  The possibility to tune the functional properties of nanomaterials is key to
their technological applications. Superlattices, i.e., periodic repetitions of
two or more materials in different dimensions are being explored for their
potential as materials with tailor-made properties. Meanwhile, nanowires offer
a myriad of possibilities to engineer systems at the nanoscale, as well as to
combine materials which cannot be put together in conventional heterostructures
due to the lattice mismatch. In this work, we investigate GaAs/GaP
superlattices embedded in GaP nanowires and demonstrate the tunability of their
phononic and optoelectronic properties by inelastic light scattering
experiments corroborated by ab initio calculations. We observe clear
modifications in the dispersion relation for both acoustic and optical phonons
in the superlattices nanowires. We find that by controlling the superlattice
periodicity we can achieve tunability of the phonon frequencies. We also
performed wavelength-dependent Raman microscopy on GaAs/GaP superlattice
nanowires and our results indicate a reduction in the electronic bandgap in the
superlattice compared to the bulk counterpart. All our experimental results are
rationalized with the help of ab initio density functional perturbation theory
(DFPT) calculations. This work sheds fresh insights into how material
engineering at the nanoscale can tailor phonon dispersion and open pathways for
thermal engineering.
