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

A simultaneous analysis of the derivatives C V ′ V g 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 E g , in which interface states are virtually aTSent and the relation between the surface potential ψ S of the real semiconductor and the voltage V g applied to the MIS structure may be readily ascertained. This allows an accurate enough determination of the additive constants ψ S 0 ( V g 0 ) necessary to calculate the dependence ψ S ( V g ) in the entire range of V g 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 E g -averaged density of interface states, the qualitative pattern of their distribution over the band gap, and the flat-band voltage V FB and its components caused by a charge fixed in the undergate insulator and a charge localized at boundary states. A high accuracy of the V FB 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 SiO 2 /Si interface of an n -Si-MOS (metal-oxide-semiconductor) structure are considered. The application of C V ′- C V diagrams for analyzing the high-frequency C-V characteristics is considered.