Amplification of space charge waves of millimeter wave range in transversely inhomogeneous n-GaN Films

Amplification of space charge waves (SCW) due to the negative differential conductivity in n-GaN films placed onto a semi-infinite substrate is investigated theoretically. A general case of transverse inhomogeneous films is considered. The diffusion-drift equations for volume electron concentration were used jointly with the Poisson equation for the electric field. The transverse inhomogeneity results in a decrease of the electron mobility near the surfaces of the film due to surface scattering and, correspondingly, to some decrease of spatial increments of amplification. It is demonstrated that the non-uniform doping can compensate an influence of the surfaces on the spatial increments. It is possible to observe an amplification of SCW in n-GaN films of submicron thicknesses at high frequencies f ges 100 GHz. Also, due to amplification, high (~10 kV/cm) output electric fields of the short wave part of the millimeter wave range can be obtained.