| dc.description.abstract | This thesis considers the effect of a magnetic field on
the transition from a conducting to a non-conducting state in impurity
semiconductors, with particular reference to indium antimonide.
Two models for such a transition have been proposed: one
is based on the disappearance of bound states of the impurity due
to screening by conduction electrons and the other is based on the
onset of conduction due to overlap between the electron wave functions
on adjacent impurity sites. The present work extends the
latter model to include the effect of magnetic fields.
The theoretical work of Yafet, Keyes and Adams (Ref. 6),
Fenton and Haering (Ref. 5) and Durkan and March (Ref. 10) is reviewed
in Section 2 of the thesis. In Section 3 a dielectric approach
to impurity conduction, due to Frood (Ref. 12), is introduced;
he shows that the impurity system is non-conducting when
(see document for formula) where N is the impurity concentration, a is the
average polarizability of an impurity atom and CQ is the dielectric
constant of the background crystal. We use this criterion in
Section 4 to calculate a value of the critical magnetic field needed
to make conduction cease, deriving a as a function of magnetic
field from a variational calculation of the ground state energy of
the impurity. Our calculation is carried out for (see document for formula) so that
the impurities are all in the ground state and there are no electrons in the conduction band (i.e. we do not consider excited
states of the impurity or screening by conduction electrons).
Finally we compare theoretical predictions with published experimental
results. | |
