Influence of an impurity profile on the determination of interface states

Abstract

In order to determine the density of interface states from C(V) curves for high test frequencies, a comparison is made with a computed curve for uniform impurity concentration but identical minimum capacitance. The curves calculated for a doping profile (due, say, to acceptor depletion near the surface of a p-type semiconductor) are assumed to represent the measured C( V) curves of MOS diodes. A number of “charges in interface states” (8 × 10 10 cm −2 in the given example) are simulated by the impurity profile. This shows that it is not sufficient to introduce a mean effective substrate impurity concentration by adapting the minimum capacitance in the inversion region. The same accordingly applies for the C( V) curves for low test frequencies. The error due to “simulated interface states” is reduced somewhat, but it remains the altered relation between the applied voltage and the surface potential.