The estimation of doping profiles in gallium arsenide using capacitance measurements

Abstract

Measurement of the capacitance (C) of Schottky diodes as a function of voltage (V) is widely used to probe doping profiles in GaAs but the theory that is used is oversimplified and does not work well when the doping changes rapidly with distance. The region beyond the maximum of an implanted Gaussian profile for GaAs is of particular interest in connection with ingot qualification tests and it is just there that the problem is the most serious. We investigated some technically important aspects of the C(V) method by numerical simulation. The doping profile is input into a program, which then predicts the profile that will be obtained if the C(V) method is applied to a specimen with this assumed doping profile. It is found that the estimated maximum doping is not excessively in error and that although the predicted profile is indeed too high in the tail region, differences in constant background doping or in simulated tails due to channelling give differences in the predicted profile that are fairly close to the actual differences in doping. This is important for some practical applications. The estimation of the "percentage activation" of the implanted dopant is analyzed. Fitting a truncated Gaussian to the C(V)-derived profile is shown to give a useful estimate of the input dose.