The standard deviation sgr;sof the surface potential fluctuation on the Si‐SiO2interface was measured by means of the conductance technique of Nicollian and Goetzberger on a number of wafers with oxide charge densitiesQoxin the range (1–15) ×1010cm−2. We could not find a proportionality between sgr;2sandQoxas was derived in theoretical considerations by Brews but rather we have found a correlation between sgr;2sand the surface state densityNss. We show that the reason for this is that only charges in the immediate vicinity of the interface contribute to sgr;s. In a second experiment, mobile ions were drifted through the oxide by performing a temperature‐bias stress. The resulting change in sgr;2sis directly proportional to the accompanying change inQox, but the ratio of Dgr;sgr;2sto Dgr;Qoxis three times higher than would be expected from Brews’s model. A reason for this behavior might be that the interface charge is concentrated in some small patches rather than distributed homogeneously. The assumption of negative surface charge in our samples, however, is not necessary.
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