Donor-acceptor pair luminescence in compensated Si for solar cells

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.