A simple method for determining the impurity distribution near a p-n junction

It is well known that the form of the dependence upon bias voltage of the incremental space-charge layer capacitance of an asymmetrically-doped junction depends (in a rather complicated way) upon the concentration profile of the impurity charge on the high-resistivity side. It is shown in this paper that this impurity profile is related, in a very simple way, to the dependence of the incremental space-charge layer elastance upon the total depletion charge in either half of the dipole layer. The incremental-elastance vs. charge relationship has been employed in a simple pulsed-charge automatic measurement system which yields the impurity profile directly, as the slope of an recording. The system has advantages for rapid evaluation of impurity distributions in the base regions of transistors. These same advantages apply for the high-resistivity sides of asymmetrically doped diodes, under circumstances in which the quick automatic plotting feature is needed, very high accuracy is not required, and the reverse saturation current of the junction is small.