COHERENT PHONONS IN SEMICONDUCTORS AND SEMICONDUCTOR HETEROSTRUCTURES

The impulsive excitation and phase-sensitive detection of coherent pho nons enable the study of dynamical properties of the lattice. In pump- probe experiments with femtosecond time resolution the amplitude and p hase of the coherent lattice motion can be detected with high sensitiv ity. Especially in semiconductors and semiconductor heterostructures, where a coherent phonon mode and free carriers are exited at the same time, important information about the carrier-phonon system far away f rom equilibrium is obtained. In bulk GaAs coherent plasmon-phonon mode s can be traced via the associated macroscopic field. In GaAs-AlGaAs b ased heterostructures coupled phonon-intersubband plasmons, coupled Bl och-phonon oscillations, and coherent acoustic phonons are observed.