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8/9/2019 BAB 1 EE201
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EE 201
TOPIC 1:INTRODUCTION
TOSEMICONDUCTOR
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DEFINITION OF SEMICONDUCTOR
A semiconductoris a solidwhoseelectrical conductivityis in between that of a
conductorand that of an insulator, and can be
controlled over a wide range, either permanently or
dynamically.
Example of semiconductor !ilicon " #ermanium
2 EE201-semiconductor device
http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Conductorhttp://en.wikipedia.org/wiki/Electrical_insulationhttp://images.google.com.my/imgres?imgurl=http://www.woodlands-junior.kent.sch.uk/Homework/victorians/images/inventions/bulb.jpg&imgrefurl=http://www.woodlands-junior.kent.sch.uk/Homework/victorians/inventions.htm&h=101&w=76&sz=2&hl=en&start=14&tbnid=j8E4p-0-iZfSzM:&tbnh=83&tbnw=62&prev=/images%3Fq%3Djoseph%2Bswan%2Bthe%2Binventor%2Bof%2Bbulb%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa%3DGhttp://en.wikipedia.org/wiki/Electrical_insulationhttp://en.wikipedia.org/wiki/Conductorhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Solid8/9/2019 BAB 1 EE201
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Diagrams o !toms
Atom: negative electrons orbit a small
positive nucleus" EE201-semiconductor device
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Cont##
$ %iny particles of matter calledprotonsand neutronsma&e up
the center of the atom' electronsorbit li&e planets around a star.
$ %he nucleus carries a positive electrical charge, owing to the
presence of protons (the neutrons have no electrical charge
whatsoever), while the atom*s balancing negative charge resides
in the orbiting electrons.
$ %he negative electrons are attracted to the positive protons +ust
as planets are gravitationally attracted by the !un, yet the orbits
are stable because of the electrons* motion.
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Cont##
Electron shells in an atom were formerly designated by letter
rather than by number. %he first shell (n1) was labeled , the
second shell (n2) , the third shell (n/) , the fourth shell(n) , the fifth shell (n3) 4, the sixth shell (n5) 6, and the
seventh shell (n7) 8.
%he maximum number of electrons that any shell may hold is
described by the e9uation 2n2, where :n; is the principle
9uantum number. %hus, the first shell (n1) can hold 2 electrons' the second shell
(n2) < electrons, and the third shell (n/) 1< electrons. (=igure
below)
% EE201-semiconductor device
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& or'it ( s)e**
+ EE201-semiconductor device
http://images.google.com.my/imgres?imgurl=http://www.woodlands-junior.kent.sch.uk/Homework/victorians/images/inventions/bulb.jpg&imgrefurl=http://www.woodlands-junior.kent.sch.uk/Homework/victorians/inventions.htm&h=101&w=76&sz=2&hl=en&start=14&tbnid=j8E4p-0-iZfSzM:&tbnh=83&tbnw=62&prev=/images%3Fq%3Djoseph%2Bswan%2Bthe%2Binventor%2Bof%2Bbulb%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa%3DG8/9/2019 BAB 1 EE201
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8uestion 1
Allumminium has 1/electrons, determine the number of
electron at electron orbit>
8uestion 2
?arbon - 5 electron
#ermanium - /2 electron6hosphorus - 13 electron
E,!MP-E .UESTION
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C/!R!CTERISTICS OF E
NUMER
a*ence:%he electrons in the outer most shell, or valence shell, are &nown as valence
electrons. %hese valence electrons are responsible for the chemical properties of the
chemical elements.
1-/ ev - conductor
- can conduct an electrical current
- low resistance
3-< ev - insulator
- cannot conduct an electrical current
- high resistance ev - semiconductor
- ot easy to accept@throw away valence electron
from another atomic
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How Sharing of Electrons
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Distur'ing actor sta'i*it4 :5
eat
%emperature riseBoping (absorption)
6otential different.
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!d6antages o Si*icon
!i C can accept more overheat before
change to conductor. ess easily damaged by heat when soldering
Dery low lea&age current when reverse
voltage. (#e-high lea&age current)
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P5t47e and N5t47e c)aracteristics
?urrent carrier C free electron and hole
=ree electron C negative current carrierole C positive current carrier
Hole
Free electron
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2 T8PE OF SEMICONDUCTOR:
ntrinsic !emiconductor
- 6ure semiconductors.- Ex #ermanium " !ili&on
Extrinsic !emiconductor- 6ure semiconductor F impurity
- %his process called doping (absorption) process.- 2 categories of impurity C trivalen and pentavalen.
- Ex trivalen-Alluminium, Goron, #allium.
pentavalen-Antimoni, Arseni&, 6hosphorus
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Formation o N5t47e 6ure semiconductor (silicon) F pentavalen atom (arseni&)
%his creates an excess of negative (n-type) electron charge
carriers.
%he electrons are the majority carriers, while holes are the
minority carriersin -type materials
Si
Ar
!iSi Si
Si
Si Si Si
Si
Figure 1.6
Silicon absorb with Arsenik
=ree electron
1% EE201-semiconductor device
http://en.wikipedia.org/wiki/Majority_carrierhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Majority_carrier8/9/2019 BAB 1 EE201
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Formation o P5t47e
6ure semiconductor (silicon) F trivalen atom (ndium)
%he purpose of P5t47e do7ingis to create an abundance of
holes a hole behaves as a 9uantity of positive charge
the holes are the majority carriers, while electrons are the
minority carriersin 6-type materials
Si
In
!iSi Si
Si
Si Si Si
Si
Figure 1.7
Silicon absorb with Indium
the vacancy left behind by theelectron is &nown as a hole.
1+ EE201-semiconductor device
http://en.wikipedia.org/wiki/Majority_carrierhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Majority_carrier8/9/2019 BAB 1 EE201
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PN 9unctions
%hese are p-type and n-type semiconductors brought together
in close contact, creating what is called the depletion region.
%he *depletion region'is so named because it is formed from
a conducting region by removal of all free charge carriers,
leaving none to carry a current.
%he importance of this contact or +unction is the creating of a
region between the p and n layers where p-type holes can
recombine with n-type free electrons producing light, such as in
light emitting diodes(EBs).
1& EE201-semiconductor device
http://en.wikipedia.org/wiki/Depletion_regionhttp://en.wikipedia.org/wiki/Light_emitting_diodeshttp://en.wikipedia.org/wiki/Light_emitting_diodeshttp://en.wikipedia.org/wiki/Depletion_region8/9/2019 BAB 1 EE201
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PN 9unctions
1 EE201-semiconductor device
http://en.wikipedia.org/wiki/File:Pn-junction-equilibrium.pnghttp://en.wikipedia.org/wiki/File:PN_Junction_Open_Circuited.svg8/9/2019 BAB 1 EE201
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PN 9unctions
n 6 +unction ;it)out an e
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For;ard 'ias
=orward-bias occurs when the P-typebloc& is connected to the
positiveterminal of a battery and the N-typebloc& is connected
to the negativeterminal, as shown below
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For;ard 'ias
%he *holes* in the 6-type region and the electrons in the -type
region are pushed towards the +unction.
%his reduces t)e ;idt) o t)e de7*etion =one# %he positive charge applied to the 6-type bloc& repels the
holes, while the negative charge applied to the -type bloc&
repels the electrons.
As electrons and holes are pushed towards the +unction, the
distance between them decreases. %his *o;ers t)e 'arrier in7otentia*#
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For;ard 'ias
Hith increasing bias voltage, eventually the no conducting
depletion Ione becomes so thin that the charge carriers can
tunnel across the barrier, and t)e e*ectrica* resistance a**s toa *o; 6a*ue#
%he electrons which pass the +unction barrier enter the 6-type
region (moving leftwards from one hole to the next, with
reference to the above diagram).
An electron starts flowing around from the negative terminal tothe positive terminal of the battery.
%he thin depletion Ione produces very little electrical resistance
against the flow of electrons
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Re6erse 'ias
?onnecting the P-typeregion to the negativeterminal of the
battery and the N-typeregion to thepositiveterminal, produces
the reverse-bias effect. Gecause the 6-type region is now connected to the negative
terminal of the power supply, the *holes* in the 6-type region are
pulled away from the +unction, causing t)e ;idt) o t)e no
conducting de7*etion =one to increase#
2" EE201-semiconductor device
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Re6erse 'ias
!imilarly, because the -type region is connected to the
positive terminal, the electrons will also be pulled away from
the +unction. %his effectively increases t)e 7otentia* 'arrier and greatly
increases t)e e*ectrica* resistance against the flow of charge
carriers.
=or this reason there will be minima* e*ectric current across
t)e 9unction#
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For;ard and Re6erse 'ias
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RE!>DO?NS -IMIT
At the middle of the +unction of the p-n material, t)e de7*etion
region ;idens ;it) increasing re6erse 'ias#
%he e*ectric ie*d gro;s as t)e re6erse 6o*tage increases# Hhen the electric field increases beyond a critical *e6e* the
9unction 'rea@s do;n and currant begins to flow, usually by
either the Jener or avalanche brea&down processes.
Goth of these brea&down processes are non-destructive and
reversible so long as current density does not exceed levelsthat could cause thermal damage.
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I cur6e
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.UIC> REIE?
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Conc*usion:
EE201-semiconductor device23
Befine a semiconductor.
Explain the characteristics of -type and 6-type semiconductors.
llustrate the formation of a 6 +unction llustrate the meaning of forward biased voltage and reverse biased
voltage.
dentify the effects when a 6- +unction is supplied with forward biased
and reverse biased voltage on the following items
C
Area of depletion regionC Kunction resistance
C ?urrent flow (including lea&age current)
Explain why brea&down occurs when 6- +unction is reverse biased.