Excitonic effect in the optical spectrum of semiconductors

The electron-hole interaction plays an important role in the optical spectra of semiconductors, not only in bound excitons in the energy-gap region, but also in the continuum. In particular, it affects the strength of the two major peaks in the absorption spectra of semiconductors of diamond and zinc-blende structures. A simple model is made to account for the band-structure effects. The Bethe-Salpeter equation containing the electron-hole interaction effect is solved to yield the absorption spectra for Si and Ge. A physical explanation of how the excitonic effects correct the strength of the $E_1$ and $E_2$ peaks in the right direction shows that our conclusions can be generalized to the III-V and II-VI compounds.