Reflection amplification in thin layers of n-GaAs

Theoretical expressions are developed for the stability criterion and admittance of a thin coplanar GaAs reflection amplifier. The traveling-wave dispersion relation includes diffusion. The cathode boundary condition includes velocity modulation, injection, and distributed inhomogeneity effects. The admittance includes displacement currents running outside the semiconducting layer. The results show that the second to fifth harmonics may be more nearly unstable than the fundamental. Experiments on a coplanar epitaxial sample yield stable linear net gain at frequencies in the range 2 GHz-8 GHZ.