Surface charges and surface potential in silicon surface inversion layers

The effect of interface charges on the channel conductance in MOS transistors has been investigated. It has been found that, by measuring the conductance as a function of temperature, it is possible to determine both the "fixed" interface charge which is independent of the surface potential and the charge trapped in surface states whose occupancy is a function of the surface potential. The characteristics of the two charge components are discussed. It appears that neither a continuous nor a delta-function energy distribution alone is adequate to describe the observed surface-state density.