The document discusses crystal structures of solids, including semiconductors. It describes the basic unit cell and lattice structures, such as simple cubic, body-centered cubic, and face-centered cubic. Common semiconductor materials like silicon and gallium arsenide are discussed. Their crystal structures, including diamond and zinc blende, are explained. The document also covers crystal planes, directions, defects, and growth methods of semiconductor materials.

1. Chapter1
TheCrystalStructure
ofSolids
Inthischapter,
(i)Youshouldbeabletosketchtheatomicarrangementofatomsinthecubic
lattices.
(ii)Youshouldbeabletocalculatetheareaandvolumedensityofatoms.
(iii)Youshouldbeabletoidentifytheprincipalcrystaldirectionsandlattice
planesinthecubiclattices.
Dr.AbdulManafHashim1

2. CrystalStructureofSolidsDr.AbdulManafHashim2
SemiconductorMaterials
SemiconductorConductor/MetalInsulator
ConductivityHighLow
ElementalCompound
GroupIVofperiodictable
・Silicon(Si)
・Germanium(Ge)
・Carbon(C)
CombinationsofGroupIIIand
GroupVElements
・Binary:GaAs,AlAs,AlP,GaN,GaP,InPetc.
・Ternary:AlGaAs,InGaAs,InGaPetc.
CombinationsofGroupIVand
GroupIVElements
・SiC,SiGeetc.
IIIIVV
BC
AlSiP
GaGeAs
InSb
Periodictable
SiliconisthemostcommonmaterialforICs.

3. CrystalStructureofSolidsDr.AbdulManafHashim3
TypesofSolids
AmorphousPoly-crystallineSingle-crystalline
Haveahighdegreeoforder
,orregulargeometricperiodicity,
throughouttheentirevolumeof
material.
Haveahighdegreeoforder
overmanyatomicormolecular
dimensions.
Haveorderonlywithina
fewatomicormolecular
dimensions.
Itselectricalpropertiesare
superiortothoseofanon-single
crystalmaterial.
Grain
Grainboundariestendto
degradetheelectrical
characteristics.

4. CrystalStructureofSolidsDr.AbdulManafHashim4
SpaceLattices
a1
b1
b2
a2
b1
a1
b4
a4
b3
a3
A
C
D
B
・Theconcerninthislecturewillbethesinglecrystal.Arepresentativeunit,orgroupofatoms,is
repeatedatregularintervalsineachofthethreedimensionstoformthesinglecrystal.
・Theperiodicarrangementofatomsinthecrystaliscalledthelattice.
PrimitiveandUnitCell
・Latticepoint:arepresentationofaparticularatomicarraybyadot.
・Thesimplestmeansofrepeatinganatomicarrayisbytranslation.
・Two-dimensionallatticecanbetranslatedadistancea1inonedirectionandadistanceb1ina
secondnoncolineardirection.
・Athirdnoncolineartranslationwillproducethethree-dimensionallattice.
・Thetranslationdirectionsneednotbeperpendicular.
Infinitetwo-dimensionallattice
Variouspossibletwo-dimensionallattice/unitcell

5. CrystalStructureofSolidsDr.AbdulManafHashim5
・Wecanseethatsingle-crystallatticeisaperiodicrepetitionofagroupofatoms.Therefore,wedo
notneedtoconsidertheentirelattice.Wejustneedtoconsiderafundamentalunit.
・Aunitcellisasmallvolumeofthecrystalthatcanbeusedtoreproducetheentirecrystal.
Aprimitiveunitcell
・Aprimitivecellisthesmallestunitcellthatcanberepeated
toformthelattice.
・Inmanycases,itismoreconvenienttouseaunitcellthatis
notaprimitivecell.
・Unitcellsmaybechosenthathaveorthogonalsides,whereas
thesidesofaprimitivecellmaybenonorthogonal.
・Thisfigureshowsageneralizedthree-dimensionalunitcell.
・Therelationshipbetweenthiscellandthelatticecanbecharacterizedbythreevectors,and.
whichneednotbeperpendicularandwhichmayormaynotbeequalinlength.
wherep,qandsareintegers.
a
v
c
v
b
v
csbqapr
vvvv
++=

6. BasicCrystalStructures
CrystalStructureofSolidsDr.AbdulManafHashim6
(a)Simplecubic:
anatomlocatedateach
corner.
(b)body-centeredcubic(bcc):
hasanadditionalatomatthe
centerofthecube.
(c)face-centeredcubic(fcc):
hasadditionalatomsoneach
faceplane
Byknowingthecrystalstructureofamaterialanditslatticedimensions,wecandetermine
severalcharacteristicsofthecrystal.Forexample,wecandeterminethevolumedensity
ofatoms.

7. CrystalStructureofSolidsDr.AbdulManafHashim6
Example1.1:Tofindthevolumedensityofatomsinacrystalthatisabody-centeredcubic
withalatticeconstanta=5Å=5x10-8cm.
Solution:
Acorneratomissharedbyeightunitcellswhichmeetateachcornersothateachcorneratom
effectivelycontributesone-eighthofitsvolumetoeachunitcell.Theeightcorneratomsthencontribute
anequivalentofoneatomtotheunitcell.Ifweaddthebody-centeredatomtothecorneratoms,each
unitcellcontainsanequivalentoftwoatoms.
Thevolumedensityofatomsisthenfoundas
Comment:
Thevolumedensityofatomsjustcalculatedrepresentstheorderofmagnitudeofdensityformost
materials.Theactualdensityisafunctionofthecrystaltypeandcrystalstructuresincethepacking
density–numberofatomsperunitcell-dependsoncrystalstructure.
()
322
38
1061
105
2
cm/atomsx.
x
atoms
Density==−

8. CrystalPlanesandMillerIndices
CrystalStructureofSolidsDr.AbdulManafHashim7
Surfaces,orplanesthroughthecrystal,canbedescribedbyconsideringtheinterceptsof
theplanealongthe,andaxesusedtodescribethelattice.a
v
c
v
b
v
Threebasicplanesthatarecommonlyconsideredinacubiccrystalareshownbelow.
Fig.(a):Theplaneisparalleltotheandaxessotheinterceptsaregivenasp=1,q=infinityands=infinity.
Takingthereciprocal,weobtaintheMillerindicesas(1,0,0),sotheplaneisreferredtoasthe(100)plane.
Note:AnyplaneparalleltotheoneshowninFig.(a)andseparatedbyanintegralnumberoflatticeconstants
isequivalentandisreferredtoasthe(100)plane.
OneadvantagetotakingthereciprocaloftheinterceptstoobtaintheMillerindicesisthattheuseofinfinity
isavoidedwhendescribingaplanethatisparalleltoanaxis.
(100)(110)(111)

9. CrystalStructureofSolidsDr.AbdulManafHashim8
CrystalDirection
Thedirectioncanbeexpressedasasetofthreeintegerswhicharethecomponentsofavectorinthat
direction.Forexample,thebodydiagonalinasimplecubiclatticeiscomposedofavectorcomponents
1,1,1.Thebodydiagonalisthendescribedasthe[111]direction.
Note:Thebracketsareusedtodesignatedirectionasdistinctfromtheparenthesesusedforthecrystal
planes.
Inthesimplecubiclattices,the[hkl]directionisperpendiculartothe(hkl)plane.
Thisperpendicularitymaynotbetrueinnoncubiclattices.
(100)
(110)(111)

10. CrystalStructureofSolidsDr.AbdulManafHashim5
DiamondStructure
SiliconandGermaniumaretwoexamplesofsemiconductormaterialsthathaveadiamondcrystal
structure.Aunitcellofthediamondstructureismorecomplicatedthanthesimplecubicstructures.
Aunitcellofdiamondstructure
Animportantcharacteristicofthediamondlatticeisthatanyatomwithinthediamondstructurewillhave
fournearestneighboringatoms.
Thediamondstructurereferstotheparticularlatticeinwhichallatomsareofthesamespeciessuchas
siliconorgermanium.

11. TheZincblendeStructure
CrystalStructureofSolidsDr.AbdulManafHashim5
Aunitcellofzincblendestructure.Ex:GaAslattice
Thezincblendestructurediffersfromthediamondstructureonlyinthattherearetwodifferenttypesofatoms
inthelattice.Compoundsemiconductors,suchgalliumarsenide(GaAs)havethezincblendestructure.
Note:Theatomsinboththediamondandzincblendestructuresarejoinedtogethertoformatetrahedron.

12. AtomicBonding
CrystalStructureofSolidsDr.AbdulManafHashim5
Thetypeofbond,orinteraction,betweenatomsdependsontheparticularatomoratomsinthecrystal.
Ifthereisnotastrongbondbetweenatoms,theywillnot“sticktogether”tocreateasolid.
(i)IonicBonding:Acoulombinteractionbetweenoppositelychargedions.
Ex:Sodiumchloride(NaCl)
MaterialsofGroupIandVII.
(ii)CovalentBonding:Sharingofelectronsbetweentwoatoms,sothatineffect
thevalenceenergyshellofeachatomsisfull.
MaterialsofGroupIV.
(iii)MetallicBonding
(iv)VanderWaalsBonding

13. CrystalStructureofSolidsDr.AbdulManafHashim1
ImperfectionsandImpuritiesinSolids
Inarealcrystal,thelatticeisnotperfect.Itcontainsimperfections(defects)
andimpurities.
Imperfections(defects);thatis,theperfectgeometricperiodicityisdisruptedin
somemanner.Imperfectionstendtoaltertheelectricalpropertiesofamaterial.
ImperfectionsinSolids
(i)LatticeVibrations:duetothermalenergywhichisafunctionoftemperature.
VacancyInterstitial
(ii)PointDefects
(a)Vacancy(b)Interstitial

14. LineDislocation
Substitutional
Impurity
Interstitial
Impurity
CrystalStructureofSolidsDr.AbdulManafHashim5
(iii)LineDefects
(a)Linedislocation
Effectsofdefects:
・Disruptionofthenormalgeometricperiodicityofthelattice
andtheidealatomicbondsinthecrystal.
・Thechangeofelectricalpropertiesofmaterials.
ImpuritiesinSolids

15. CrystalStructureofSolidsDr.AbdulManafHashim1
GROWTHofSEMICONDUCTORMATERIALS
Successinfabricatingverylargescaleintegrated(VLSI)circuits/
ultralargescaleintegrated(ULSI)circuitsisaresultofpuresingle-crystalsemiconductor
materials.
Presently,Silicon,hasconcentrationsofmostimpuritiesoflessthan1partin10billion.
Togethighpurityofsemiconductormaterials,weneed;
(i)Extremecareinthegrowthprocesses,
(ii)Highgrowthtechnologies,
(iii)Extremecareateachstepofthefabrication
processes.
(1)GrowthfromaMelt
Acommontechniqueforgrowingsingle-crystal
materialssuchassilicon,iscalled
“Czochralski”method.
Chuck
Seed
Crystal
Heater
Crucible
Melt
Tube
Container

16. CrystalStructureofSolidsDr.AbdulManafHashim1
(2)EpitaxialGrowth
Epitaxialgrowthisaprocesswherebyathin,single-crystallayerofmaterialisgrownonthe
surfaceofasingle-crystalsubstrate.
Substrate(GaAs)Substrate(Si)
Epitaxiallayer(Si)Epitaxiallayer(AlGaAs)
HomoepitaxialGrowthHeteroepitaxialGrowth
EpitaxialGrowthTechnique
(i)ChemicalVaporDeposition(CVD)
(ii)LiquidPhaseEpitaxy(LPE)
(iii)MolecularBeamEpitaxy(MBE)
(iv)MetalOrganicVaporPhaseEpitaxy(MOVPE)/MetalOrganicChemicalVapor
Epitaxy(MOCVD)

17. CrystalStructureofSolidsDr.AbdulManafHashim1
Summary
・Afewofthemostcommonsemiconductormaterialswerelisted.
Siliconisthemostcommonsemiconductormaterial.
・Thepropertiesofsemiconductorsandothermaterialsaredeterminedtoa
largeextentbythesingle-crystallatticestructure.Theunitcellisasmallvolume
ofthecrystalthatisusedtoreproducetheentirecrystal.Threebasicunitcells
arethesimplecubic,body-centeredcubic(bcc)andface-centeredcubic(fcc).
・Siliconhasthediamondcrystalstructure.Atomsareformedinatetrahedral
configurationwithfournearestneighboratoms.Thebinarysemiconductorshave
azincblendelattice,thatisbasicallythesameasthediamondlattice.
・Millerindicesareusedtodescribeplanesinacrystallattice.Theseplanesmay
beusedtodescribethesurfaceofasemiconductormaterial.TheMillerindices
arealsousedtodescribedirectionsinacrystal.
・Imperfectionsdoexistinsemiconductormaterials.Afewoftheseimperfections
arevacancies,substitutionalimpurities,andinterstitialimpurities.Smallamounts
ofcontrolledsubstitutionalimpuritiescanfavorablyaltersemiconductorproperties.

18. CrystalStructureofSolidsDr.AbdulManafHashim1
Summary(cont.)
・Abriefdescriptionofsemiconductorgrowthmethodswasgiven.Bulkgrowth
producesthestartingsemiconductormaterialorsubstrate.Epitaxialgrowth
canbeusedtocontrolthesurfacepropertiesofasemiconductor.
・Mostsemiconductordevicesarefabricatedintheepitaxiallayer.
GlossaryofImportantTerms
Binarysemiconductor
Ternarysemiconductor
CovalentBondingDiamondLattice
Doping
Elementalsemiconductor
Compoundsemiconductor
Epitaxiallayer
IonImplantation
Lattice
MillerIndices
PrimitiveCell
UnitCell
Substrate
ZincblendeLattice
WurtziteLattice
IonBonding