Electrical Transport Properties of Thin Bismuth Films

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Abstract
The resistivity, Hall coefficient, and magnetoresistance coefficient of well ordered but twinned bismuth films were measured between 1. 15 and 300 K. It was found that the surface scattering in these films is not specular, contrary to the findings of some other workers. At 300 K the thickness dependence of the resistivity can be roughly fitted by the Fuchs-Sondheimer boundary-scattering theory with a surface reflection coefficient of 0.6, indicating partially diffuse scattering. It was also observed that the apparent scattering becomes more diffuse with decreasing temperature until at low temperatures the data can no longer be explained by the Fuchs-Sondheimer theory. This indicates that an additional size-dependent temperature-dependent scattering mechanism exists in thin-film transport. It was observed that at low temperatures the temperature dependence of the conductivity could be explained on the basis of a constant mean free path for the thicker samples. For thinner samples, the temperature dependence of the conductivity again indicates that there is an additional scattering mechanism that becomes stronger with decreasing temperature and decreasing sample thickness. Values of the mobility and mean free path, calculated from the data, were also observed to vary consistently with the sample thickness. The conclusions, drawn from the thickness dependence of the resistivity, concerning the diffuseness of the surface scattering of the charge carriers were confirmed by the dependence of the mean free path upon the sample thickness. Finally, quantum size-effect oscillations were observed in all of the transport properties of the thin bismuth films at low temperatures. The period (about 400 Å) and phase of the oscillations are in reasonable agreement with the theory and in good agreement with other values reported in the literature.

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