Low-frequency noise measurements were performed on grain boundaries that were Czochralski and Stepanov grown, obtained by diffusion `sticking' of different slices of silicon, and polycrystalline resistors, diodes, and transistors with polycrystalline emitters. It was found that in different cases the typical features were that both the potential fluctuation model and mobility fluctuation model were observed. Different contributions to the current noise made grain boundaries that were situated parallel and perpendicular to the carrier's current. Some discrepancy between existing noise models, real noise electrical circuit, and current noise temperature dependence of polycrystalline resistors were shown. These facts lead us to regard conclusions of existing models with care. Investigations of diode and transistor current noise show that the peculiarity of polycrystalline silicon demonstrates itself not only in the properties of base regions but also in the p-n junction regions.
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