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Upon completion of viewing thispresentation, you should be able to: Name at least three semiconductor materials

and state the most widely used.

Define doping and name the two types ofsemiconductor material formed with doping.

Explain how current flows in semiconductormaterial.

Explain the behavior of electrons and holes insemiconductor

Describe the carrier transportation in terms ofdrift and diffusion.

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The goal of electronic materials isto generate and control the flow ofan electrical current.

Electronic materials include:1. Conductors: have low resistance

which allows electrical current flow

2. Insulators: have a high resistance so

current does not flow in them3. Semiconductors: can be act as good

conductors or as good insulator

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Semiconductors are materials thatessentially can be conditioned to act asgood conductors, or good insulators, orany thing in between.

Common elements such as carbon,silicon, and germaniumare

semiconductors. Silicon is the best and most widely used

semiconductor.

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The maincharacteristic of asemiconductorelement is that it

has four electronsin its valence orbit.

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The unique capability

of semiconductoratoms is their ability tolink together to form aphysical structurecalled a crystallattice.

The atoms linktogether with oneanother sharing their

outer electrons. These links are called

covalent bonds.

2D Crystal Lattice Structure

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If the material is pure semiconductor materiallike silicon, the crystal lattice structure forms anexcellent insulator since all the atoms are

bound to one another and are not free forcurrent flow.

Good insulating semiconductor material is

referred to as intrinsic.

Semiconductor material is often used as aninsulator.

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To make the semiconductor conductelectricity, other atoms called impuritiesmust be added.

Impurities are different elements.

This process is called doping.

Doping : an intrinsic semiconductor isadded with a certain amount ofimpurities.

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Intrinsic semiconductoradded with an impurityhas 5 valance electronssuch as:arsenic,phosphorousand antimony

Adding arsenic willallow four of the arsenicvalence electrons tobond with the siliconatoms.

The one electron leftover for each arsenicatom becomesavailable to conductcurrent flow

This will develop an N-type material

Si

e

e

e

As e

e

e

e

ee

Si

e

e

e

e

e

e

e

Si

e

ee e

Si

e

Impurity: Arsenic Atom Extra Electron Outer Orbit

Donor impurity

contributes free

electrons

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Intrinsic semiconductor

added with an impurityhas 3 valance electronssuch as :aluminium,boron, gallium

The material will create

holes (+VE charge) This will develop an P-

type material

Holes become a type

of current carrier likethe electron to supportcurrent flow

Si e

e

e

B e

e

e

e

Si

e

e

e

e

e

e

e

Si

e

ee e

Si

e

Impurity: Boron Atom Hole Outer Orbit

Acceptor impurity

creates hole

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The goal of electronic materials is togenerate and control the flow of anelectrical current.

Two current mechanisms which causecharge to move in semiconductors thatis :

Drift Diffusion

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The movement of free carrier insemiconductoe due to an electric field

from externally applied voltage.

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In N-type material themajority carrier is electronwhile minority carrier is hole.

The DC voltage source has apositive terminal thatattracts the free electrons inthe semiconductor and pullsthem away from their atoms.Then the atoms will be leftwith positive charge.

Electrons from the negativeterminal of the supply enterthe semiconductor materialand are attracted by thepositive charge of the atomsmissing one of theirelectrons.

Current flows from the

positive terminal to thenegative terminal.

e e

ee

e

e

e

e

e

e

e

e

+-E

Direction of Electron Flow

Current

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In P-type material themajority carrier is hole whileminority carrier is electron.

Electrons from the negativesupply terminal areattracted to the positiveholes and fill them.

The positive terminal of the

supply pulls the electronsfrom 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.

+ +

++

+

+

+

+

+

+

+

+

+-E

Direction of Hole Flow

Current

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In its pure state, semiconductor material is anexcellent insulator.

The commonly used semiconductor material issilicon.

Semiconductor materials can be doped with other

atoms to add or subtract electrons. An N-type semiconductor material has extra

electrons. A P-type semiconductor material has a shortage of

electrons with vacancies called holes.

The heavier the doping, the greater theconductivity or the lower the resistance. By controlling the doping of silicon the

semiconductor material can be made asconductive as desired.