  Epitaxial graphene (EG) produced from SiC surfaces by silicon sublimation is
emerging as a material for electronic applications due to its good electronic
properties and availability over large areas on a semiconducting substrate. In
this contribution, we report on the transport of charge carriers in EG on SiC
using high-frequency ($>$ 1 GHz) surface acoustic waves (SAWs). In our devices,
the EG is coated with hydrogen-silsesquioxane, SiO$_2$ and a ZnO layer. This
allows the efficient generation of SAWs and is compatible with the deposition
of a metal top gate. Measurements of frequency- and time-resolved power
scattering parameters confirm the generation and propagation of SAWs with
frequencies of up to more than 7 GHz. Furthermore, the ZnO coating enhances the
acoustoelectric currents by two orders of magnitude as compared to our previous
uncoated samples. These results are an important step towards the dynamic
acoustic control of charge carriers in graphene at gigahertz frequencies.
