Photoluminescence observation of donor pairs in silicon

The asymmetric broadening with a tail on the lower energy side and the peak shift to lower energies are observed in the luminescence band due to bound excitons in silicon crystals which contain phosphorus impurities below the critical concentration for semiconductor-metal transition (8 × 10¹⁶ -3 × 10¹⁸ cm^-3). These behaviors are understood in terms of an exciton bound to a donor pair in silicon.