Optoelectronics with Carbon Nanotubes
Optoelectronics with Carbon Nanotubes Optoelectronics with Carbon Nanotubes
Figure III-2. Source-Drain sweep showing saturation at the current level ~1 μA. The device is mostly ambipolar with a stronger n-branch (inset). The saturation behavior is most clearly demonstrated when the device is in the “on” state (black squares). It should be noted that the gate voltage dependence tends to change when the device is subjected to high-bias. Most notably, most of them change from p-type to n-type after passing a high current (Figure III-3). Although this phenomenon was not systematically investigated, the change typically lasts for days to weeks in vacuum (~10 -6 Torr) and gradually reverts to p-type, suggesting that it is affected by adsorbed gas molecules from the environment. Ohno et al. reported a similar change in transport from p-type to ambipolar after heating at 100 ˚C in vacuum for 24 hours 105 . They attribute this change to the elimination of adsorbed oxygen and the resulting change in interfacial dipole at the contact, which makes the Fermi level align mid-gap. This is also consistent with previous observations where charge injection occurs either directly into the traps in substrate or into the water molecules surrounding the nanotube and the SiO2 surface 106-108 . In the current study, Pd was used as a contact throughout (with a very thin layer of Ti for adhesion and capped with Au to facilitate electrical contact to the probes) because of its good 41
wetting with CNTs 57 and a relatively high melting point. The maximum current at a saturation gate voltage did not change significantly as a result of the change in VGS dependence. In addition, annealing by passing a high current makes the device more stable, so that the current characteristics are less noisy and more repeatable. Figure III-3 shows an example of the change from p-type to n-type FET as a result of passing a current close to 10 μA. Note that III-3 (a) corresponds to the same parameters as in Figure III-2, but from a different device. The n- branch in III-3 (a), i.e., the positive gate voltage side, shows higher current than in III-2, most likely because of the larger tube diameter (see caption). All our measurements at high biases were taken after a few rounds of high-bias (~10 μA) transport until the electric characteristics became stable from sweep to sweep. (a) (b) Figure III-3. Change in transport from predominantly p-type FET (a) to n-type FET (b). The sweep was conducted stepwise from -1 V to -7V as shown in (a), followed by the same in (b). This is a larger diameter tube as indicated by the metallic-like transport at VDS = -7 V, and by the electroluminescence spectra in which the E11 peak is not observable because it is outside the detection range (not shown). 42
- Page 3 and 4: Stony Brook University The Graduate
- Page 5 and 6: diodes nonetheless show a rectifyin
- Page 7 and 8: Table of Contents Abstract ........
- Page 9 and 10: Chapter I List of Figures Figure
- Page 11 and 12: Figure V-3 Source-drain electric
- Page 13 and 14: My parents have been steadfast supp
- Page 15 and 16: This work explores both fundamental
- Page 17 and 18: In fact, we typically have no knowl
- Page 19 and 20: (a) (b) Figure I-2 (a) Energy dispe
- Page 21 and 22: (a) (b) metallic Figure I-4. One-di
- Page 23 and 24: optical absorption peaks for differ
- Page 25 and 26: elax rapidly to lower non-radiative
- Page 27 and 28: The disorder-induced band (D-band)
- Page 29 and 30: The saturation limit for semiconduc
- Page 31 and 32: (a) (b) Figure I-7. (a) A schematic
- Page 33 and 34: assisted tunneling through Schottky
- Page 35 and 36: majority carriers that gain enough
- Page 37 and 38: conventional ambipolar emission. Th
- Page 39 and 40: on quartz, which remains a signific
- Page 41 and 42: Chapter II Methods 1. Materials One
- Page 43 and 44: diameter (< 2 nm) SWNTs at IBM T. J
- Page 45 and 46: devices were annealed in vacuum at
- 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: Figure III-1. Semi-log plot of drai
- 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 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
wetting <strong>with</strong> CNTs 57 and a relatively high melting point. The maximum current at a saturation<br />
gate voltage did not change significantly as a result of the change in VGS dependence.<br />
In addition, annealing by passing a high current makes the device more stable, so that the<br />
current characteristics are less noisy and more repeatable. Figure III-3 shows an example of the<br />
change from p-type to n-type FET as a result of passing a current close to 10 μA. Note that III-3<br />
(a) corresponds to the same parameters as in Figure III-2, but from a different device. The n-<br />
branch in III-3 (a), i.e., the positive gate voltage side, shows higher current than in III-2, most<br />
likely because of the larger tube diameter (see caption). All our measurements at high biases<br />
were taken after a few rounds of high-bias (~10 μA) transport until the electric characteristics<br />
became stable from sweep to sweep.<br />
(a) (b)<br />
Figure III-3. Change in transport from predominantly p-type FET (a) to n-type FET<br />
(b). The sweep was conducted stepwise from -1 V to -7V as shown in (a), followed<br />
by the same in (b). This is a larger diameter tube as indicated by the metallic-like<br />
transport at VDS = -7 V, and by the electroluminescence spectra in which the E11 peak<br />
is not observable because it is outside the detection range (not shown).<br />
42
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