Optoelectronics with Carbon Nanotubes
Optoelectronics with Carbon Nanotubes Optoelectronics with Carbon Nanotubes
Figure V-2. (a) Schematic illustration and (b) scanning electron microscope image of CNT film diodes with split top gates (TG1 and TG2). The white scale bar on lower left is 5 μm long. 3. Transport characteristics of the CNT film diode As we saw in the case of the single-tube CNT diode, good transport behavior is critical for efficient light emission. This is not surprising since the radiative recombination rate of excitons in CNTs is much smaller than the non-radiative recombination rate. Here, we discuss electronic transport of CNT film devices with top-split gate to confirm that they do indeed behave as diodes. (a) (b) The electrical transfer characteristics of two devices with different channel lengths (4 μm and 6 μm) are shown in Figure V-3 (a) and (b). We see that the fundamental requirement for CNT diode construction, namely the ambipolar behavior upon gate-sweeping, is satisfied in these devices. The almost symmetric, ambipolar transfer characteristics of the devices indicate that 85
oth electrons and holes can be injected into the channel with similar efficiencies. We also see that there is much less noise in current compared to single-tube devices under similar conditions (compare to Figure III-3, for example), because multiple channels cancel fluctuations from individual tubes. The sheet resistances was found to be around 1 MΩ/□ and the on/off current ratios is about 100 for VDS = 1 V. The performance is somewhat degraded both in conductivity and in the on/off ratio compared to the global bottom-gated devices in Ref. 99. This is partly due to the fact that the global gate covers the entire device channel while our split gates have only partial channel coverage. More significantly, we re-used the same material, and re-processing the same film multiple times degrades the performance by introducing defects and impurities. It has also been observed in single-tube devices that applying high bias seems to damage CNTs. The D-line (i.e. defect induced; see Introduction) intensity from Raman measurement in a single tube increases after we applied high bias/current repeatedly. In addition, as described in Chapter IV, we have observed that the defect-bound E11 peak developed after measurements in a single CNT p-n junction. (a) (b) Figure V-3. (a, b) Source-drain electrical current transfer as a function of the top-gate voltage measured for CNT film diodes with a channel length (a) LC=4 μm and (b) LC=6 μm, respectively, where VTG = VTG1 = VTG2. VTG was swept in both directions, resulting in hysteresis that is typical in on-substrate CNT devices. The bottom gate was floating. After Ref. 152. 86
- Page 47 and 48: 3. Experimental set-up The optical
- Page 49 and 50: off wavelengths of 2150 nm, 2000 nm
- Page 51 and 52: Chapter III Unipolar, High-Bias Emi
- Page 53 and 54: Figure III-1. Semi-log plot of drai
- Page 55 and 56: wetting with CNTs 57 and a relative
- Page 57 and 58: Figure III-4. (Main panel) Electrol
- Page 59 and 60: By plotting the current as a functi
- Page 61 and 62: phonon temperature in broadening. S
- Page 63 and 64: found multiple tubes bound together
- Page 65 and 66: 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: (a) (b) Figure V-1. (a) SEM image o
- 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 and 118: mechanisms are the same for differe
- Page 119 and 120: experiment, solid line: cosine squa
- 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
oth electrons and holes can be injected into the channel <strong>with</strong> similar efficiencies. We also see<br />
that there is much less noise in current compared to single-tube devices under similar conditions<br />
(compare to Figure III-3, for example), because multiple channels cancel fluctuations from<br />
individual tubes. The sheet resistances was found to be around 1 MΩ/□ and the on/off current<br />
ratios is about 100 for VDS = 1 V. The performance is somewhat degraded both in conductivity<br />
and in the on/off ratio compared to the global bottom-gated devices in Ref. 99. This is partly due<br />
to the fact that the global gate covers the entire device channel while our split gates have only<br />
partial channel coverage. More significantly, we re-used the same material, and re-processing<br />
the same film multiple times degrades the performance by introducing defects and impurities. It<br />
has also been observed in single-tube devices that applying high bias seems to damage CNTs.<br />
The D-line (i.e. defect induced; see Introduction) intensity from Raman measurement in a single<br />
tube increases after we applied high bias/current repeatedly. In addition, as described in Chapter<br />
IV, we have observed that the defect-bound E11 peak developed after measurements in a single<br />
CNT p-n junction.<br />
(a) (b)<br />
Figure V-3. (a, b) Source-drain electrical current transfer as a function of the top-gate<br />
voltage measured for CNT film diodes <strong>with</strong> a channel length (a) LC=4 μm and (b)<br />
LC=6 μm, respectively, where VTG = VTG1 = VTG2. VTG was swept in both directions,<br />
resulting in hysteresis that is typical in on-substrate CNT devices. The bottom gate<br />
was floating. After Ref. 152.<br />
86
Change language