Figure 107: Plot of the dielectric function over the photon energy. At every maximum the valence and
the conduction bands are parallel
13.1.2 Inter- and Intraband Transition
Transition can take place from a filled into an empty state. For an insulator only interband transition
is possible, because they only have full valence bands and empty conduction bands.
For metals and semiconductors either inter- or intraband transitions are allowed. Intraband transition
means that transition in the same band is possible. When there are regions, where the conduction
band and the valence band are parallel, peaks in the absorption will be observed. Parallel bands
means, that a photon can excite a lot of states in the conduction andin the valence band. This effect
is shown in fig. 107. At every maximum (particular energy, e.g. ΛorXin fig. 107) the bands are
parallel. This measurement is very important to understand the band structure.
The condition for absorption is:
~ω = Ec(k)−Ev(k)