MODULE 4.1

Semiconductors

Syllabus Part 66Module 4.1 (B1.1 Excluded) (B2 – Level

2)Materials, electron configuration,

electrical properties; P and N type materials: effects of

impurities on conduction, majority and minority characters;

PN junction in a semiconductor, development of a potential across a PN junction in unbiased, forward biased & reverse biased conditions;

Comments on SyllabusAlthough it is not included,

however, without knowledge of the semiconductor, a student will not be able to understand how a diode or transistor works.

Due to this requirement, the subject is included in the program.

IntroductionModern Electronics

◦19th Century – Thomas Edison discovered heated metal emitted charged particles. Led to discovery of thermionic valve.

◦1940 – transistor was invented by Bell Laboratories

◦1950s’ – development of integrated circuit◦ 1960s – prediction that the number of

transistors in IC would be doubled every 18 months.

◦2007 – an advanced IC contained 55 mil transistors

Atomic Structure◦1913 – Bohr – Beginning of the basic

theory of atomic structure.

Valence ShellThe tendency of atoms to gain

or loss electrons depends onthe number of electrons inthe outmost shell.

The outmost shell is known asvalence shell and the electrons is knownas valence electrons.

Energy Bands

x-axis- the allowed energy levels numbered from 1 to 5. The y-axis shows each level's energy in electron volts (eV)

One electron volt is the energy that an electron gains when it travels through a potential difference of one volt (1 eV = 1.6 x 10-19 Joules).

Energy in Atoms

As in previous slide, the energy level is discreet.

Electrons are in either conduction bands or valence band.

Materials with large amount of electrons in the conduction bands are good conductor.

Atoms of semiconductorsSilicon Germanium

Covalent BondingSingle Atom

Crystallize Structure/ lattice

Semi ConductorN Type

P Type

Conduction

Electron Flow Hole Flow

Intrinsic flow – there is no impurities added

Doped with Arsenic

Doping Process …A pure silicon or germanium are

insulator. It has valence electrons of 4.

Adding impurities will change the characteristic of the semiconductor.

If elements with 5 valent electrons is added, it will have one electron balance, thus become N-type, negative type with electrons as the current carrier.

… Doping ProcessIf an element with 3 electrons is added,

then it will be P-type with holes. P type or positive type will conduct current via holes, similar to the conventional flow of current.

Example of impurities for N-types are arsenic and phosphorous.

Example of impurities with 3 valent electron and used to manufacture P type semiconductor is boron, gallium and indium.

N-type semiconductorThe doping is done by 5 valence

electrons – pentavalent impurity.◦Example arsenic, antimony, bismuth

and phosphorous.

P-Type SemiconductorDoping with impurities with 3

valence electrons or trivalent will produce a P-type semi-conductor.◦Example of trivalent materials are –

alluminium, indium, gallium, boron◦Concept of minor and major carriers.

RESOURCES

Title Author

ISBN

Aircraft Electricity and Electronics

Eisman

0-02-801859-1

Art of Electronics Horowitz /Hill

Horowitz /Hill

0-521-37095-7

Elements of Electronics

Hickey/ Villines

0070286957

Modern Aviation Electronics

Helfrich

0-13-118803-8

Micro Electronics in Aircraft systems

E Pallet

0-273-08612-X

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