Analytic approach to the a.c. conductance method for rapid characterization of interface states in MOS structures

Abstract

Nicollian and Goetzberger's well known integral expression for the equivalent parallel conductance due to interface states G p / ω has been given a simple analytical representation which is valid under the condition that interface potential fluctuation parameter σ > 1.5. Previous methods of conductance analysis based upon numerical and/or graphical construction are provided with alternative analytic relations. The earlier parametric numerical relations like ξ p, f w, f D and ln( ξ +/ ξ −) vs σ are described very well by analytic expressions in this paper. A new relation is presented to determine interface state time constant from the width of conductance peak. A new method is presented to determine dependence of σ on interface band bending from G p / ω vs bias measurements at just two frequencies. The expedient method of Nicollian, Goetzberger and Lopez utilises the same two curves to determine distribution of interface state density N ss and capture cross section σ p across the band gap. Therefore using the present new method for σ determination and other analytical relations for N ss and σ p determination, the expediency of their method is greatly enhanced. Complete conductance analysis for rapid characterization of the interface is shown to become now a simple straight forward affair, and the amount of data required is also substantially reduced.