Generation of LO‐Phonons in a Time‐Dependent Electric Field at the Surface of III – V Materials

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Abstract
Recent experiments with ultrashort light pulses have shown that in the semiconductor samples under study the surface field is screened so quickly that it can generate coherent LO‐phonons. A theoretical description of this effect necessitates the simultaneous consideration of a number of interacting quantities: the exciting light field, the time dependent distributions of electrons and holes evolving towards equilibrium, the LO‐phonon amplitude, and the electric field self‐consistent with monopolar and dipolar charges. It turns out that the wave‐like nature of electronic distributions plays a decisive role via quantum mechanical boundary conditions. In the theory presented here this is accounted for by the use of a real space density matrix description.