ELECTRONIC STRUCTURE

Optical spectroscopy in the form of reflectivity or ellipsometry measurements is among the
principal sources of information about the electronic structure of crystalline semiconductors.
Pronounced structures in the reflectivity or the imaginary part of the dielectric constant are
related to singularities in the so-called joint density of'states which can in most cases be
identified with direct, i.e. k-vector conserving, optical transitions between occupied valence and
empty conduction states at points of high symmetry in the Brillouin zone of the crystal. The
knowledge of the transition energies at these special points in k-space is in most cases sufficient
to construct a reliable and accurate band structure of the semiconductor with the help of
sophisticated band structure calculations.