Interpretation of hall and resistivity measurements in polycrystalline silicon

Grain boundary barriers play a dominant role in the transport properties of polycrystalline silicon. As a result, resistivity and Hall measurements in polysilicon, when interpreted in the normal manner used for single crystals, do not represent in general the same physical entities as in single crystals. The bulk of the grain is more conducting and has a larger free carrier concentration than the barrier. However, the Hall voltage, from which the carrier concentration and mobility are computed, arises from both the bulk and the barrier region. For small grains (< 10μm) the contribution to the Hall voltage from the barrīer region is dominant, while for large grains (≥ 100μm) the bulk dominates. There is a transition region between the two. The magnitudes of the contributions depend on the relative size and resistivity of the grain and the boundary. Thus the interpretation of the data varies with grain size. Doping also affects the relative contribution of the bulk and barrier regions. It is not necessary to invoke carrier depletion within the grain to account for the observed mobility minimum.