR]

A broad band with a fine structure on the higher energy side has been commonly observed in photoluminescence at 4.2 K from compensated Si for solar cells involving P donors and B acceptors on the order of 1016 cm-3. We calculated the theoretical spectrum of donor-acceptor (DA) pair luminescence from the density distribution of pairs as a function of the transition energy of respective pairs with separations ranging from 1.9 to 3.3 nm. A close agreement was obtained between the observed spectral structure and the theoretical curve using the generally accepted P donor and B acceptor ionization energies, where a systematic deviation was explained by the Van der Waals interaction between shallow P donors and B acceptors. This allows us to conclude that the band with the fine structure is due to the P-donor-B-acceptor pair recombination. This identification was confirmed by the observation of As-donor-B-acceptor pair luminescence in an As-doped sample. The present findings indicate that P and B impurities with concentrations on the order of 1016 cm-3 are unlikely to form complexes and that their ionization energies are not changed from those in the low concentration range. [ABSTRACT FROM AUTHOR]