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The authors demonstrated that the piezoelectric superlattice, can serve as narrow-band detectors for propagating coherent longitudinal acoustic phonons at multiple frequencies corresponding to the spatial frequency of the superlattice and its higher harmonics, and its detection bandwidth is determined by the total structure width. By optically exciting a broadband propagating longitudinal acoustic pulse from a thin Ni film, the authors studied the acoustic spectral sensitivity function of a ten-period In0.12Ga0.88N/GaN multiple quantum well. Because the barriers (19 nm) and wells (3.6 nm) are of different widths, the second detection band, corresponding to the second harmonic of the fundamental frequency, can be resolved. [ABSTRACT FROM AUTHOR]

The authors demonstrate the generation of coherent acoustic phonons in (111)-strained InGaAs/GaAs multiple quantum wells through piezoelectric coupling by an optical pump-probe technique. Dependence of the induced strain amplitude on the photocarrier density reveals that coherent acoustic phonons can be efficiently excited by the piezoelectric effect with an unscreened built-in electric field. Under high fluence excitation, the generation of coherent acoustic phonons saturates. The experimental results are supported by a macroscopic theoretical model. No backward Raman signal and no zone-folded phonon modes were observed in this low impedance-mismatch and finite-period heterostructure. [ABSTRACT FROM AUTHOR]