Coherent terahertz acoustic vibrations in polar and semipolar gallium nitride-based superlattices

The femtosecond optical pump-probe technique is used to generate and detect the coherent acoustic vibrations with a frequency 0.83x10(12) Hz in polar (0001) and semipolar (1122) InGaN/GaN superlattices. The measured amplitude of the vibrations in the semipolar sample is about five times smaller that in the polar one. Analysis of the experimental data and theoretical estimates suggest that, in addition to piezoelectric, deformation potential provides essential contribution to both generation and detection of vibrations, especially in the semipolar superlattice.