Characterization of Contact Resistivity on InAs/GaSb Interface
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Transcript of Characterization of Contact Resistivity on InAs/GaSb Interface
![Page 1: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/1.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Characterization of Contact Resistivity on InAs/GaSb Interface
Y. Dong, D. Scott, A.C. Gossard and M.J. Rodwell.
Department of Electrical and Computer Engineering,
University of California, Santa Barbara
[email protected] 1-805-893-3812 2003 Electronic Materials Conference
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University of CaliforniaSanta Barbara Yingda Dong
Motivations
Base resistance (RB) is a key factors limiting HBT’s high frequency performance.
8maxB BC
ff
R C
Sub-collector
Substrate
E
C
B
RB fmax
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University of CaliforniaSanta Barbara Yingda Dong
Base Resistance
Sub-collector
Substrate
E
C
B
A large contribution to base resistance:
Contact resistance between metal and p-type base
Metal
Ec
Ev
Ef
+
Tunneling
Contact resistivity on p-type material is usually much higher than on n-type material.
Reason: holes have larger effective mass than electrons.
![Page 4: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/4.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Base contact on n-type material
Is it possible to make the base contact on n-type material?
S.I. substrate
N+ subcollector
SiO2 N- collector
P+ base
SiO2
P+N+
Base metal
P+N+
Base metal
Emitter
Emitter contact metal
CollectorMetal
Collector Metal
Base metal contact on n-type extrinsic base RB could be reduced
Metal to base contact over field oxide CBC can be reduced
Large emitter contact area RE can be reduced
High ft , fmax , ECL logic speed…
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University of CaliforniaSanta Barbara Yingda Dong
S.I. substrate
Polycrystalline Base Contact in InP HBTs
1) Epitaxial growth 2) Collector pedestal etch, SiO2 planarization
N+ subcollector
N- collector
P+ base
S.I. substrate
N+ subcollector
SiO2 subcollector
P+ base
SiO2
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University of CaliforniaSanta Barbara Yingda Dong
Polycrystalline Base Contact in InP HBTs
3) Extrinsic-base regrowth 4) Deposit base metal, encapsulate with SiN, pattern base and form SiN sidewalls
S.I. substrate
N+ subcollector
SiO2 subcollector
P+ base
SiO2
P+ extrinsic base
N+ extrinsic base
S.I. substrate
N+ subcollector
SiO2 subcollector
P+ base
P+
N+
Base metal
SiO2
P+
N+
Base metal
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University of CaliforniaSanta Barbara Yingda Dong
Polycrystalline Base Contact in InP HBTs
5) Regrow emitter
S.I. substrate
N+ subcollector
SiO2 N- collector
P+ base
SiO2
P+
N+
Base metal
P+
N+
Base metal
Emitter
Emitter contact metal
CollectorMetal
Collector Metal
n+/p+ interface Is it rectifying or ohmic?
If ohmic, is the interfacial
contact resistivity low
enough?
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University of CaliforniaSanta Barbara Yingda Dong
P+ GaSb / N+ InAs Heterostructure
We propose to use p+ GaSb capped with n+ InAs as the extrinsic base.
EC
EV
P+ GaSb
N+ InAs EC
EV
Ef
InAs-GaSb heterostructure forms a
broken-gap band lineup
Mobile charge carriers tunnel between
the p-type GaSb’s valence band and
the neighboring n-type InAs’s
conduction band ohmic p-n junction
![Page 9: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/9.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Early Interests in InAs(n)/GaSb(p) Material System
InAs(n)/GaSb(p) heterostructure has been studied in 1990s with focuses on:
Applied Bias
Cur
rent
Den
sity Negative differential resistance (NDR)
Application in high frequency tunneling
diodes
1x105 A/cm2
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University of CaliforniaSanta Barbara Yingda Dong
Focus of This Work
The contact resistivity across the InAs(n)/GaSb(p) interface at
relatively low current density (<104 A/cm2).
(No NDR at low current density)
The dependence of contact resistivity on the doping
concentration in InAs and GaSb layers.
![Page 11: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/11.jpg)
University of CaliforniaSanta Barbara Yingda Dong
MBE Growth of Test Structures
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
1000Å n+ InAs
Carbon doped
Silicon doped
Samples grown in a Gen II
system
Sb source valved and
cracked
CBr4 delivered through high
vacuum leak valve
Layer structure designed
for InP HBT’s extrinsic
base for processing
reasons, total thickness
constrained
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University of CaliforniaSanta Barbara Yingda Dong
Measurement of Interfacial Contact Resistivity
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
1000Å n+ InAs
1) Transmission line patterns defined, Ti/Pt/Au contact metal deposited and lifted-off.
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University of CaliforniaSanta Barbara Yingda Dong
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
1000Å n+ InAs
2) Mesa defined to limit the current flow.
Measurement of Interfacial Contact Resistivity
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University of CaliforniaSanta Barbara Yingda Dong
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
1000Å n+ InAs
3) Contact resistivity between metal and n+ InAs layer measured.
Measurement of Interfacial Contact Resistivity
![Page 15: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/15.jpg)
University of CaliforniaSanta Barbara Yingda Dong
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
1000Å n+ InAs
0 2 4 6 8 10 12 14 160.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
R=0.09+0.24LR
sh=24 Ohm/Square
RC=1.0E-8 Ohmcm2
R (
Ohm
)
Gap Spacing (m)
Y Axis intercept = Contact resistance between metal and InAs
Measurement of Interfacial Contact Resistivity
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University of CaliforniaSanta Barbara Yingda Dong
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
n+InAs
n+InAs
n+InAs
n+InAs
4) Top InGaAs layer selectively etched
Measurement of Interfacial Contact Resistivity
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University of CaliforniaSanta Barbara Yingda Dong
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
n+InAs
n+InAs
n+InAs
n+InAs
0 5 10 15 20 25 300
10
20
30
40
50
60
70
R=2.3+2.16LR
sh=216 Ohm/Square
R (
ohm
)Gap Spacing (m)
Y Axis intercept = Contact resistance between metal and InAs + contact resistance between InAs and GaSb
Measurement of Interfacial Contact Resistivity
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University of CaliforniaSanta Barbara Yingda Dong
Contact Resistivity’s dependence on p-type GaSb layer’s doping
2x1019 3x1019 4x1019 5x1019 6x1019 7x1019
5.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
Si doping in InAs layer: 1x1017cm-3
InA
s-G
aSb
Inte
rfac
e C
onta
ct R
esis
tivity
(-
cm2 )
Carbon Doping Density in GaSb Layer (cm-3)
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
n+InAs
n+InAs
n+InAs
n+InAs
Silicon doping in n-type InAs layer
fixed at 1x1017cm-3
Carbon doping in p-type GaSb
varied
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University of CaliforniaSanta Barbara Yingda Dong
Contact Resistivity’s dependence on n-type InAs layer’s doping
S.I. InP
400Å p+ GaAs0.51Sb0.49
500Å p+ Grading from GaAs0.51As0.49
100Å p+ GaSb
n+InAs
n+InAs
n+InAs
n+InAs
Carbon doping in p-type GaSb layer
fixed at 4x1019cm-3 and 7x1019cm-3.
Silicon doping in p-type GaSb
varied.
1017 1018 1019 10202.0x10-7
4.0x10-7
6.0x10-7
8.0x10-7
1.0x10-6
1.2x10-6
1.4x10-6
1.6x10-6
1.8x10-6
2.0x10-6
C doping in GaSb layer: 4x1019cm-3
C doping in GaSb layer: 7x1019cm-3
InA
s-G
aSb
Inte
rfac
e C
onta
ct R
esis
tivity
(-
cm2 )
Silicon Doping Density in InAs Layer (cm-3)
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University of CaliforniaSanta Barbara Yingda Dong
Resonant Enhancement of Current Density
EC
EV
EC
EV
InAs/GaSb
EC
EV
EC
EV
InAs/GaSb/AlSb/GaSb
Formation of a quantum well layer
between the InAs/GaSb interface and
an AlSb barrier resonant
enhancement of the current density
For the single InAs/GaSb interface,
reflection occurs due to imperfect
coupling of InAs conduction-band
states and GaSb valence-band
states
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University of CaliforniaSanta Barbara Yingda Dong
Experiment Result
EC
EV
EC
EV
InAs/GaSb
EC
EV
EC
EV
InAs/GaSb/AlSb/GaSb
Si: 1x1017 cm-3C: 7x1019 cm-3
Si: 1x1017 cm-3C: 7x1019 cm-3
12Å AlSb
Contact resistivity: 6.0x10-7 -cm2
Contact resistivity: 5.4x10-7 - cm2
![Page 22: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/22.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Comparison with metal on p+ InGaAs
Doping Density of p-GaSb (cm-3)
Doping Density of n-InAs (cm-3)
Contact Resistivity (Ω-cm2)
2x1019 1x1017 2.8x10-6
2x1019 6x1017 3.0x10-6
4x1019 1x1017 1.3x10-6
4x1019 1x1019 1.6x10-6
4x1019 5x1019 9.0x10-7
7x1019 1x1017 6.0x10-7
7x1019 1x1019 8.2x10-7
7x1019 5x1019 4.2x10-7
Lowest interfacial contact
resistivity obtained: ~ 4x10-7 -cm2
Contact resistivity of metal on p+
InGaAs: ~1x10-6 -cm2
![Page 23: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/23.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Questions Answered
S.I. substrate
N+ subcollector
SiO2 N- collector
P+ base
SiO2
P+
N+
Base metal
P+
N+
Base metal
Emitter
Emitter contact metal
CollectorMetal
Collector Metal
n+/p+ interface
Is it rectifying or ohmic? -- YES
If ohmic, is the interfacial contact
resistivity low enough? -- YES
![Page 24: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/24.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Conclusions
Propose to use InAs(n)/GaSb(P) as extrinsic
base of InP HBT
Investigate the contact resistivity between
InAs(n)/GaSb(p) interface and its dependence
on doping densities on both sides of the
heterojunction.
Compare the InAs(n)/GaSb(p) interfacial contact
resistivity with that of metal on p+ InGaAs.
![Page 25: Characterization of Contact Resistivity on InAs/GaSb Interface](https://reader035.fdocuments.us/reader035/viewer/2022062407/56812c68550346895d91004c/html5/thumbnails/25.jpg)
University of CaliforniaSanta Barbara Yingda Dong
Acknowledgement
This work was supported by the DARPA—TFAST program