Molten zone recrystallized, as well as sheet-grown polycrystalline material, exhibited a minimum in the temperature dependence of the Hall mobility. A new model was proposed in order to explain this, which was based upon negatively charged grain boundaries in p-type material. This resulted in a potential well at the grain boundaries instead of the more usual potential barrier. A key feature of the model was that the space charge density at the grain boundary depended upon the Fermi level position, and therefore upon the temperature.

H.Nussbaumer, F.P.Baumgartner, G.Willeke, E.Bucher: Journal of Applied Physics, 1998, 83[1], 292-6