# Denuded Zones along Grain Boundaries

| Shown is a piece of polycrystalline Si.
|  | 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.
|  |  | The grain boundaries are essentially black, because carriers will recombine there; life time and thus diffusion length is small.
|  |  | 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.

With frame

3.3.1 Determination of Diffusion Profiles

© H. Föll (Defects - Script)