1. Eliminating Gate-Voltage Hysteresis in
Suspended Single-Walled Carbon
Nanotube Field-Effect Transistors
Ajay Subramanian, Takushi Uda, and Y.K. Kato

2. Outline
Introduction
◦ Single-Walled Carbon Nanotubes
◦ Field-Effect Transistor Architecture and Synthesis
◦ What is Gate-Voltage Hysteresis?
Measurements and Processes
◦ Optical Measurement Setup
◦ Measurements and Results
◦ Photoluminescence vs Gate-Voltage
◦ Pressure Dependence and Air Recovery
◦ Environment Effects
Conclusions and Future Work

3. Single-Walled Carbon Nanotubes
(SWCNT)
• SWCNTs have unique mechanical and electronic properties that
make them attractive for innovative new science
• Notably, different chiralities of nanotubes correspond to metallic
and semiconducting electronic properties.
• SWCNTs have small dimension and direct band gap: potential
application in optoelectronics

4. Field-Effect Transistor Architecture
• FET devices take advantage of these
properties; trench architecture allows
for large photoluminescence.
• Si back gate allows for electrostatic
doping of charge carriers

5. What is hysteresis?
-Environmental conditions that affect
the gate dependence of various
properties
-Adsorbed water or hydroxyl groups
-How do we eliminate it?
Semiconducting SWCNT
-6 -4 -2 0 2 4 6
0
50n
100n
150n
Draincurrent(A)
Gate voltage (V)
-6 -4 -2 0 2 4 6
0.0
1.0µ
2.0µ
3.0µ
Draincurrent(A)
Gate voltage (V)
Metallic SWCNT
Nano lett. 3, 193 (2003), W. Kim et al

6. Outline
Introduction
◦ Single-Walled Carbon Nanotubes
◦ Field-Effect Transistor Architecture and Synthesis
◦ What is Gate-Voltage Hysteresis?
Measurements and Processes
◦ Optical Measurement Setup
◦ Measurements and Results
◦ Photoluminescence vs Gate-Voltage
◦ Pressure Dependence and Air Recovery
◦ Environment Effects
Conclusions and Future Work

7. The Vacuum Box
Modified Optical Microscopy Cryostat
◦ Create PCB
◦ Wire the inside of the cryostat
◦ Create wire connection from voltage box to cryostat
◦ Mount in the optical setup

8. Optical Setup
Lens
Shutter
Pinhole
Steering
Mirror
Lens pair
1D Stage
Objective lens
Cryostat
Long-pass filter
PL
Detector

9. Outline
Introduction
◦ Single-Walled Carbon Nanotubes
◦ Field-Effect Transistor Architecture and Synthesis
◦ What is Gate-Voltage Hysteresis?
Measurements and Processes
◦ Optical Measurement Setup
◦ Measurements and Results
◦ Photoluminescence vs Gate-Voltage
◦ Pressure Dependence and Air Recovery
◦ Environment Effects
Conclusions and Future Work

10. Photoluminescence vs. Voltage
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
-5 -4 -3 -2 -1 0 1 2 3 4 5
Gate-Voltage
(V)
NormalizedPL(arb.units)
In Air In Vacuum
• In air: clear hysteresis defined by two distinct peaks , quenching values
• In vacuum, PL quenches normally; measurements done on (9,7) SWCNT

11. Pressure Dependence
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
1.0e3 mbar (Air) 3.0 mbar
6.3e-6 mbar1.4e-3 mbar
1000 100 10 1 0.1 0.01 1E-3 1E-4 1E-5 1E-6
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Hysteresis(V)
Pressure (mbar)
• In situ pressure dependence measurements done with TurboPump
• Method: Z, 2D, reflectivity position scans. Then, X PL scan, followed by PLV

12. Air Recovery
-5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPL
-5 -4 -3 -2 -1 0 1 2 3 4 5
• Hysteresis recovers after exposure to air; we observe clear increase over time
• How can we control it?

13. N2 Environment
0 200 400 600 800 1000 1200 1400
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
Hysteresis(V)
Time (minutes)
N2
Exposure
Air Exposure

14. N2 Environment
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedPLIntensity
Gate-Voltage (V)
60 min. N2 5910 min. (4 days) N2

15. Conclusions, Challenges, Future Work
• Clear elimination of hysteresis in PLV in the new vacuum box setup
• Isolated cause of hysteresis to adsorbed atmospheric molecules, e.g.
water
What’s next?
• New gate-voltage dependence measurements
• Possible giant band gap renormalization