Subpicosecond coherent carrier-phonon dynamics in semiconductor heterostructures

Coherent longitudinal-optical phonons are generated in semiconductor heterostructures. The coupling of the coherent, longitudinal-optic (LO) phonons to collective carrier excitations oscillating parallel to the growth direction of GaAs/Al0.36Ga0.64As quantum wells is investigated with femtosecond time-resolution. This coupling is found to be weak for small well widths and evolves towards the bulk plasmon phonon coupling at increased well widths. We present a theory for the dielectric function in the growth direction of the heterostructure and calculate the frequency response of the system on the pulsed optical excitation. It is shown that the observations are based on the coupling of coherent phonons to intersubband plasmons.