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Intrinsicemi-conductor
Materials
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Introduction
Intrinsic semiconductors aresemiconductors which do not contain
impurities. They do contain electrons as
well as holes. The electron densityequals the hole density since the
thermal activation of an electron from
the valence band to the conduction bandyields a free electron in the conduction
band as well as a free hole in the
valence band.
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Introduction
Intrinsic by denition means natural orinherent, and intrinsic semiconductors
are the bulk properties of the
semiconductor material itself, not thoseof dopants or impurities. Silicon and
germanium are the two most commonly
used eamples of intrinsicsemiconductors, as they are elementalsemiconductors and were some of the
rst widely studied and usedsemiconductors.
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Semiconductor Structure
The electronic structure ofsemiconductors are the foundation of
their unique properties. Themechanisms which make
semiconductors their own class ofmaterial is based on the electricalstructure, which dictates the core
properties of semiconductors.
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The most well known electricconductors are metals. !etals are able
to carry an electric "ow because of
their available free electrons that canpass from one atom to the net. This
enables the electric "ow #which is
merely composed of electrons "owingacross a substance$ to travel through
the length of the metal.
Semiconductor Structure
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Semiconductors work in a verydi%erent manner. &ll intrinsicsemiconductors are group 14
elements, and thusly only have 'valence ( electrons available forbonding in their outermost shell.
)ecause of these ' electrons, group*' elements like Silicon are able to
form crystal lattice structures
composed of countless atoms of that
Semiconductor Structure
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Semiconductor Structure
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Band Theory
!etals and semiconductors have aunique property that separates them
from non+conductive insulators. In
metals and insulators, the di%erencebetween energy orbitals are so small
that electrons can be ecited from lower
energy orbitals to higher energy levels.These small orbital energy di%erences
are referred to as bands.
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Band Theory
nlike the discrete energy levels thatyou are taught about in beginning
chemistry, these bands are so close
together in energy that it takes a verysmall amount of energy to promoteelectrons to these higher band levels.
The higher energy level that thevalence electrons can be ecited to isreferred to as the conduction band,
because the electrons in this band are
free to carry an electric current.
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Band Theory
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Hole Conduction
)y denition, an electron hole isthe opposite of an electron. It
represents the lack of an electronwhere an electron could potentially
be situated or previously wassituated in an otherwise full
electron shell. In this case,electron holes result from electrons
leaving their place in the lattice
structure .
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Hole Conduction
-nce heat is put into thesemiconductor and electrons begin
continually crossing into the
conduction band, hole conductionbegins constantly moving electronsacross the semiconductor, addingto the overall electron "ow. This
increases the conductive ability ofthe semiconductor, constantly
allowing new electrons to cross into
the conduction gap.
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Hole Conduction
lectron holes have an important rolein increasing the conductive abilitiesof semiconductors. /ole conduction
rst requires an electron toeperience ecitation in order to leave
its valence band to the conduction
band. -nce the valence electron hasleft, neighboring electrons are pulledinto the electron holes, lling eisting
electron holes while creating newneighboring ones.
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