C-V profiling of GaAs FET films

The depletion layer capacitance of a Schottky barrier on a GaAs FET film can only be measured in series with the resistance of the undepleted portion of the film. This inherent series resistance may be significant at all values of bias and causes large errors in profile determinations. By treating the depletion layer capacitance and the series resistance as a distributed transmission line, it is possible to define an effective series resistance which can be related directly to the resistivity of the film. Using parameters typical of epitaxial films grown for GaAs FET applications, general criteria are developed for the profilability of these films. It is shown that, in general, films with small pinchoff voltages (i.e., films intended for low-noise FET applications)