Principles of Semiconductor Devices-L30
Transcript of Principles of Semiconductor Devices-L30
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Lecture 30: Heterojunction Bipolar Transistor (I)
Mu amma As ra u A am Mar Lun [email protected]
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Outline
1. Introduction
2. Equilibrium solution
for
heterojunction
3. T es of hetero unctions
4. Conclusions
“Heterostructure Fundamentals,” by Mark Lundstrom, Purdue
University, 1995.
Herbert Kroemer, “Heterostructure bipolar transistors and integrated
circuits,” Proc. IEEE , 70, pp. 13‐25, 1982.
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How to make a better Transistor
2n
,
, 2,i
E t
poly ballis ics E
t B N n υ
→ × ×
Heterojunction bipolar
transistor
Polysilicon Emitter
( ),
,
,, ,
2
,
g B
gg E BC B V B
E
E i B E N N ee
nβ
β
−
−
−= ≈
,
, , ,
g
C E V i E E n e
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Heterojunction Bipolar Transistors
i) Wide gap Emitter HBT
n
emitter
n
collector n+
p+base
EG1>EG2EG2 EG2
ii) Double Heterojunction Bipolar Transistor
n
emitter
n
collector n+
p+base
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EG1>EG2 EG2 EG3>EG2
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Mesa HBTs
nemitter
ncollector n+
p+
base
EG1>EG2 EG2 EG3>EG2
p+ base
nMesa HBT
n‐co ector
n+
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sem ‐ nsu a ng su s ra e
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Applications
1 O tical fiber communications
‐40Gb/s…….160Gb/s
2) Wideband, high‐resolution DA/AD converters
and digital frequency synthesizers
‐military
radar
and
communications
3) Monolithic, millimeter‐wave IC’s (MMIC’s)
‐front ends for receivers and transmitters
future need for transistors with 1 THz power ‐gain cutoff freq.
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Background
A heterojunction bipolar transistor
Kroemer
Schokley realized that HBT is possible, but Kroemer really
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.
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Outline
1. Introduction
.
3. Types
of
heterojunctions4. Conclusions
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Topic Map
signal
SignalDiode
Schottky
BJT/HBT
MOS
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Bandgaps and Lattice Matching
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Band Diagram at Equilibrium
( ) D A D q p n N N + −
∇ • = − + −
1n∂
Equilibrium
N N N r g
t q= • − +
∂
J = + ∇n E D n DC dn dt=0
1P P P
pr g
∂= ∇ • − +J
Small signal dn/dt ~ jωtn
Transient ‐‐‐ Charge control model
P P Pqp E qD pμ = − ∇J
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N‐Al0.3Ga0.7As: p‐GaAs (Type‐I Heterojunction)
D A
χ2
EC
EF
χ1
E G
≈ 1.42 eV
V
E
G≈ 1.80 eV
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rupt unct on
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Built‐in Potential: Boundary Condition @Infinity
21 2 21 gi ,bqV E + + = − ΔΔ + χ χ
qVbi
E
χ2
χ
Δ1
Δ2
Eg,2
EV
EF
2 2 1 2 1bi g ,qV E Δ Δ= − − + − χ
N N
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2
2 1
12g , B B E / k T
V , C ,
n N N e
−= −
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Interface Boundary Conditions
‐
Position
xn xp
( ) ( )0 0210 0 E E κ ε κ ε − +=
0 2 0
0
1
0dx dxκ ε κ ε
− +
=
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Analytical Solution for Heterojunctions
Charge D nq x N −
xpxn x , 0
0A
s E
p N q x E
k ε
+ =
E‐field, 0s B
D n A p x x
k
N N
ε
⇒ =x
( ) ( )0 0n p E x E xV
− +
= +
x
22
2 2
pn D Aq xq N
k k
x N
ε ε = +
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, ,
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Base Emitter Depletion Region
D A
xn xp
N x N x= ,0 ,2 s B Bs E N x V ε κ κ =
22
,, B p BE E n BE qN xqN x
=
, ,
,,
n
E B s E E Bsq N N N κ κ +
,0 ,2 s E Bs E N ε κ κ
,0 0,2 2s E s Bε κ ε κ ( ),, p bi
B B s E E Bsq N N N κ κ +
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Outline
1. Introduction
.
3. Types of heterojunctions
4. Conclusions
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P‐Al0.3Ga0.7As : n‐GaAs (Type I junctions)
E
0
Vacuum level
χ 1 qV ( x) qV BI
E
C V
jP
E l
E C
G≈ . e
V jn
C
E F
E V E G
≈ 1.42 eV
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V V
Depletion layerDepletion
layer
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(AlInAs/InP) Type II Junctions
D A
χ2
EC
EF
χ1
V
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N‐Al0.3Ga0.7As : n‐GaAs Junctions
‘Isotype Heterojunction’
E C E
E V
E ≈ 1.80 eV
E G
≈ 1.42 eV
E
E
V
V
Accumulation LayerDepletion
Layer
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Metal-Metal junctions have similar features …
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P‐GaSb : n‐InAs (Type III)
E 0
Field‐free vacuum level
χ
1
E
C χ 2
E
V
E FP
G≈ . e
E C E
Fn E
G≈ 0.36 eV
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E V
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P‐GaSb : n‐InAs (Type III)
E C Δ E
C = 0.87 eV
≈
E
V
C
E
E F
G
E G
≈ 0.36 eV
Accumulation Layer!Accumulation Layer!
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Conclusion
1. Heterojunction transistors offer a solution to the
‐ .
2. Equilibrium solutions for HBTs are very similar to those of
normal BJTs.
3. De endin on the ali nment there could be different
types of heterojuctions. Each has different usage.
. .
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