Many-Particle Effects in the Optical Excitations of a Semiconductor

We present (a) a general formulation of the electron-hole interaction which takes into account both screened electron-hole attraction and its exchange counterpart, giving rise to the excitonic and local-field effects, respectively; (b) a quantitative calculation of absorption and modulation spectrum in Si, which demonstrates the dominant role played by the continuum-exciton effect on the main optical absorption of a covalent semiconductor; and (c) a model analysis of the continuum-excitonic effect on the optical excitations of semiconductors in general.