Photoluminescence Spectra of Moderately Doped, Compensated Silicon Si:P,B at 79–300 K

Photoluminescence (PL) spectra from moderately doped, compensated silicon with boron and phosphorus concentrations on the order of 10
¹⁶
- 10
¹⁷
cm
^{- 3}
, which is representative of the low-cost upgraded metallurgical grade silicon potentially used for photovoltaics, are presented and explained. At 79 K, the captured PL spectra from the compensated silicon reveal the presence of the following radiative recombination channels in the material: band-to-band recombination, recombination through a single neutral dopant (phosphorus or boron), and recombination from the neutral donors (phosphorus) to the neutral acceptors (boron), i.e., the D°-A° pair recombination. The D°-A° pair luminescence peaks are found to appear as rather broad in the measured PL spectra from compensated silicon at 79 K. The relative PL intensity of the broad dopant features is shown to increase with increasing dopant concentrations. The dopant-related luminescence of the compensated silicon demonstrates strong excitation dependence, as a result of the D°-A° recombination channel in compensated silicon. The dopant features become increasingly suppressed at higher excitations due to the increasing dominance of the band-to-band recombination channel. With increasing temperature, the dopant-related luminescence features diminish and become undistinguishable at around 200 K, due to the increased ionization of dopants and the broadening of the band-to-band recombination peaks at higher temperatures.