Generation of coherent acoustic phonons in piezoelectric semiconductor heterostructures

We review some experimental and theoretical aspects of coherent acoustic phonon generation in piezoelectric semiconductor multiple quantum wells. In order to model more advanced and complicated nano-acoustic devices, a macroscopic continuum theory for the generation and propagation of coherent acoustic phonons in piezoelectric semiconductor heterostructures is presented. The macroscopic approach is applicable in the coherent regime, and can be easily utilized to study coherent acoustic devices based on piezoelectric semiconductor heterosutructures. For each phonon mode, the corresponding coherent acoustic field obeys a loaded string equation. The driven force has contributions from the piezoelectric and deformation potential couplings. We applied the theory to model the generation of coherent longitudinal acoustic phonons in (0001)-oriented InGaN/GaN multiple quantum wells. The numerical results are in good agreement with the experimental ones. By using the macroscopic theory, we also investigated the crystal-orientation effects on the generation of coherent acoustic phonons in wurtzite multiple quantum wells. It was found that coherent transverse acoustic phonons dominate the generation for certain orientation angles.