Depletion approximation analysis of the differential capacitance—Voltage characteristics of an MOS structure with nonuniformly doped semiconductors

The semiconductor equations relating the differential capacitance-voltage characteristics of an MOS structure with nonuniformly doped semiconductors have been derived by using the depletion approximation based on the rigorous definition of the depletion layer width. The relationship between the depletion layer width and the differential capacitance is shown to be the same as the one derived using classical model that is sometimes taken for granted. At the same time, it is shown that the differential capacitance arises from the introduction (or removal) of majority carriers from the abrupt space-charge edge. Expressions derived using this model that are necessary to obtain the impurity distributions are the same as those developed by Kennedy et al. The present model will permit the explicit analysis of subthreshold characteristics in ion-implanted MOSFET's even for non-space-charge neutral profiles.