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.

Date of Award	Aug 1970
Original language	English
Awarding Institution	Aston University