regrown ohmic contacts to in x ga 1-x as approaching the quantum conductivity limit
Post on 14-Jan-2016
30 Views
Preview:
DESCRIPTION
TRANSCRIPT
Regrown Ohmic Contacts to
InxGa1-xAs Approaching the
Quantum Conductivity Limit
Jeremy J. M. Law,a,b Andy D . Carter,a Sanghoon Lee,a Arthur C. Gossard,a,b and Mark J. W. Rodwella
Device Research Conference, June 19, 2012
a) Department of Electrical and Computer Engineering, University of California, Santa Barbara
b) Materials Department, University of California, Santa Barbara
Outline
•Motivation
•Ballistic FET Current and TLM Quantum Conductance
•Process Flow
•Sample Structures
− Regrowth TLM (RGTLM)
− Transmission Line Measurement (TLM)
•Results
− Metal-semiconductor (TLM)
− Metal-semiconductor and semiconductor-channel (RGTLM)
•Theory Comparison
•Conclusion
2
Motivation
• Two interfaces of interest– Metal–regrowth interface
– Regrowth–channel interface
• Sheet resistance of regrowth
• Sheet resistance of ungated region
• Must ascertain contribution to overall access resistance from all of above
Source/Drain–Channel
Metal–Source/DrainUngated Channel
Unmetalized Source/Drain
3
FET Ballistic Current = TLM Quantum Conductance • Fundamental limits to contact resistance to a two-dimensional channel?• Quantum limited contact resistance1, 2 equivalent to ballistic transconductance
4 1 P. M. Solomon et al., IEDM Tech. Dig., 1989, p. 405; 2 J Guo et al., IEEE Elec. Dev. Lett. 33, 525 (2012).
Regrowth TLM (RGTLM) Process Flow
Epi growth Dummy Pillar Definition Regrowth
Planarization Isolation S/D Metalization
• Understand source (regrowth) to channel interface• Rudimentary process flow• Approximates FET structure and process flow
– Independent of high-k properties• Four-point Kelvin measurement
5
TLM Process Flow
Epi growth Regrowth
Isolation S/D Metalization
6
• Understand metal to source (regrowth) interface
• Rudimentary process flow
• Can be done on same die as RGTLM
• Four-point Kelvin measurement
Sample Structures: TLM
7
InAs RG on d–doped 25 nm In0.53Ga0.47As channel
InAs RG on 100 nm n+ In0.53Ga0.47As channel
InAs RG on d–doped 15 nm InAs channel
In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel
TLM Results
8
InAs RG on d–doped 25 nm In0.53Ga0.47As channel
InAs RG on 100 nm n+ In0.53Ga0.47As channel
InAs RG on d–doped 15 nm InAs channel
In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel
Slope: 23.8 W; Intercept/2: 2.1 W–mm
Slope: 19.3 W; Intercept/2: 3.0 W–mm Slope: 11.3 W; Intercept/2: 3.0 W–mm
Slope: 7.4 W; Intercept/2: 4.6 W–mm
Sample Structures: RGTLM
9
InAs RG on d–doped 25 nm In0.53Ga0.47As channel
InAs RG on 100 nm n+ In0.53Ga0.47As channel
InAs RG on d–doped 15 nm InAs channel
In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel
Regrowth TLM Results
10
InAs RG on d–doped 25 nm In0.53Ga0.47As channel
InAs RG on 100 nm n+ In0.53Ga0.47As channel
InAs RG on d–doped 15 nm InAs channel
In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel
Slope: 540 W; Intercept/2: 120.8 W–mm
Slope: 32 W; Intercept/2: 55.6 W–mm
Slope: 269 W; Intercept/2: 68.2 W–mm Slope: 15 W; Intercept/2: 12.7 W–mm
Results Summary
N+ Regrowth
Composition InAs InAs InAs In0.53Ga0.47As → InAs
Thickness 60 nm 60 nm 60 nm 60 nm
Doping 5-10×1019 cm-3 5-10×1019 cm-3 5-10×1019 cm-3 5-10×1019 cm-3
Sheet Resistivity 23.8 W 7.4 W 19.3 W 11.3 W
Channel
Composition In0.53Ga0.47As In0.53Ga0.47As InAs In0.53Ga0.47As
Thickness 25 nm 100 nm 15 nm 100 nm
Doping 9×1012 cm-2 3-5×1019 cm-3 9×1012 cm-2 3-5×1019 cm-3
Sheet Resistivity 540 W 32 W 269 W 15 W
Access Resistivity 120.8 -W mm 55.6 -W mm 68.2 -W mm 12.7 -W mmMetal/Regrowth Contact Resistivity 2.1 -W mm
0.2 -W mm24.6 -W mm1.5 -W mm2
3.0 -W mm0.4 -W mm2
3.0 -W mm0.8 -W mm2
• Contact resistance to thin channels (small ns) limited by quantum conductance
• Low contact resistance of 12.7 W–mm (11.1 W–mm2)• Contact resistance low ns channels 136.4 W–mm close to theoretical 80 W–
mm
Conclusion
• Ballistic FET current equivalent to quantum conductance of TLM
• Should not add to FET contact resistance
• Material independent, i.e. true for all semiconductor materials
• Metal–regrowth contact resistance is small portion of overall Rc
– ~ 3.0 W–mm (1.0 W–mm2)
• Regrown ohmic contacts (136 W–mm) within a factor of 2 of theoretical 80 W–mm
• 12.7 W–mm (11.1 W–mm2) is true measure of interface properties– This includes regrowth to channel and metal to regrowth
12
Backup slides
MBE Regrowth by Migration Enhance Epitaxy (MEE)
InAs Quasi MEE
In, As, and Si shutters open As shutter open
InGaAs Quasi MEE
In, Ga, As, and Si shutters open As shutter open
14
MBE Regrowth: Close to 2-D Quantum conductivity Limit:
channel. D-2in minimum band conduction torelative taken Energies
left right to direction; in moving charge :States Blue
right left to direction; in moving charge :States Red
x
x
*111,1s11
*111
*11
21
*11
11,s1
2*21,
/2)3/4( :current Leftward
/2)3/4()3/4( :elocityelectron v leftwardMean
/22/ :Velocity Fermi moving-Leftward
:states moving-leftin density Charge
2/ :states ofdensity 2D onalUnidirecti
mqVVcvJ
mqVvv
mqVvvmqVE
Vc
gmqc
ffdos
ff
fffff
fdos
dos
2/32
2/31*1,
2
3
4 :current Total ffdos VV
m
qcJ
2/1
*1, 2
32
3
4/ty Conductivi fdosf V
m
qcVJG
seigenstate verticaland ysover valle summingby foundty conductivi Total
.degeneracyspin including 2 2/1
,2/3
2/12
valleysvalley nq
G
effect by this limited being are tsmeasuremen resistanceregrowth UCSB
15
top related