A Study of the Galvomagnetic and Resistivity Properties of Thin Bismuth Films

Abstract

The results of the measurements of the resistivity, Hall coefficient and magnetoresistance of thin bismuth films are presented. The films were prepared by thermal evaporation of 99.999 % bismuth at <5 x 107° torr and shown to consist of oriented polycrystallites whose grain size was a function of the film thickness. The range of thicknesses investigated was from 200 = 4500 Å and observations are reported at temperatures between 29°K and 300°K in transverse magnetic fields to 12 kilogauss. The longitudinal resistive and transverse Hall voltages were measured by a null method. The resistivity of the films exceeded the bulk values and displayed a negative temperature coefficient. Surface scattering processes predominated at temperatures below approximately 160°K, the additional resistivity contribution being an oscillatory function of the film thickness. The thinnest films abet a saturation in the resistivity resulting from the shape of the Fermi surfaces. The Hall coefficient of bulk polycrystalline material was dominated by the negative coefficient, R⊥ but increased crystallite orientation in the films displaced the curve to a positive ordinate. A field variation of the carrier density was demonstrated and mathematically analysed. The Hall coefficient was shown to be an oscillatory function of the film thickness. The exponential-type increase in magnetoresistance at low temperatures occuring in bulk material was not observed in thin films, the limitations on the carrier path by the crystallite boundaries accounting for the greatly reduced magnetoresistancee. The carrier density and mobilities at various film thicknesses are presented as functions of temperature. The oscillatory nature in the thickness dependence of the resistivity, Hall coefficient, magnetoresistance and carrier mobility is attributed to a quantum size effect. A period of 400 Å was observed consistent with the theoretical predictions and gives a de Broglie wavelength of 800 Å for electrons and 200 Å for holes.