Graded channel FET's: Improved linearity and noise figure

The characteristics of GaAs field-effect transistors were examined as a function of the channel doping profile in the direction perpendicular to the surface. Theoretical considerations predict that improved device linearity is expected for channel doping profiles with relatively low carrier concentrations near the surface. These predictions are experimentally confirmed by comparison of GaAs FET's fabricated with uniform (flat) and exponentionally varying (graded) carrier concentrations as a function of depth. In addition, the graded devices are observed to exhibit noise figures approximately 1 dB lower than those of uniformly doped devices of the same geometry.