▎ 摘　　要

We theoretically study the generation of microwave radiation at frequency omega 1 - omega 2, produced by two microwaves, of frequencies omega 1 and omega 2, normally incident on monolayer graphene grown epitaxially on a SiC substrate and doped by electrostatic gating. Two mechanisms responsible for this third-order nonlinear effect are considered: (i) the graphene's conduction band nonparabolicity arising from the substrate-induced bandgap opening at the Dirac points of the graphene's Brillouin zone and (ii) the energy dependence of the electron-momentum relaxation time. Both mechanisms are incorporated in our Boltzmann-equation-based treatment of the graphene's third-order nonlinear response to the applied microwave radiation field. Within the framework of the approach, we evaluate the output power omega 1 - omega 2 of the omega 1 - omega 2 ) microwave radiation as a function of the graphene's carrier density n S controlled by the applied gate voltage. Our formulation predicts an unexpected nonmonotonous behavior of this function: there is a pronounced minimum in the omega 1 - omega 2 ( n S ), which is followed by a maximum. This finding may serve to provide a rational explanation for this type of oscillation as observed by Dragoman et al. [Appl. Phys. Lett. 97, 093101 (2010)] in the output power of the microwave harmonic generation in gated graphene, which are not properly construed so far.