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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)
x 0
Current annealed fiberIodine doped fiber
Annealed fiberIodine doped fiber
x 0
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
Phot
ovol
tage
(mV)
0
0.45
0.9
1.35
1.8
Laser Power (mW)0 2.75 5.5 8.25 11
I2 doped 20micron, 660nmAs Spun 20micron, 660nmS Doped 20um, 660nm
Results
Polarization Dependence
-60 -40 -20 0 20 40 60 80 100
-4
-2
0
2
4
ΔI
ΔV
Under illumination
Volta
ge (m
V)
Current (µA)
Without illumination
Laser excitation Heat exchange by gas
• Seebeck effect is generated from the heat produced by laser excitation
dTdVS −= ∫ ⋅−=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/Vm
ax
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/Vm
ax
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