▎ 摘　　要

We consider high-frequency response of a system consisting of drifting electrons in a highly doped graphene and surface polar optical phonons of a polar substrate. We obtain the dielectric function, the frequencies and the decrement/increment of cooperative plasmon-optical phonon oscillations for this interacting system. We find that the response depends significantly on the degree of nonequilibrium for the electrons. In particular, the interaction between drifting plasmons and surface polar optical phonons leads to instability of the electron subsystem due to Vavilov-Cherenkov effect. We suggest that the hybrid system, a graphene on a polar substrate, is capable of using in amplifiers or generators of THz electromagnetic radiation.