Theory for the laser-induced instability of the diamond structure of Si, Ge and C

Abstract

We examine the effect of a dense electron-hole plasma on the stability of the diamond lattice of elemental semiconductors. Such a plasma may result from an intense laser pulse. Using a tight-binding model for the electronic structure, we obtain that all transverse acoustical phonons of Si, Ge or C become instable if more than 8% of the electrons are excited from the valence band into the conduction band. This instability first destroys the cubic symmetry of the diamond lattice and then leads to a very rapid melting. These results agree well with recent experiments on Si surfaces.