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 that a broad emission band is observable at room temperature in the vicinity of the carbon-related C-line detected at cryogenic temperatures in electron-irradiated Si. Its spectral shape is different from similar shapes of the bands due to dislocations, oxygen precipitates, and thermal donors. The band is annealed out at 450 °C and its intensity ratio to the band-edge emission has a positive correlation with carbon concentration in the same manner as the C-line. We deduce that the band has a very similar origin to the C-line and discuss the possibility of carbon quantification by using the ratio as an index.

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.

We demonstrated the effectiveness of photoluminescence (PL) measurement at liquid N temperature after electron irradiation for the determination of the C concentration in P-doped n-type Czochralski-grown Si crystals. The disappearance of P-related lines simplifies the spectral analysis at 77 K, enabling us to estimate the C concentration from the G-line intensity ratio regardless of the difference in P concentration. The C concentration estimated by PL measurement at 77 K was in good agreement with those by measurement PL at 4.2 K and IR absorption. Unsusceptibility to the concentration of dopant impurities is a practical advantage of the PL measurement at 77 K over that at 4.2 K.

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