We report on the anomalous excitation-power dependence of the band-edge emission in Si after 2 MeV electron irradiation. It is well-established that the dependence of the emission intensity I on the excitation power L is generally follows the power law, I ∝ Ln with the exponent n between 1 and 2. However, the exponent n increases after the electron irradiation and becomes larger than 2 at temperatures from 60 to 150 K in all the measured samples. The present dependence can be explained by a simple model: the radiation-induced defects act as dominant recombination centers in the low excitation-power range, but their activity becomes saturated in the high excitation-power range.

We investigated the detection limit of carbon in Si for the photoluminescence (PL) method after electron irradiation. The detection limit was obtained from the intensity ratio of the G-line to the free exciton line with the G-line intensity twice as high as the noise level and was estimated at 4 × 1013 cm−3 under the measurement condition in accordance with the standard [JIS H0615] for quantification of donor and acceptor impurities in Si at 4.2 K. We showed that the limit is extendable down to 2 × 1013 cm−3 by optimizing the excitation power and sample temperature.

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We determined the entire spectral shape of a broad band around 0.8 eV, previously termed the C08-band, which was observed commonly in Si by room-temperature photoluminescence after electron irradiation. The band has a peak at 0.77 ± 0.01 eV with long tails on both sides. We identified that the C08-band has the same origin as the C-line and occurs as a result of the recombination between a free electron and a hole bound by the deep trap due to the interstitial C and O defects (CiOi). The long tails were explained by the superposition of phonon sidebands.

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