introduction semi materials

8/3/2019 Introduction Semi Materials

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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.

introduction semi materials

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