Optical absorption associated with grain boundaries in n-type germanium
McNatt, Jerrold Lloyd
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https://hdl.handle.net/2142/25722
Description
Title
Optical absorption associated with grain boundaries in n-type germanium
Author(s)
McNatt, Jerrold Lloyd
Issue Date
1967
Doctoral Committee Chair(s)
Handler, Paul
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
optical absorption
Grain Boundaries
n-type germanium
bicrystals
Language
en
Abstract
The optical absorption by 40 to 25 0 grain boundaries
in germanium bicrystals in the spectral region 0040 ev to
Oe80 ev was measured using two modulation techniques. The
first technique measured directly the difference in optical
absorption between the grain boundary layer and the adjacent
single crystal regions. The second technique measured the
changes in absorption produced when DC and AC electrical
biases were applied across the grain boundary.
Grain boundary absorption was found to be composed
of two relatively distinct components. One, which varies
in magnitude as the bias across the grain boundary is
variedp is due electric field-assisted absorption in the
grain boundary space charge layer. No other effects on
optical absorption due to applied bias were observed. The
second component was independent of applied bias. This
absorption occurs in the narrow (~ 100 A) deformed region
at the grain boundary plane and is probably due to the combined
effects of lattice disarray and broken covalent
bonds in this region.
This bias-independent component has an exponentiallike
dependence on photon energy in a spectral region of
from 0.60 to 0.75 ev (below the single crystal direct edge).
This implies an exponential-like joint density of states for
optical transitions which in turn implies exponential-like
densities of states for the band edges in the grain boundary
layero This exponential absorption structure is similar to
that observed for thin films of amorphous germanium and may
indicate that the higher angle grain boundaries have an
amorphous structure.
Observations on a pure 60 twist grain boundary
showed no significant difference when compared to measurements
of the pure tilt boundaries. This indicates that
the optical absorption probably arises from similar structural
features in the two types of grain boundary.
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