  In recent years, the hybridization of hyperbolic van der Waals
heterostructures with plasmonic two-dimensional nano-materials is one of the
interesting research areas at THz frequencies due to the coupled features of
the hybrid structure. This article investigates the propagation of tunable
surface phonon-plasmon polaritons in grounded hybrid graphene-hexagonal Boron
Nitride (hBN) heterostructures. An analytical model is presented for the
proposed structure, by applying the boundary conditions for the electromagnetic
components in the various regions, to derive an exact dispersion relation. The
structure is simulated and the results are reported in the upper Reststrahlen
band. A good agreement is seen between simulation and analytical results, which
shows the high accuracy of our mathematical relations. The tunability of the
heterostructures is shown by studying the effect of chemical potential on the
performance of the structure. A high value of the figure of merit, i.e.
FOM=190, is reported at the frequency of 48.3 THz. The presented study can open
the way for the design of novel THz devices for future nano-plasmonic
applications.
