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Shown is a piece of polycrystalline Si. |
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The colors code the minority carrier diffusion length
which is a function of the concentration of certain impurities; in this case probably iron (in the ppb region). Light
colors (yellow, red) denote large diffusion length and low impurity concentrations, dark colors the opposite. The scale gives precise numbers.
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The grain boundaries are essentially black, because carriers will recombine there; life time and thus
diffusion length is small.
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Around the grain boundaries is a red/yellow zone, showing increased diffusion length as compared to the
interior of a grain. This corresponds to a decreased impurity concentration, because the iron in the neighborhood of a grain
boundary has diffused to the grain boundary where it is trapped. Knowing the thermal history of the sample allows an estimate
of the diffusion coefficient of iron in Si. |
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© H. Föll (Defects - Script)
3.3.1 Determination of Diffusion Profiles 
With frame