semiconductorbasics.pptx

8/9/2019 SemiconductorBasics.pptx

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Semiconductor Basics

Chapter 1


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Atomic Structure

Elements are made of atoms 110 Elements; each has an atomic

structure Today, quarksand leptons, and their

antiparticles, are candidates for beingthe fundamentalbuilding blocks fromwhich all else is made!

Bohr odel toms ha"e planetary structure toms are made of nucleus#$rotons

#%& ' (eutrons& and electrons#)&

110 th element is called *armstadtium #*s&


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Atomic Structure

toms go around the nucleolus in their orbits+discrete distances

Each orbit has some energy le"el The closer the orbit to the nucleus the less

energy it has roup of orbits called shell Electrons on the same shell ha"e similar energy

le"el Valence shellis the outmost shell

-alence shell has valence electronsready tobe freed

(umber of electrons #(e& on each shell #n&

.irst shell has / electrons econd shell has electrons #not shown here&

(e 2 /n/


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Valence Shell

toms are made of "alence

shelland core

Core includes nucleus and

other inner shells .or a Carbon atom the atomic

number is 3

Core charge 2 3 $ % / e 2 #%3&%#)/&2#%4&

5emember the first shell has /

electrons


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Elements

Basic categories Conductors

E6amples7 Copper, sil"er 8ne "alence electron , the e

can easily be freed 9nsulators

-alence electrons are tightlybounded to the atom

emiconductors ilicon, germanium #single

element& allium arsenide, indium

phosphide #compounds& They can act as conductors or

insulators

Conduction bandis

where the electron

lea"es the "alence shell

and becomes free

-alence bandis where

the outmost shell is

lways free

electrons

.ree

electrons


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Semiconductors

5emember the further away from thenucleus the less energy is re:uiredto free the electrons

ermanium is less stable ess energy is re:uired to make the

electron to


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Conduction Electrons and Holes

Electrons e6ist only withinprescribed energy bands

These bands are separated by

energy gaps =hen an electron


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Conduction Electrons and Holes

Electrons e6ist only withinprescribed energy bands

These bands are separated by

energy gaps =hen an electron


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n impurity, or element likearsenic, has ? "alenceelectrons@

dding arsenic #doping& willallow four of the arsenic"alence electrons to bond with

the neighboring silicon atoms@ The one electron left o"er for

each arsenic atom becomesa"ailable to conduct current

flow@


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presentation ofeyst@org

Types of Semiconductor Materials

The silicon doped with e6tra electrons is

called an A( type semiconductor@ A( is for negati"e, which is the charge of an

electron@

ilicon doped with material missing electrons

that produce locations called holes is calledA$ type semiconductor@ A$ is for positi"e, which is the charge of a hole@


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Doping

By adding impurities to the intrinsicsemiconductor we can change theconducti"ity of the material + this is called

doping ()type doping $)type doping

()type7pentavalent #atom with ? "alenceelectrons& impurity atoms are added b#ntimony& % iD (egati"e charges #electrons& are generated()type has lots of free electrons

$)type7 tri"alent #atom with "alenceelectrons& impurity atoms are added B#Boron& % iD $ositi"e charges #holes& are generated $)type has lots of holes


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Diodes

( region has lots of free electrons $ region has lots of holes t e:uilibrium7 total number positi"e and negati"e

charges is the same #F room temp& t the pn


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Diodes


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Diodes


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ormation of depletion


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Biasing Types of a Diode

.orward bias Bias "oltage -BiasG barrier "oltage -Bar 5eduction in !and"ionssmaller

depletion region -Bar *epends on material, doping,

temp, etc@ #e@g@, for silicon it is 0@H -&

5e"erse bias Essentially a condition that pre"ents

electrons to pass through the diode

-ery small re"erse break down current arger depletion region is generated

Cathode

n regionnode

p region

Connected to the

negative side of

the battery

Connected to the

positive side of

the battery

I


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Biasing Types of a Diode #or$ard%

Cathode

n regionnode

p region

I

Moving

electrons

Small dynamic resistance

-Bias

np

Con"entional

Current .low

Conventional

Current lo$

& #or$ard%


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Very Small

Moving

Electrons'

(everse Current%

Biasing Types of a Diode #(everse%

Cathode

n regionnode

p region

I

)arge resistance

-Bias

np

Con"entional

Current .low

Holes are left

behind* large

depletion region

&nstant pull of

electrons


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