Determination of Gallium Concentration in Silicon from Low-Temperature Photoluminescence Analysis

Increasing the understanding of the electronic properties of gallium (Ga) in silicon (Si) used nowadays to manufacture p-type Si solar cells is of key technological importance. In this contribution, the results of the effect of Ga concentration on the low-temperature photoluminescence (PL) spectra in crystalline Si are reported. The Ga-doped Si samples studied have negligible boron concentrations, which can complicate spectral analysis of the bound exciton (BE) lines. The split Ga BE ground state at T = 10 K is analyzed and the PL intensity ratios for the BE to free exciton peaks are compared. By comparing these to known Ga concentrations, derived from capacitance–voltage measurements, an all-optical (PL) calibration curve for the quantification of Ga concentration in Si is established. The effects of both temperature and excitation power on the PL intensity ratios are also studied. By combining the temperature-induced changes in the PL intensity ratios with the calibration curve at 10 K, a calibration function has been determined. It is found that the decay rates of the PL intensity ratios as a function of excitation power are independent of the chosen (split) BE peak. The major benefits of this method and its limitations are discussed.