Optoelectronics with Carbon Nanotubes

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numerical aperture of the objective lens, we are collecting in the solid angle that covers about 4% at 90-degree angle to the tube direction. Figure V - 12 clearly shows that the electroluminescence is linearly polarized in such a way that intensity maxima are obtained if the transmission direction of the polarizer is aligned with the CNT direction. The cosine-squared fits reveal intensity ratios Imax/Imin (i.e. ratios with polarizer at 0°/180° over 90°/270° in Figure V-12) close to 3.5. The degree of polarization is of the same order as those obtained in electroluminescence 73, 87 , photoluminescence and Raman 137 as well as photoconductivity measurements 135, 136 performed on single nanotubes, demonstrating the extraordinary level of alignment in the CNT film. We did not observe any statistically significant difference in the degree of light polarization when the CNT film diode is operated in the reverse mode (see Figure V-12 (b)). This is not unexpected, since the polarization dependence of the electroluminescence measurement reflects the nature of exciton recombination rather than exciton creation. Since we do not observe light emission from the CNT-metal-contacts that are covered by the metallic gates (see Figure V-6 (d)), the polarization dependence in both forward and reverse mode reflects solely the alignment of the CNTs in the “active area” between the split gates (see Figure 1). (a) (b) Figure V-12. Polarization dependence of the electroluminescence intensity from a CNT thin film diode in the (a) forward mode and (b) reverse mode (VDS=10V for both (a) and (b)) for two different split gate settings VTG1/VTG2 (solid symbols: 105
experiment, solid line: cosine squared fit). Imax/Imin is the ratio of the intensity maximum to the minimum from the fit. The overall intensity is much higher for the reverse mode (note the scale) because of the high current at the same VDS (e.g. Figure V-8 (a) inset). The total intensity difference as a function of the top gate is smaller for the reverse mode, in agreement with Figure V-8 (a). The CNTs forming the film are aligned along the 0 o – 180 o marks. 6. Conclusions We have realized polarized light-emitting diodes from highly aligned, separated semiconducting carbon nanotube films that show tunable light generation efficiencies and threshold-less light emission characteristics. Additional improvement in device performance can be expected by superior enrichment of the solution-processed CNT. Reduction of metallic tubes in the raw material will enable shorter device channels for better transport, or even eliminate percolation altogether, which means one can create devices equivalent to single-tube CNT LEDs in parallel. Also, avoidance of excess chemical treatment and processing will decrease the defect concentration of the CNT material and help to further improve the light generation efficiency. 106
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Stony Brook University The official
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Stony Brook University The Graduate
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diodes nonetheless show a rectifyin
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Table of Contents Abstract ........
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Chapter I List of Figures Figure
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Figure ‎V-3 Source-drain electric
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My parents have been steadfast supp
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This work explores both fundamental
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In fact, we typically have no knowl
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(a) (b) Figure I-2 (a) Energy dispe
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(a) (b) metallic Figure I-4. One-di
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optical absorption peaks for differ
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elax rapidly to lower non-radiative
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The disorder-induced band (D-band)
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The saturation limit for semiconduc
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(a) (b) Figure I-7. (a) A schematic
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assisted tunneling through Schottky
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majority carriers that gain enough
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conventional ambipolar emission. Th
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on quartz, which remains a signific
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Chapter II Methods 1. Materials One
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diameter (< 2 nm) SWNTs at IBM T. J
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devices were annealed in vacuum at
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3. Experimental set-up The optical
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off wavelengths of 2150 nm, 2000 nm
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Chapter III Unipolar, High-Bias Emi
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Figure III-1. Semi-log plot of drai
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wetting with CNTs 57 and a relative
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Figure III-4. (Main panel) Electrol
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By plotting the current as a functi
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phonon temperature in broadening. S
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found multiple tubes bound together
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where i is the phonon mode, Tsub is
Page 67 and 68: The main panel of Figure III-10 sho
Page 69 and 70: the effect following Perebeinos’
Page 71 and 72: the optical phonon population is no
Page 73 and 74: (a) Figure III-13. (a) Spectra from
Page 75 and 76: DOP = I║ / (I┴ + I║) = 0.77.
Page 77 and 78: inding energy for perpendicular exc
Page 79 and 80: 3. Conclusions We have examined the
Page 81 and 82: In a split-gate scheme, a new level
Page 83 and 84: 3. Electroluminescence mechanism an
Page 85 and 86: After calibrating our detection sys
Page 87 and 88: (a) (b) Figure IV-3. Electrolumines
Page 89 and 90: observed by increasing the VGS valu
Page 91 and 92: We claimed in Chapter III that in t
Page 93 and 94: Let us finally comment on the effic
Page 95 and 96: Chapter V The Polarized Carbon Nano
Page 97 and 98: (a) (b) Figure V-1. (a) SEM image o
Page 99 and 100: oth electrons and holes can be inje
Page 101 and 102: In the reverse direction (i.e., neg
Page 103 and 104: 4. Electroluminescence characterist
Page 105 and 106: and drain pads (marked “S” and
Page 107 and 108: (a) (b) Figure V-8. (a) EL intensit
Page 109 and 110: We attribute the observation of the
Page 111 and 112: (a) (b) (c) Figure V-9. Electrolumi
Page 113 and 114: measurements (i.e. additional chemi
Page 115 and 116: (a) (b) Figure V-10. Full-width at
Page 117: mechanisms are the same for differe
Page 121 and 122: emission observed at higher current
Page 123 and 124: Bibliography 1. Avouris, P.; Chen,
Page 125 and 126: 30. Miyauchi, Y.; Maruyama, S., Ide
Page 127 and 128: 56. Chen, Z.; Appenzeller, J.; Knoc
Page 129 and 130: 85. Marty, L.; Adam, E.; Albert, L.
Page 131 and 132: 112. Steiner, M.; Freitag, M.; Pere
Page 133 and 134: 140. Grüneis, A.; Saito, R.; Samso
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Optoelectronics with Carbon Nanotubes

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