Quantum kinetic influences on electron-phonon scattering in semiconductors

The dynamics of photoexcited electrons in GaAs due to LO phonon emission is investigated. On an ultrafast timescale energy conservation is seen to be violated and non-Markovian memory effects are observed. Initially, the phonon replica are substantially broadened with respect to the unrelaxed excitation peak. As time proceeds, quantum interference becomes operative resulting in a narrowing of the maxima to the shape expected in the semiclassical limit. The timescale for these phenomena is given by the LO oscillation period. Quantum kinetic simulations based on a simplified model that allows an exact treatment of the memory effects agree with our experimental data.