Phonon coupling in GaAs/Al_xGa_1-xAs observed by picosecond Raman scattering

The authors measure the hot phonon population of the GaAs LO phonons using a picosecond Raman scattering technique. Their samples were a series of GaAs/Al_0.4Ga_0.6As superlattices (SLS) with a fixed well width (L_z) and varying barrier width (L_b). An abrupt increase in the phonon generation rate was observed as L_b decreased over a narrow range. This is interpreted as the onset of significant well-to-well coupling of the confined GaAs LO phonons. An estimate of the LO phonon penetration depth into the Al_0.4Ga_0.6As barriers is obtained from this transition.