Nonradiative recombination of excitons in carbon nanotubes mediated by free charge carriers

Kinder, Jesse M.; Mele, Eugene J.

doi:10.1103/physrevb.78.155429

Cited by 31 publications

(44 citation statements)

References 22 publications

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“…[23][24][25][26][27][28][29][30][31][32] Drastic changes in the absorption and photoluminescence due to the bright excitons have been observed as the doped hole density increases. 24,28 Because of the conservation of energy and momentum, charge carriers can interact effectively with dark excitons, 33 and carrier doping could modify the optical responses of SWCNTs through these dark excitons. Moreover, positive trions (positively charged excitons) have recently been discovered in holedoped SWCNTs at room temperature.…”

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Trion formation and recombination dynamics in hole-doped single-walled carbon nanotubes

Nishihara

Yamada

Okano

et al. 2013

Applied Physics Letters

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We studied the trion (charged exciton) formation and recombination dynamics in hole-doped (7,5) single-walled carbon nanotubes (SWCNTs) by performing femtosecond transient absorption spectroscopy. The doping of SWCNTs with holes leads to a fast decay component from an exciton to a trion, and the trion decays with a lifetime of a few picoseconds. The experimental results can be explained by a quantized model accounting for the dark exciton and trion states and the hole number distribution in a SWCNT. Our findings show that the optical responses of SWCNTs can be manipulated by doping of SWCNTs with a small number of holes.

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Trion formation and recombination dynamics in hole-doped single-walled carbon nanotubes

Nishihara

Yamada

Okano

et al. 2013

Applied Physics Letters

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“…To simulate the changes in the PL efficiency, we calculate γ 0 /[γ 0 + γ d (ρ)] where γ 0 = 0.01 ps −1 is the exciton relaxation rate in the absence of doping 22 and γ d (ρ) is the doping-induced relaxation rate. Assuming γ d proportional to ρ, 9,10,23 we have performed a least-squares fit to normalized data with γ d = αρ where α is a proportionality constant used as a fitting parameter ( Fig. 4, blue curve).…”

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Gate-induced blueshift and quenching of photoluminescence in suspended single-walled carbon nanotubes

et al. 2011

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Gate-voltage effects on photoluminescence spectra of suspended single-walled carbon nanotubes are investigated. Photoluminescence microscopy and excitation spectroscopy are used to identify individual nanotubes and to determine their chiralities. Under an application of gate voltage, we observe slight blueshifts in the emission energy and strong quenching of photoluminescence. The blueshifts are similar for different chiralities investigated, suggesting extrinsic mechanisms. In addition, we find that the photoluminescence intensity quenches exponentially with gate voltage. PACS numbers: 78.67.Ch, 85.35.Kt, Understanding of electric-field effects on optical emission from single-walled carbon nanotubes (SWCNTs) is a key to the development of carbon-based nanoscale optoelectronics. 1 It has been shown that electric fields can drive light emission in SWCNTs. 2,3 In comparison, photoluminescence (PL) is quenched by an application of electric fields. Micelle-encapsulated SWCNTs show a reduction of PL intensity by electric fields along the tube axis. 4 Similar quenching occurs in suspended nanotubes within field-effect transistor (FET) structures. 5-7 Such strong quenching of PL has made it difficult to unambiguously resolve shifts in the emission spectra, in contrast to absorption measurements where redshifts due to the Stark effect 8 and doping-induced screening 6 have been observed. Detailed PL spectroscopy on nanotubes with determined chirality would help clarify the role of these effects on optical emission.Here we report on gate-voltage dependence of PL spectra in individual suspended SWCNTs. As-grown nanotubes within FET structures are identified by PL imaging using a laser scanning confocal microscope. Excitation spectroscopy is used to determine their chirality, and PL spectra are collected as a function of gate voltage. Surprisingly, we find that the emission blueshifts when the gate voltages are applied. Furthermore, the PL intensity decreases exponentially with gate voltage, and we find that a model assuming doping-induced exciton relaxation proportional to carrier density 9,10 cannot account for all of the quenching observed.The suspended nanotube FETs [ Fig. 1(a)] are fabricated on p-type Si substrates with 100-nm-thick oxide. We begin by etching 1-µm wide trenches with a depth of ∼ 5 µm. The wafer is then annealed at 900 • C in oxygen for an hour to form an oxide layer inside the trenches. 1-nm Ti and 15-nm Pt are deposited for source and drain contacts, and then catalyst areas are defined on the drain electrodes. Co acetate and fumed silica are dissolved in ethanol, and deposited on the wafer. Finally, carbon nanotubes are grown by chemical vapor deposition using ethanol as a carbon source. 11 Typical device characteristics are shown in Fig. 1(b), and we note that these devices show hysteresis due to water adsorption. 12 PL spectra are collected with a home-built laser scanning confocal microscope. 13 An output of a continuouswave Ti:sapphire laser is focused onto the sample with an objective lens, and a...

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“…21 At low exciton densities, possibilities include nonradiative recombination mediated by phonons or free electrons and holes. 22,23 Depending on the decay channel, the peak conductivity of the S 11 exciton may not be uniform across a nanotube sample, and may differ significantly from 8 e 2 /h. No experimental data are available for this transition.…”

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confidence: 99%

Uniform peak optical conductivity in single-walled carbon nanotubes

2011

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Recent Rayleigh scattering measurements show that all single-walled carbon nanotubes have a peak optical conductivity of approximately 8 e 2 /h, independent of radius, chiral angle, or whether the nanotube is semiconducting or metallic [D. Y. Joh et al., Nat. Nanotechnol. 6, 51 (2011)]. We show that this uniform peak conductivity is a consequence of the relativistic band structure and strength of the Coulomb interaction in carbon nanotubes. We also show that a simple exciton model accurately describes the general phenomenology and the numerical value of the peak optical conductivity. Our work illustrates the need for careful treatment of relaxation mechanisms in modeling the optoelectronic properties of carbon nanotubes.

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Nonradiative recombination of excitons in carbon nanotubes mediated by free charge carriers

Cited by 31 publications

References 22 publications

Trion formation and recombination dynamics in hole-doped single-walled carbon nanotubes

Trion formation and recombination dynamics in hole-doped single-walled carbon nanotubes

Gate-induced blueshift and quenching of photoluminescence in suspended single-walled carbon nanotubes

Uniform peak optical conductivity in single-walled carbon nanotubes

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