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Title:Investigations of electron scattering mechanisms at the silicon-silicon dioxide interface
Author(s):Edwards, John Richard
Doctoral Committee Chair(s):Sah, C.T.
Department / Program:Physics
Subject(s):electron scattering mechanisms
silicon-silicon dioxide interface
surface conductivity mobility
semiconductor space-charge region
Abstract:A detailed theoretical and experimental investigation was conducted to determine the possible scattering mechanisms of electrons at the silicon-silicon dioxide interface. Theoretical surface conductivity mobility in a semiconductor space-charge region for the temperature range 1000K to 4000K was calculated using a classical Boltzmann-Fuchs equation with constant field and constant relaxation time approximations. The surface scattering mechanisms were included in the Fuchs boundary condition for normally incident scattering. The mechanisms investigated are diffuse scattering, constant partially specular scattering, de Broglie wave scattering, and shielded Coulomb surface state scattering. The momentum relaxation time characteristic of the channel region was calculated by including the screening of the impurity ions by the electrons in the inversion region. Experimental surface conductivity mobility measurements using n-channel metal-oxide-semiconductor (MOS) transistors for a wide change in impurity concentration are compared with the theoretical curves. These transistors were fabricated with the lowest possible number of surface states. For thermally oxidized silicon surfaces with minimum surface states, diffuse scattering and constant "p" scattering do not explain the experimental results. The conclusion is that the surface scattering is not completely diffuse. At least two additional mechanisms must be considered for surface scattering mechanisms? de Broglie wave scattering and shielded Coulomb surface state scatteringo De Broglie wave scattering is particularly important for temperatures above 2000K and is the best one parameter model for surface scattering over the 1000K to 4000K temperature range. The surface roughness based on the above model is 3 to 6 ~ or a few lattice spacings, indicating that thermally oxidized silicon has a microscopically smooth surface. Surface state scattering still appears to exist even for minimum surface state conditions and is particularly effective for temperatures below 200 oK. The anisotropy in the surface conductivity, predicted classically by Ham and Mattis and quantum mechanically by Stern and Howard for the (110) surface of silicon, has been observed.. The quantum mechanical treatment has been extended to finite temperatures for comparison with experiment. The conclusion is that the effective mass approximation near the surface is plausible from both the anisotropy measurements and from the small values of the surface roughness. It is also concluded that a quantum mechanical treatment is necessary for low temperatures.
Issue Date:1970
Genre:Dissertation / Thesis
Rights Information:1970 John Richard Edwards
Date Available in IDEALS:2011-07-14
Identifier in Online Catalog:6065186

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