Nonlinear photoluminescence properties of trions in hole-doped single-walled carbon nanotubes

We report the chemical vapor deposition growth of Nb-doped WS 2 monolayers and their characterization. Electron microscopy observations reveal that the Nb atom was substituted at the W site at a rate of approximately 0.5%. Unlike Mo doping, Nb-doped samples have photoluminescence (PL) peaks at 1.4-1.6 eV at room temperature. The peak energies are lower than the optical bandgap of 1.8 eV, and a saturation behavior of PL intensity is observed with the increase in excitation power. These results indicate that the observed PL peaks are assignable to the emission from impurity states generated by the substitution of Nb. © 2016 The Japan Society of Applied Physics T he optical properties of atomic-layer transition metal dichalcogenides (TMDCs) have recently attracted much attention owing to their wide-range bandgap energies from visible to infrared, 1-3) unique phenomena related to spin-valley physics, 4,5) and single-photon emission. [6][7][8][9] In particular, defect-derived excitonic states have recently received much attention for their applications in single-photon emitters. To date, several groups have reported that atomic-layer TMDCs show photoluminescence (PL) from optically active defects at low temperature (4 ∼ 90 K). 6-11) Such a two-dimensional (2D) single-quantum emission has practical advantages in efficient photon extraction and high integration capability. However, the details of such defect sites are still unclear, and PL can generally be observed only at low temperature. These issues may be resolved by the controlled fabrication of defect states, which is an important challenge in understanding and using TMDC atomic layers as quantum light sources.In general, defect states in low-dimensional materials are created through several mechanisms, including atomic vacancy formation, 12) impurity doping, [13][14][15][16] and chemical functionalization. 17) In this study, we have investigated impuritydoped WS 2 monolayers as a model system. Monolayer WS 2 is a semiconductor with a relatively wide direct bandgap and high air stability, and there have been many reports on its growth process and characterization. 10,[18][19][20][21][22] To implant impurities in WS 2 , we employed halide-assisted chemical vapor deposition (CVD), which was recently developed by Li et al. 21) This method can produce large-area monolayer WS 2 at relatively low temperatures (700°C) and under atmospheric pressure. Importantly, the use of halides can effectively transport precursors of transition metals, which usually have very low vapor pressure. As an impurity, Mo atoms are well studied and cause bandgap narrowing through the substitution of W sites in monolayer WS 2 . 14,15,23,24) However, there are very few studies on the doping of other transition metals for monolayer TMDCs. In the present study, Nb is selected because its atomic size is comparable to that of Mo and it is reported to generate acceptor states for some TMDCs. 16,25) Here, we report the synthesis and characterization of monolayer impurity-doped WS 2 using halide-ass...

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“…30,31) The three-level system consists of free excitons (X), localized excitons (L), and ground (g) states, as shown in the inset in Fig. 4(b).…”

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confidence: 99%

Growth and optical properties of Nb-doped WS₂ monolayers

Sasaki

Kobayashi

Liu³

et al. 2016

Appl. Phys. Express

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“…2(b)], which may be caused by a reduction of E 22 absorption cross section or changes in Auger recombination rates. In addi- (8,6), (9,7), and (14,3) nanotubes, respectively. Data are taken at zero gate voltage (black broken lines) and under an application of gate voltages (red solid lines).…”

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Gate-voltage induced trions in suspended carbon nanotubes

2016

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We observe trion emission from suspended carbon nanotubes where carriers are introduced electrostatically using field-effect transistor structures. The trion peak emerges below the E11 emission energy at gate voltages that coincide with the onset of bright exciton quenching. By investigating nanotubes with various chiralities, we verify that the energy separation between the bright exciton peak and the trion peak becomes smaller for larger diameter tubes. Trion binding energies that are significantly larger compared to surfactant-wrapped carbon nanotubes are obtained, and the difference is attributed to the reduced dielectric screening in suspended tubes.

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“…1(b)]. These investigations complement studies of gate-dependent Raman [13,14,27,28,41] and photoluminescence [13,37] spectroscopy of air-suspended nanotubes, gate-dependent Rayleigh scattering spectroscopy of individual nanotubes on substrates [52], and chemically-carrier-doped nanotubes [38,44,[47][48][49]51,53,57,61,62] showing spectral features attributed to formation of charged excitons (trions) [38]. We present all the Rayleigh spectra corrected for the ω 3 scattering efficiency factor to reflect directly the optical susceptibility.…”

Section: Introductionmentioning

confidence: 59%

“…Hence, the energy separation of the exciton and trion peaks is expected to be much larger than the energy range of the observed shift and broadening of the exciton peaks. Moreover, it has been reported that the optical absorption feature from the creation of trions is much smaller (less than 1/10) than that of the exciton absorption feature even under conditions of relatively heavy doping using chemical treatments [38], presumably because of the small oscillator strength of trions [57]. In the case of Rayleigh scattering spectra, the peak intensity from the creation of trions (if present) is expected to be still smaller because Rayleigh scattering cross section is proportional to the square of the optical susceptibility.…”

Section: B Exciton Energy Shiftmentioning

confidence: 99%

Tunable electronic correlation effects in nanotube-light interactions

et al. 2015

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Electronic many-body correlation effects in one-dimensional (1D) systems such as carbon nanotubes have been predicted to strongly modify the nature of photoexcited states. Here we directly probe this effect using broadband elastic light scattering from individual suspended carbon nanotubes under electrostatic gating conditions. We observe significant shifts in optical transition energies, as well as line broadening, as the carrier density is increased. The results demonstrate the role of screening of many-body electronic interactions on the different length scales, a feature inherent to quasi-1D systems. Our findings further demonstrate the possibility of electrical tuning of optical transitions and provide a basis for understanding of various optical phenomena in carbon nanotubes and other quasi-1D systems in the presence of charge carrier doping.

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Nonlinear photoluminescence properties of trions in hole-doped single-walled carbon nanotubes

Cited by 17 publications

References 34 publications

Growth and optical properties of Nb-doped WS₂ monolayers

Growth and optical properties of Nb-doped WS₂ monolayers

Gate-voltage induced trions in suspended carbon nanotubes

Tunable electronic correlation effects in nanotube-light interactions

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Nonlinear photoluminescence properties of trions in hole-doped single-walled carbon nanotubes

Cited by 17 publications

References 34 publications

Growth and optical properties of Nb-doped WS2 monolayers

Growth and optical properties of Nb-doped WS2 monolayers

Gate-voltage induced trions in suspended carbon nanotubes

Tunable electronic correlation effects in nanotube-light interactions

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Product

Resources

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Growth and optical properties of Nb-doped WS₂ monolayers

Growth and optical properties of Nb-doped WS₂ monolayers