7/24/2019 3 - Semiconductors
1/34
SemiconductorsSemiconductors
11
7/24/2019 3 - Semiconductors
2/34
Three Types of MaterialsThree Types of Materials
CONDUCTOR
is any material that supports a generous flow of charge when a
voltage source of limited magnitude is applied across its terminal
less than 4 valence electrons in the outermost shell
22
7/24/2019 3 - Semiconductors
3/34
Three Types of MaterialsThree Types of Materials
NSU!"TOR#D$!$CTRC
is any material that offers a very low level of conductivity under
pressure from an applied voltage source
material that resists flow of charge
more than 4 valence electrons in the outermost shell
resistivity %&' is up to ()(*+,cm
e-amples are paper. dry wood. plastic. ru//er. mica. etc0
33
7/24/2019 3 - Semiconductors
4/34
Three Types of MaterialsThree Types of Materials
44
S$MCONDUCTOR
is a material that has aconductivity level somewhere
/etween the e-tremes of an
insulator and a conductor0
it acts as an insulator at
a/solute ) %) 1' and conducts atroom temperature
has 4 valence electrons in the
outermost shell
shows a reduction in
resistance with increase intemperature and is said to have
a negative temperature
coefficient
7/24/2019 3 - Semiconductors
5/34
Semiconductor MaterialsSemiconductor Materials
Common materials used in the development of semiconductor devices2
Silicon %Si'Silicon %Si' & 3 ) - ()& 3 ) - ()55+,cm+,cm is widely used in diodes. transistors and integrated circuitsis widely used in diodes. transistors and integrated circuits 6est 7uality silicon is o/tained /y growing crystals in a la/oratory6est 7uality silicon is o/tained /y growing crystals in a la/oratory
which is then fa/ricated intowhich is then fa/ricated into waferswafersoror chipschips
8ermanium %8e'8ermanium %8e'
& 3 ) +,cm& 3 ) +,cm 9ure germanium is a poor electrical conductor and /ecomes a9ure germanium is a poor electrical conductor and /ecomes a
semiconductor when impurities are addedsemiconductor when impurities are added :as used e-tensively in the early years /ut has /een shifted towards:as used e-tensively in the early years /ut has /een shifted towards
SiliconSilicon ;as a low voltage drop of )05
7/24/2019 3 - Semiconductors
6/34
Semiconductor MaterialsSemiconductor Materials
Common materials used in the development of semiconductor devices2
Selenium %Se'Selenium %Se' has a resistance that varies depending on the intensity of light that fallshas a resistance that varies depending on the intensity of light that falls
on it. a property =nown ason it. a property =nown asphotoconductivityphotoconductivity is used in photocellsis used in photocells the main advantage of selenium over silicon is that it can withstandthe main advantage of selenium over silicon is that it can withstand
/rief/rief transientstransientsoror surgessurgesof a/normally high voltageof a/normally high voltage
8allium "rsenide %8a"s'8allium "rsenide %8a"s' in comparison with Silicon. it needs less voltage and functions at higherin comparison with Silicon. it needs less voltage and functions at higher
fre7uencies /ecause the charge carriers move fasterfre7uencies /ecause the charge carriers move faster are relatively immune to the effects of ioni>ing radiation such as ?raysare relatively immune to the effects of ioni>ing radiation such as ?rays
and gamma raysand gamma rays is used in light@emitting diodes %!$D'. infrared@emitting diodes. laseris used in light@emitting diodes %!$D'. infrared@emitting diodes. laser
diodes. visi/le light and infrared detectors. ultra@high@fre7uencydiodes. visi/le light and infrared detectors. ultra@high@fre7uency
amplifying devices and a variety of integrated circuits %C'amplifying devices and a variety of integrated circuits %C' is more e-pensive to produce than siliconis more e-pensive to produce than silicon
66
7/24/2019 3 - Semiconductors
7/34
Semiconductor MaterialsSemiconductor Materials
Common materials used in the development of semiconductor devices2
Metal O-ideMetal O-ide Needs almost no power to function /ecause it draws so littleNeeds almost no power to function /ecause it draws so little
current that a /attery in a MOS %Metal O-ide Semiconductor'current that a /attery in a MOS %Metal O-ide Semiconductor'
device lasts longdevice lasts long
;as high speed which can /e used in operation at high;as high speed which can /e used in operation at highfre7uencies and ma=es it possi/le to perform calculations perfre7uencies and ma=es it possi/le to perform calculations per
secondsecond "re easily damaged /y static electricity"re easily damaged /y static electricity
77
7/24/2019 3 - Semiconductors
8/34
$nergy !evels$nergy !evels
The more distant the electrons from the nucleus. the higher the energy state and
any electron that has left its parent atom has a higher energy state than any
electron in the atomic structure0
88
7/24/2019 3 - Semiconductors
9/34
$nergy !evels$nergy !evels
oni>ation is the mechanism where/y an electron can a/sor/ sufficient energy
to /rea= away from the atomic structure and enter the conduction /and
99
$nergy 8ap %Ug or $g' or Aor/idden 6and is the energy difference /etween theconduction /and and valence /and0 t is the energy re7uired to move or transfer a
valence electron at the valence /and to the conduction /and
7/24/2019 3 - Semiconductors
10/34
$nergy !evels$nergy !evels
(0 ;ow much energy in Boules is re7uired to move a charge of C through adifference in potential of *
7/24/2019 3 - Semiconductors
11/34
Types of "tomic 6ondingTypes of "tomic 6onding
onic or $lectrovalent or $lectrostatic 6ondingonic or $lectrovalent or $lectrostatic 6onding Refers to the /onding resulting from the attractive forces of oppositelyRefers to the /onding resulting from the attractive forces of oppositely
charged ions %positive or negative'charged ions %positive or negative'
1111
Ionic compounds resu! "#en me!$s re$c! "i!# nonme!$s
%e!$s loseeec!rons !o m$!c# !#e number of valence electrons
o& !#eir ne$res! no'e ($s
Positive ions &ormwhen !#e num'er o& eec!rons $re ess !#$n
!#e num'er o& pro!ons
)roup 1 me!$s ion 1*
)roup 2 me!$s ion 2*
In ionic compounds+ nonme!$s in 15+ 16+ $nd 17 ($in eec!rons
&rom me!$s
,onme!$ $dd eec!rons !o $c#iee !#e oc!e! $rr$n(emen!
7/24/2019 3 - Semiconductors
12/34
Ionic Bond
Between atoms of metals and nonmetals
with very different electronegativity
Bond formed by transfer of electrons
Produce charged ions all states.
Conductors and have high melting point.
Examples !aCl" CaCl#" $#%
7/24/2019 3 - Semiconductors
13/34
7/24/2019 3 - Semiconductors
14/34
Ionic onds/ ne i( )reed #ie& o(
7/24/2019 3 - Semiconductors
15/34
1). Ionic bond& electron from !a is transferred to Cl" this
causes a charge imbalance in each atom. 'he !a becomes
(!a)*and the Cl becomes(Cl+*" charged particles or ions.
7/24/2019 3 - Semiconductors
16/34
Types of "tomic 6ondingTypes of "tomic 6onding
Metallic 6ondingMetallic 6onding
Refers to the type of /onding that is a product of theRefers to the type of /onding that is a product of theattractive forces of group of positive ions andattractive forces of group of positive ions and
electrons that are generally free to move a/outelectrons that are generally free to move a/out
among its ionsamong its ions
1616
,ormed between atoms of metallic elements
Electron cloud around atoms
-ood conductors at all states" lustrous" very high
melting points
Examples !a" ,e" l" u" Co
7/24/2019 3 - Semiconductors
17/34
%e!$ic onds/ %eo" do(s "i!#
pen! o& 'ones !o (o $round.
7/24/2019 3 - Semiconductors
18/34
%e!$ic ond+ e$ o& ec!rons
7/24/2019 3 - Semiconductors
19/34
/etals ,orm lloys
/etals do not combine with metals. 'hey form
lloys which is a solution of a metal in a metal.
Examples are steel" brass" bron0e and pewter.
7/24/2019 3 - Semiconductors
20/34
Types of "tomic 6ondingTypes of "tomic 6onding
Covalent 6ondingCovalent 6onding
s when atoms of materials share electrons with another atoms0s when atoms of materials share electrons with another atoms0The shared electrons are attracted simultaneously to the atomsThe shared electrons are attracted simultaneously to the atoms
resulting to a force that /inds them togetherresulting to a force that /inds them together
2020
Between nonmetallic elements of similar
electronegativity.
,ormed by sharing electron pairs
1table non+ioni0ing particles" they are not
conductors at any state
Examples %#
" C%#
" C#
23
" 2#
%" 1iC
7/24/2019 3 - Semiconductors
21/34
7/24/2019 3 - Semiconductors
22/34
"#en eec!rons$re s#$red equally
,,:
;V, ,
7/24/2019 3 - Semiconductors
23/34
2. Covalent bonds- 'wo atoms share one or more pairs of outer+shell
electrons.
Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom
Oxygen Molecule (OOxygen Molecule (O22))
;
http://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swf7/24/2019 3 - Semiconductors
24/34
"#en eec!rons$re s#$red 'u!
s#$red unequally
: ;V,
,
7/24/2019 3 - Semiconductors
25/34
o$r ;o$en! onds/ neen
m$!c#ed+ 'u! "iin( !o s#$re.
7/24/2019 3 - Semiconductors
26/34
+ water is apolarmoleculebecause oxygen is more electronegative than
hydrogen" and therefore electrons are pulled closer to oxygen.
7/24/2019 3 - Semiconductors
27/34
Covalent 6onding of SemiconductorsCovalent 6onding of Semiconductors
2727
Covalent Bonding of 1ilicon Crystal Covalent Bonding of -as Crystal
7/24/2019 3 - Semiconductors
28/34
Type of Semiconductor MaterialsType of Semiconductor Materials
NTRNSC M"T$R"!
" semiconductor that has /een carefully refined to reduce the impurities toa very low level H essentially as pure as can /e made availa/le through
modern technology
Relative Mo/ility is the a/ility of the free carriers to move throughout the
material
Note2 an increase in temperature of a semiconductor can result in a
su/stantially increase in the num/er of free electrons in the material
2828
emiconduc!or In!rinsic ;$rriers>per cu'ic cen!ime!er? :e$!ie %o'ii! @$c!or >An?>cm2BVCs?
-as 4.5 x 463 4766
1i 4.7 x 4646 8966
-e #.7 x 4648 766
$?TRNSC M"T$R"!" semiconductor material that has /een su/Iected to the doping process
7/24/2019 3 - Semiconductors
29/34
Boylestad and !ashels;y
Electronic Devices and Circuit TheoryCopyright
7/24/2019 3 - Semiconductors
30/34
n-typen-typeMaterialMaterial
is created /y introducing impurity elements that have five valence electrons
%pentavalent' such as antimony. arsenic. phosphorus and /ismuth
3030n!imon impuri! in n-!pe m$!eri$
,o!e/'he remaining
unassociated electron"
loosely bound to its
parent atom" isrelatively free to move
within the newly
formed n+type
material.
onor $!oms
diffused impurities
with five valence
electrons.
7/24/2019 3 - Semiconductors
31/34
p-typep-typeMaterialMaterial
is created /y introducing impurity elements that have three valence
electrons %trivalent' such as /oron. gallium. indium and aluminum
3131
,o!e/'he resultingvacancy will readily
accept a Afree
electron.
ccep!or $!oms
diffused impurities
with three valence
electrons.
oron impuri! in p-!pe m$!eri$
7/24/2019 3 - Semiconductors
32/34
$lectron vs ;ole Alow$lectron vs ;ole Alow
3232
7/24/2019 3 - Semiconductors
33/34
Two sets of currents flow in a diode2
Majority and Minority CarriersMajority and Minority Carriers
MaIority CarriersMaIority Carriers
The maIority carriers in n@type materials are electrons0 The maIority carriers inp@type materials are holes0
Minority CarriersMinority Carriers
The minority carriers in n@type materials are holes0 The minority carriers inp@type materials are
electrons0
3333
7/24/2019 3 - Semiconductors
34/34
n-type and p-typen-type and p-typeMaterialMaterial
3434
Top Related