Effects of spatially inhomogeneous oxide charge distribution on the MOS capacitance-voltage characteristics

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Abstract
The commonly assumed linear model of surface potential fluctuation using a Gaussian distribution is shown to be invalid. A macrocapacitor model previously proposed by us is used to analyze the effects of spatially inhomogeneous oxide charge distribution on the MOS C‐V characteristics at various rms oxide charge deviations and temperatures. It is shown that a Gaussian oxide charge distribution of rms value of as low as 1011 electrons/cm2 gives rise to a doubly peaked probability distribution of the surface potential fluctuation. Substantial errors in fast surface state density occur using either the low‐frequency capacitance (Berglund), the high‐frequency capacitance (Terman), or the temperature dependence (Gray‐Brown) analysis of the fast surface states from C‐V curves. A major source of error is in the value of the average surface potential which is changed substantially from the ideal case by the presence of inhomogeneous oxide charge distributions.