shows two pieces of polycrystalline Si with two different doping concentrations. However, the grain size shows in both subfigures nearly the same size distribution from a macroscopic point of view. From a microscopic point of view, for instance in a window $ 0.1 imes0.1$ microns, the area would include either 1 or a few grains. If the resistivity would be considered of this fictive area, the difference