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Course: ECE 4350, Spring 2007School: Villanova
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andDevices Topic17:MetalSemiconductorJunctions ECE3500SemiconductorMaterials andHeterojunctions Fall2007 Learning Objectives Inthistopicyouwilllearn: Howmetalsemiconductorjunctions resultineitherohmicorrectifying contacts Howpnjunctionsofdissimilarmaterials behavebothatthermalequilibriumand underbias. Metal-Semiconductor Junctions Theworkfunction,,ofamaterialis definedastheenergyrequiredto...
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andDevices
Topic17:MetalSemiconductorJunctions ECE3500SemiconductorMaterials andHeterojunctions
Fall2007
Learning Objectives
Inthistopicyouwilllearn: Howmetalsemiconductorjunctions resultineitherohmicorrectifying contacts Howpnjunctionsofdissimilarmaterials behavebothatthermalequilibriumand underbias.
Metal-Semiconductor Junctions
Theworkfunction,,ofamaterialis definedastheenergyrequiredto takeanelectronfromtheFermi leveltothevacuumlevel.
vacuum level q m EF
q S
q S
EC EF
metal
EV semiconductor
Metal-Semiconductor Junctions (contd)
Whenametalandasemiconductor arebroughtintointimatecontact,
Metal-Semiconductor Junctions (contd)
Consideranntypesemiconductor beingbroughtintocontactwithametal withworkfunctiongreaterthanthatof thesemiconductor.
eq m EF
q S
EC EF
metal
EV n-type semiconductor
Metal-Semiconductor Junctions (contd)
Metal-Semiconductor Junctions (contd)
Rectifying behavior i
V
Schottky Barrier
Metal-Semiconductor Junctions (contd)
Nowconsiderthecaseofanntype semiconductorbroughtintointimate m contactwithametalwith.< S
q m metal eq S
n-type Junctions semiconductor
Metal-Semiconductor (contd)
Metal-Semiconductor Junctions (contd)
Ohmic behavior i
V
OhmicContactallowscurrenttoflow easilyintoandoutofthe semiconductor.
Schottky Contact to p-type Semiconductor
Ohmic Contact to p-type Semiconductor
Heterojunctions
EC1
EC
EC2 EF2 EV2
E g = E g1 E g 2
EF1 Ev1
EV
qV01
= EC + EV
EC
EF
qV0 = q (V01 +V02 )
qV02
EV
V01 2 N d 2 = V02 1 N d 1
Procedure for Sketching Heterojunctions
Step1.AligntheFermilevelsofthetwo semiconductorsleavingspaceforthe transitionregion.
EC EF
EV
Procedure for Sketching Heterojunctions (contd)
Step2.Placethemetallurgicaljunctioncloser
tothemoreheavilydopedside.Atthispoint placeECandEV,separatedbythe appropriatebandgaps.
EC EF
EC EV
EV
Procedure for Sketching Heterojunctions (contd)
Step3.Connecttheconductionandvalence
bandskeepingthebandgapconstantineach region.
EC EF
EV
Summary
Inthistopicyouhavelearned: Howmetalsemiconductorjunctions resultineitherohmicorrectifying contacts Howpnjunctionsofdissimilarmaterials behavebothatthermalequilibriumand underbias.
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