Nonlinear interaction of space charge waves of millimeter wave range in nonuniform n-GaN films

The nonlinear interactions of space charge waves (SCW) in n-GaN films are investigated theoretically. SCW are amplified due to the negative differential conductivity. The transversely nonuniform films are considered. The hydrodynamic diffusion-drift equations for volume electron concentration were used jointly with the Poisson equation for the electric field. The transverse inhomogeneity results in the decrease of the electron mobility near the surfaces of the film and in the decrease of spatial increments of amplification of SCW. The generation of the second and the third harmonics and the amplified signals at the combination frequencies is demonstrated.