Picosecond Time Resolved X-ray Diffraction Measurements of Coherent Phonons and Carrier Dynamics at a Buried Interface

We present time resolved X-ray diffraction (TRXD) experiments on the transport of a coherent acoustic wave-packet and nonlinear carrier relaxation processes across the nearly ideal AlGaAs/GaAs interface. A femtosecond laser impulsively excites the underlying substrate such that the coherent acoustic phonons take the form of two counter propagating unipolar strain pulses and associated hot carrier dynamics. Picosecond TRXD is used to observe the laser-induced strain separately for the film and substrate.