We developed our own realization of photoconductance decay (PCD) lifetime measurement setup optimized for high carrier lifetime mono-Si ingots. The eddy current technique is used to sense the change of the photoconductance, while a 980nm long pulse laser is responsible for the excess charge carrier generation. The system is able to record lines-cans along the ingots. In the case of long carrier diffusion length, the shapes of the recorded transients are not exponential due to the recombination at the surface and due to the continuous in-diffusion of the carriers towards the bulk. It makes the proper extraction of bulk lifetime difficult by applying analytical formulas or simulations. Based on a phenomenological approach we suggest a simple empirical formula to fit the recorded photoconductance decay curves. The exponential decay component of the fitting function is associated with carrier lifetime. It is shown, that the extracted carrier lifetime is sensitive to metallic contamination in the sample, additionally, the extracted curve is independent of the surface conditions of the sample. Thus, this method is fast, simple and reliable, so applicable in industrial quality control protocols.
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