Amplification and nonlinear interaction of space charge waves of microwave band in heterogeneous gallium nitride films

Abstract

Theoretical study of amplification and nonlinear interaction of space charge waves caused by negative differential conductivity in gallium nitride n-GaN films placed over a semi-infinite substrate is presented. A general case of transversally heterogeneous films is considered. Hydrodynamic diffusion-drift equations for bulk electron concentration together with Poisson equation are used. Transversal heterogeneity leads to decreased electronic mobility near the film’s surface and to decreased space amplification increments of space charge waves. Heterogeneous alloying may compensate the influence of surfaces on space amplification increments. Amplification of space charge waves in n-GaN films of sub-micron thickness on higher frequencies f ≥ 100 GHz is possible in comparison to n-GaAs films. High output electric fields ∼10 kV/cm can be obtained in the short-wave range of the millimeter band. Nonlinear interaction of space charge waves in n-GaN films is also considered using the diffusion-drift equation. The possibility of generating second and third multiples of input signal as well as amplification of combination frequencies is proven.