Narrow-band detection of propagating coherent acoustic phonons in piezoelectric InGaN/GaN multiple-quantum wells

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 In_0.12Ga_0.88N/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.