Determination of low carbon concentration in Czochralski-grown Si crystals for solar cells by luminescence activation using electron irradiation

Abstract

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.

Origin of room-temperature photoluminescence around C-line in electron-irradiated Si and its applicability for quantification of carbon

“…Photoluminescence (PL) measurement after the introduction of carbon-related radiation damage [8][9][10][11][12][13][14][15][16][17] attracts considerable attention in detecting carbon in the concentration range lower than 5 × 10 15 cm −3 . It is well established that the highenergy-particle irradiation produces the interstitial C and interstitial O complex (C i -O i ) and the C i and substitutional C complex (C i -C s ), and that they are responsible for the PL emissions of the C-line at 0.789 eV and the G-line at 0.969 eV, respectively.…”

“…The carbon concentration varied from 2 × 10 14 to 4 × 10 16 cm −3 , which was determined either by the IR absorption method for the concentration range higher than 1 × 10 15 cm −3 or by secondary ion mass spectrometry (SIMS) for the range higher than 5 × 10 14 cm −3 , or estimated by PL measurement at 4.2 K for the range lower than 2 × 10 15 cm −3 . [12][13][14][15][16][17] We did not perform the IR or SIMS measurements and used the data given by the suppliers. The samples were irradiated with 2 MeV electrons with a fluence varying from 1 × 10 15 to 1 × 10 17 cm −2 at room temperature, where a fluence of 1 × 10 15 cm −2 was our most typical condition.…”

“…The details of the measurement condition at cryogenic temperatures have been reported elsewhere. 17,20) The temperature dependence of the PL spectra was examined in the range between 18 and 300 K by mounting a sample on a temperature-variable He gas closed-cycle cryostat, where the sample temperature was estimated from the half-width of the free-exciton line. 27) The spectral response of the spectroscopic apparatus was not calibrated in this study, since accurate calibration of the response is very difficult in the wavelength region of 1600-1700 nm because of the steep decrease in the responsivity, as shown in Fig.…”

“…We have observed that the intensities of the C-and G-lines are influenced greatly by the variations of the oxygen and dopant concentrations and the crystal growth conditions. [12][13][14][15][16][17][18][19]21,22) To suppress this effect, we chose 11 groups of samples. They were sliced from the same ingots or had nearly the same oxygen and dopant concentrations; the groups were identified by A-F, L-N, P, and S. Only the samples in group F were FZ wafers, and all the others were CZ wafers.…”

Free-to-bound emission from interstitial carbon and oxygen defects (CiOi) in electron-irradiated Si

“…9,10) An accurate lifetime control will be inevitable for high frequency power deices, where the precise management of small amount of residual C and O impurities is necessary. 11,12) The detection of C-and/or G-lines after electron irradiation has been also applied to quantify low-level C impurities: [13][14][15][16][17][18][19][20][21][22][23][24][25] the intensity ratios of these lines to the intrinsic line are used as indexes of the C concentration. This quantification method is being standardized as one of the most sensitive techniques for C in Si.…”