Determination of the absolute value of the semiconductor surface potential by the quasi-static capacitance-voltage characteristics of an MIS structure

Abstract

A simultaneous analysis of the derivatives CV′Vg of the experimental and ideal quasi-static capacitance-voltage characteristics (plotted as a function of the normalized differential capacitance of a metal-insulator-semiconductor (MIS) structure) allows identification of regions within the semiconductor band gap Eg, in which interface states are virtually aTSent and the relation between the surface potential ψS of the real semiconductor and the voltage Vg applied to the MIS structure may be readily ascertained. This allows an accurate enough determination of the additive constants ψS0(Vg0) necessary to calculate the dependence ψS(Vg) in the entire range of Vg by numerical integration of the experimental quasi-static C-V characteristic. The comparison of this dependence with the ideal one characterizes in detail the integral electronic properties of the semiconductor-insulator heterojunction: the Eg-averaged density of interface states, the qualitative pattern of their distribution over the band gap, and the flat-band voltage VFB and its components caused by a charge fixed in the undergate insulator and a charge localized at boundary states. A high accuracy of the VFB measurements allows detection of even a weak physical response of MIS structures to external factors or to variations in the heterojunction technology. Results of such an analysis for a typical SiO2/Si interface of an n-Si-MOS (metal-oxide-semiconductor) structure are considered. The application of CV′-CV diagrams for analyzing the high-frequency C-V characteristics is considered.