introduction semi materials
TRANSCRIPT
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Introduction toIntroduction to
Semiconductor MaterialsSemiconductor Materials
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PrerequisitesPrerequisites
To understand this presentation, you shouldhave the following prior knowledge: Draw the structure of an atom, including electrons,
protons, and neutrons.
Define resistance and conductance. Label an electronic schematic, indicating current flow.
Define Ohms and Kirchhoffs laws.
Describe the characteristics of DC and AC (sine wave)
voltages.
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Student Learning OutcomesStudent Learning Outcomes
Upon completion of viewing this presentation, youshould be able to:
Define conductor, insulator and semiconductor, and
state the resistance or conductance of each.
Name at least three semiconductor materials and statethe most widely used.
Name the basic structure of material and explain how it
is formed with atoms.
Define doping and name the two types of
semiconductor material formed with doping.
Name the current carriers in N and P-type material.
Explain how current flows in semiconductor material.
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Electronic MaterialsElectronic Materials
The goal of electronic materials is togenerate and control the flow of anelectrical current.
Electronic materials include:
1. Conductors: have low resistance whichallows electrical current flow
2. Insulators: have high resistance which
suppresses electrical current flow3. Semiconductors: can allow or suppress
electrical current flow
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ConductorsConductors
Good conductors have low resistance soelectrons flow through them with ease.
Best element conductors include:
Copper, silver, gold, aluminum, & nickel Alloys are also good conductors:
Brass & steel
Good conductors can also be liquid: Salt water
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Conductor Atomic StructureConductor Atomic Structure
The atomic structure ofgood conductors usuallyincludes only oneelectron in their outershell.
It is called a valenceelectron.
It is easily striped from theatom, producing currentflow.
Copper Atom
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InsulatorsInsulators
Insulators have a high resistance so currentdoes not flow in them.
Good insulators include:
Glass, ceramic, plastics, & wood Most insulators are compounds of several
elements.
The atoms are tightly bound to one another
so electrons are difficult to strip away for
current flow.
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SemiconductorsSemiconductors
Semiconductors are materials that essentiallycan be conditioned to act as good conductors,or good insulators, or any thing in between.
Common elements such as carbon, silicon,
and germanium are semiconductors. Silicon is the best and most widely used
semiconductor.
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Semiconductor Valence OrbitSemiconductor Valence Orbit
The maincharacteristic of a
semiconductor
element is that it has
four electrons in its
outer or valence
orbit.
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Crystal Lattice StructureCrystal Lattice Structure
The unique capabilityof semiconductoratoms is their ability tolink together to form aphysical structure
called a crystal lattice. The atoms link
together with oneanother sharing their
outer electrons. These links are called
covalent bonds.2D Crystal Lattice Structure
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3D Crystal Lattice Structure3D Crystal Lattice Structure
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Semiconductors can be InsulatorsSemiconductors can be Insulators
If the material is pure semiconductor material likesilicon, the crystal lattice structure forms an excellentinsulator since all the atoms are bound to one anotherand are not free for current flow.
Good insulating semiconductor material is referred to
as intrinsic. Since the outer valence electrons of each atom are
tightly bound together with one another, the electronsare difficult to dislodge for current flow.
Silicon in this form is a great insulator. Semiconductor material is often used as an insulator.
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DopingDoping
To make the semiconductor conduct electricity,other atoms called impurities must be added.
Impurities are different elements.
This process is called doping.
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Semiconductors can be ConductorsSemiconductors can be Conductors
An impurity, or elementlike arsenic, has 5valence electrons.
Adding arsenic (doping)will allow four of the
arsenic valenceelectrons to bond withthe neighboring siliconatoms.
The one electron leftover for each arsenicatom becomes availableto conduct current flow.
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Resistance Effects ofDopingResistance Effects ofDoping
If you use lots of arsenic atoms for doping,there will be lots of extra electrons so theresistance of the material will be low andcurrent will flow freely.
If you use only a few boron atoms, there willbe fewer free electrons so the resistance willbe high and less current will flow.
By controlling the doping amount, virtuallyany resistance can be achieved.
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Another Way to DopeAnother Way to Dope
You can also dope a
semiconductor material with anatom such as boron that hasonly 3 valence electrons.
The 3 electrons in the outer orbitdo form covalent bonds with itsneighboring semiconductoratoms as before. But one
electron is missing from thebond.
This place where a fourthelectron should be is referred toas a hole.
The hole assumes a positive
charge so it can attract electronsfrom some other source.
Holes become a type of currentcarrier like the electron tosupport current flow.
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Types ofSemiconductor MaterialsTypes ofSemiconductor Materials
The silicon doped with extra electrons iscalled an N type semiconductor.
N is for negative, which is the charge of an
electron.
Silicon doped with material missing
electrons that produce locations called holes
is called P type semiconductor.
P is for positive, which is the charge of a hole.
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Current Flow in NCurrent Flow in N--type Semiconductorstype Semiconductors
The DC voltage source
has a positive terminal thatattracts the free electronsin the semiconductor andpulls them away from theiratoms leaving the atomscharged positively.
Electrons from thenegative terminal of thesupply enter thesemiconductor materialand are attracted by thepositive charge of theatoms missing one of theirelectrons.
Current (electrons) flowsfrom the positive terminalto the negative terminal.
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Current Flow in PCurrent Flow in P--type Semiconductorstype Semiconductors
Electrons from the
negative supply terminalare attracted to thepositive holes and fill them.
The positive terminal of thesupply pulls the electrons
from the holes leaving theholes to attract moreelectrons.
Current (electrons) flowsfrom the negative terminalto the positive terminal.
Inside the semiconductorcurrent flow is actually bythe movement of the holesfrom positive to negative.
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In SummaryIn Summary
In its pure state, semiconductor material is an excellent
insulator. The commonly used semiconductor material is silicon.
Semiconductor materials can be doped with other atoms toadd or subtract electrons.
An N-type semiconductor material has extra electrons.
A P-type semiconductor material has a shortage ofelectrons with vacancies called holes.
The heavier the doping, the greater the conductivity or thelower the resistance.
By controlling the doping of silicon the semiconductor
material can be made as conductive as desired.