band formation. semiconductors are insulators at 0 k and as the temperature rises their conductivity...
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Band formation
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Semiconductors are insulators at 0 K and as the temperature rises their conductivity increases. = ne2/m*
Semiconductors
Metal Insulator Semiconductor
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GaAs, AlAs, InAs, InP, GaP, AlP, InN, GaN, AlN, InSb, GaSb, AlSb and ternaries and quaternaries. AxB1-xCyD1-y
IV, III-V, II-VI Semiconductors
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Rede do diamante
Rede cristalina do diamante, do silício e do germânio
C, Si ou Ge
Rede cúbica de face centrada
Usados para eletrônica...
Duas redes transladadas de¼ da diagonal central
Cada átomo está ligado a 4 outros
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Tabela periódica dos elementos
IVIII V
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Rede Zincblend
Rede cristalina do GaAs, InP, AlGaAs, InAlAs...
Ga, In, Al
As, P
... e na opto-eletrônica
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Si Si
Si Si
Si
SiSiSi
Si
Si
Si
Si
Si
Si
Si
Elétrons ligados(BV)
Qual a energia necessária para liberar estes elétrons?
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Si Si
Si Si
Si
SiSiSi
Si
Si
Si
Si
Si
Si
Si
Elétrons livre(BC)
Falta de 1 elétron“buraco”
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E= hc/E= 1240 / (eV/nm)E= 1,24 / (eV/m)
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GaAs
AlAsInP InAs
InxGa1-xAsGaxAl1-xAs
GaP
InxGa1-xP InxAl1-xAs
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SemicondutoresEn
ergi
a do
elé
tron
BC
BV
Eg
Ener
gia
do e
létr
on
BC
BV
Eg
Eg pequeno
Posição Posição
Facilidade para elétrons saírem da BV para a BC
Temperatura e luzProbabilidade: exp(-Eg/kT)
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(.m) d/dT
Silício 3 x 103 -70 x 10-3
Cobre 2 x 10-8 4 x 10-3
Mecanismos de condução diferentes
+
- T
T
Aumento no número de portadores de carga
O aumento das vibrações cristalinas dificulta a passagem do elétron = m/ne2
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Nível de Fermi
f(E) = 1/(1 + exp((E-EF)/kT))
EnergiaEF
1
f(E)
T = 0K
T ≠ 0K
BV
BC
EF
Material intrínseco
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Dopagem p e n• Dopagem n se introduz um elemento com 1 elétron a mais
que o átomo a ser substituído.Exemplos: P no lugar de Si, Si no lugar de Ga, S no lugar de
As. As impurezas passam a se denominadas doadoras. Haverá um excesso de elétrons para condução.
• Dopagem p se introduz um elemento com 1 elétron a menos que o átomo a ser substituído.
Exemplos: B no lugar de Si, Si no lugar de As, Zn no lugar de Ga. As impurezas passam a se denominadas aceitadoras. Haverá um excesso de buracos para condução.
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Dopagem p e n
IVIII V Em relação ao Si:
mais um elétron (grupo V) – tipo n
Si – Ne + 3s2 3p2
As: Ar + 3s2 3p3
B: He + 3s2 3p1
menos um elétron (grupo III) – tipo p
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As Si
Si Si
Si
SiSiSi
Si
Si
Si
Si
Si
Si
Si
“Sobra” 1 elétron
Qual a energia necessária para liberar este elétron?
Impureza doadora
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Material tipo nEn
ergi
a do
elé
tron
BC
BV
Posição
Ed
Ener
gia
do e
létr
on
BC
BV
Posição
Ed
Do + Ed = D+ + e-
+
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B Si
Si Si
Si
SiSiSi
Si
Si
Si
Si
Si
Si
Si
“Falta” 1 elétron
Qual a energia necessária para liberar este elétron?
Impureza aceitadora
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Material tipo pEn
ergi
a do
elé
tron
BC
BV
Posição
Ea
Ener
gia
do e
létr
on
BC
BV
Posição
Ao + Ea = A- + h+
Ea
-