Lecturer: Prof. Michael Wilkinson from the Open University
Abstract:
I shall give theoretical explanations of
two experimental observations of universal
behaviour in semiconductor systems.
The fist concerns the dependence of
photoconductivity $G$ upon light intensity $I$.
It is typically found that $G=I^\gamma$. Simple kinetic
theory indicates that we should expect
$\gamma=1$ or $\gamma=1/2$, but experimentally
values close to $\gamma =3/4$ or $\gamma=2/3$
are often observed, with $I$ varying over several decades.
I shall present a new explanation for these universal
exponents.
The second universality concerns exciton spectroscopy
in heterostructures. The linewidth $W$ of the absorption line
and the Stokes shift $S$ of the luminescence peak relative
to the absorption peak are found to be related by $S/W=0.6$
in most systems for which both values are published.
This ratio is independent of the degree of disorder and
of the composition of the semiconductors forming the
heterostructure, with $W$ varying over two decades.
I shall also give a quantitative explanation of this result.
Finally I point out what these two phenomena have in
common.