Model of Schottky junction admittance taking into account incomplete impurity ionization and large-signal effects

Abstract

A general model for the Schottky junction reverse bias admittance is created. The model takes into account incomplete impurity ionization and does not rely on the small-signal approximation, so that impurity rate equations are not linearized. The model is valid at arbitrary temperatures for an arbitrary periodic bias amplitude and harmonic content as long as the free-carrier relaxation time is much shorter than the bias period. Impurity ionization is treated in the framework of the Shockley-Read-Hall statistics; free-carrier distribution is assumed to be an equilibrium one. The model allows calculation of the junction potential distribution and thus the junction transfer function and admittance. Junction admittance is calculated for different ac bias amplitudes and the results are compared with the data obtained from the small-signal model. It is shown that the model fits experimental junction admittance more accurately than the small-signal model when the ac component of the potential is large with respect to the thermal potential k B T/q.