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We attempted the quantification of carbon concentration in Czochralski-grown Si crystals for solar cells by luminescence activation in the concentration range lower than the detection limit of IR absorption spectroscopy. A positive correlation was found between the relative intensity of the C-line and the substitutional carbon (Cs) concentration determined by IR absorption in the low 1015 cm−3 range. The detection limit was estimated to be approximately 5 × 1012 cm−3. We measured and compared the Cs concentrations in the wafers sliced from ingots grown under different conditions. The variations in Cs concentrations in the respective ingots were consistent with the segregation effect.

We demonstrate practical great advantages of the photoluminescence (PL) measurement at liquid N temperature after electron irradiation for quantifying low-level C in Si compared with the measurement at liquid He temperature. The broadening of the C-related C- and G-lines enabled us to detect the lines rapidly with high sensitivity by using the optimized low-dispersion spectroscopic apparatus. Positive correlations were found between their intensity ratios to the band-edge emission and the C concentration estimated by PL measurement at 4.2 K. The disappearance of dopant-impurity-related lines simplifies the recombination process, suggesting the improvement of quantification accuracy.

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