Investigations of electron scattering mechanisms at the silicon-silicon dioxide interface
Edwards, John Richard
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https://hdl.handle.net/2142/25808
Description
Title
Investigations of electron scattering mechanisms at the silicon-silicon dioxide interface
Author(s)
Edwards, John Richard
Issue Date
1970
Doctoral Committee Chair(s)
Sah, C.T.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
electron scattering mechanisms
silicon-silicon dioxide interface
surface conductivity mobility
semiconductor space-charge region
Language
en
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."
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