THEORY OF OPTICAL-ABSORPTION IN DIAMOND, SI, GE, AND GAAS

We report first-principles calculations of epsilon(2)(omega) for diamo nd, Si, Ge, and GaAs that include the electron-hole interaction in det ail. The only essential experimental input is the crystal structure of the materials. Comparison with reflectivity and ellipsometry measurem ents allows us to assess the validity of the approximations made in th e calculation. We conclude that the approximation of singly excited el ectronic states and a statically screened electron-hole interaction is sufficient to understand the main features of the absorption spectra of these materials in the visible to near ultraviolet. [S0163-1829(98) 51416-6].