1) Carbon nanotube fibers can be used as broadband photodetectors due to their mechanical strength, electrical conductivity, thermal conductivity, and ability to absorb light across a wide electromagnetic spectrum. 2) Two types of photodetectors were fabricated from the fibers: double-fiber devices using two interconnected fibers, and single-fiber devices using half of one fiber. 3) Testing showed the photodetectors generated a photovoltage in response to laser excitation due to the Seebeck effect from heat produced, and performance depended on factors like doping, wavelength, and position along the fiber.

1. Broadband Photodetector Based on Carbon Nanotube
Fibers
This material is based upon work supported by the National Science
Foundation under Grant No. EEC-0540832.
Simon Lee1, Xuan Wang2, Sébastien Nanot2, Xiaowei He2, Colin C. Young3, Dmitri E. Tsentalovich3, Matteo Pasquali3, and Junichiro Kono2
1Department of Biochemistry & Biophysics, Texas A&M University, College Station, Texas, USA
2Department of Electrical & Computer Engineering, Rice University, Houston, Texas, USA
3Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, USA
www.mirthecenter.org
Motivation
Why carbon nanotubes?
• Mechanical strength: strong covalent bonds
yet flexible
• Optical properties: sensitive to broadband
absorptions across a wide electromagnetic
spectra
• Electrical properties: can be metallic or a
semiconductor; high current-carrying
capacity; great electron mobility
Background
• Our fibers consist of well aligned and densely
packed carbon nanotubes [1]
• Fibers carry over their microscopic characteristics:
1. mechanically strong
and flexible
2. electrically conductive
3. thermally conductive
4. optically absorptive
within a broad band
of the electromagnetic
spectra
• The fibers optically absorb energy from a light
source, in this case a laser, generating a thermal
distribution across the length of the fiber.
Photodetector Fabrication
Two ways photodetecting devices were made:
1. Double-fiber photodetector:
interconnection between two
fibers creates a node
2. Single-fiber photodetector: use current
to anneal only half of the fiber.
(junction is continuous)
x0
Current annealed fiberIodine doped fiber
Annealed fiberIodine doped fiber
x0
Figure (a) corresponds to the double-fiber
photodetector with its interconnection,
magnified in Figure (b).
Series or parallel circuits can be created
by several identical devices to enhance
signal.
Doping Dependence Wavelength Dependence
Position Dependence
Conclusion & Future Plans
• The CNT fiber’s photodetecting ability is a result to its
photothermoelectric properties that are inherent to the
fibers.
• The wavelength dependent graphs require a
normalization by calculating the beam size.
• Polarization dependence should be able to be seen in the
single fiber devices due to the aligned nature of the
fiber.
• Seebeck coefficient depends on doping. Therefore, tests
are not limited to iodine doped samples. Other samples
such as sulfur-doped and potassium-doped samples
were created and tested.
(a)
(b)
References
[1] N. Behabtu,et al., “Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh
Conductivity”, Science 339 (2013) 182–186.
[2] X. He et al., “Photothermoelectric p-n Junction Photodetector with Intrinsic Broadband Polarimetry
Based on Macroscopic Carbon Nanotube Films”, ACS Nano, ASAP,Web (2013) DOI: 10.1021/nn402679u
Science 339.6116 (2013): 182-186
Photovoltage(mV)
0
0.45
0.9
1.35
1.8
Laser Power (mW)
0 2.75 5.5 8.25 11
I2 doped 20micron, 660nm
As Spun 20micron, 660nm
S Doped 20um, 660nm
Results
Polarization Dependence
-60 -40 -20 0 20 40 60 80 100
-4
-2
0
2
4
ΔI
ΔV
Under illumination
Voltage(mV)
Current (µA)
Without illumination
Laser excitationHeat exchange by gas
• Seebeck effect is generated from the heat
produced by laser excitation
dT
dV
S −= ∫ ⋅−=Δ
2
1
x
x
dTSV
ACS Nano, X. He et al.,
Because of the well aligned nature
of the CNT fibers, a polarization
dependence should be observed.
Polarization dependence has been
observed in CNT films [2]
V/Vmax
0
0.25
0.5
0.75
1
Position (mm)
-3 -2.3 -1.5 -0.8 0 0.8 1.5 2.3
As-Spun Current Annealed
V/Vmax
0
0.25
0.5
0.75
1
Position (mm)
-3 -2.3 -1.5 -0.8 0 0.8 1.5 2.3 3
As-Spun Annealed