Coherent phonon dynamics in short-period InAs/GaSb superlattices

► We performed ultrafast spectroscopy studies on InAs/GaSb-based short-period superlattices. ► We observed two types of coherent phonons with fast (1–2ps) and slow (∼24ps) periods. ► The fast phonons can be explained as acoustic phonons generated within the superlattice. ► This fast mode provides a determining of the superlattice period and assessing interface quality. ► The slow mode can be understood as a propagating coherent phonon wavepacket. We have performed ultrafast pump-probe spectroscopy studies on a series of InAs/GaSb-based short-period superlattice (SL) samples with periods ranging from 46Å to 71Å. We observe two types of oscillations in the differential reflectivity with fast (∼1–2ps) and slow (∼24ps) periods. The period of the fast oscillations changes with the SL period and can be explained as coherent acoustic phonons generated from carriers photoexcited within the SL. This mode provides an alternative method for determining the SL period. The period of the slow mode depends on the wavelength of the probe pulse and can be understood as a propagating coherent phonon wavepacket modulating the reflectivity of the probe pulse as it travels from the surface into the sample.