Electrical Resistivity of Doped Films

It is fairly obvious that this phenomena must be related to the fact that the poly is made up of many small grains with their attendent grain boundaries. Each grain is a single crystal and should behave as the epi films do. Therefore, the cause of the increased resistivity must involve the grain boundaries. 

Undoubtedly, both explanations play some role, since each has some experimental verification to support it. It will depend on the type of dopant, the extent of dopant, and grain size. As noted earlier in Chapter 2, poly grains will grow larger when the film is doped, as well as annealed at a high temperature for a reasonable length of time. 

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