Giant Negative Terahertz Photoconductivity in Controllably Doped Carbon Nanotube Networks

Burdanova, Maria G.; Tsapenko, Alexey P.; Satco, Daria A.; Kashtiban, Reza J.; Mosley, Connor Devyn William; Monti, Maurizio; Staniforth, Michael; Sloan, Jeremy; Gladush, Yuriy G.; Nasibulin, Albert G.; Lloyd‐Hughes, James

doi:10.1021/acsphotonics.9b00138

Cited by 41 publications

(53 citation statements)

References 80 publications

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“…We therefore conclude that the change of photoconductivity observed upon push–pulse arrival is neither related to a change in the free-carrier density (previously proposed to result from hot-carrier trapping 39 ), nor to changes in the mobility of charge carriers. 43 These mechanisms would cause a significant change in the DC (0 THz) conductivity that is absent in the data shown in Figure 5 . Instead, the interaction of hot carriers with the THz pulse results in stimulated emission of THz photons, increasing the apparent transmission of the probe and leading to a reduction of the apparent THz conductivity, as calculated directly from the transmission intensity of the probe.…”

Section: Resultsmentioning

confidence: 96%

“…We note that previous discussions of negative photoconductivity have focused exclusively on low-dimensional materials such as graphene 44 − 47 and doped nanowires. 43 Therefore, we hope that our discovery of negative photoconductivity in a 3D bulk semiconductor such as tin-iodide perovskite will trigger further discussion about origins of photoinduced conductivity reductions in semiconductors.…”

Section: Resultsmentioning

confidence: 99%

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Revealing Ultrafast Charge-Carrier Thermalization in Tin-Iodide Perovskites through Novel Pump–Push–Probe Terahertz Spectroscopy

et al. 2021

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Tin-iodide perovskites are an important group of semiconductors for photovoltaic applications, promising higher intrinsic charge-carrier mobilities and lower toxicity than their lead-based counterparts. Controllable tin vacancy formation and the ensuing hole doping provide interesting opportunities to investigate dynamic intraband transitions of charge carriers in these materials. Here, we present for the first time an experimental implementation of a novel Optical-Pump–IR-Push–THz-Probe spectroscopic technique and demonstrate its suitability to investigate the intraband relaxation dynamics of charge carriers brought into nonequilibrium by an infrared “push” pulse. We observe a push-induced decrease of terahertz conductivity for both chemically- and photodoped FA 0.83 Cs 0.17 SnI 3 thin films and show that these effects derive from stimulated THz emission. We use this technique to reveal that newly photogenerated charge carriers relax within the bands of FA 0.83 Cs 0.17 SnI 3 on a subpicosecond time scale when a large, already fully thermalized (cold) population of charge-carriers is present. Such rapid dissipation of the initial charge-carrier energy suggests that the propensity of tin halide perovskites toward unintentional self-doping resulting from tin vacancy formation makes these materials less suited to implementation in hot-carrier solar cells than their lead-based counterparts.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Revealing Ultrafast Charge-Carrier Thermalization in Tin-Iodide Perovskites through Novel Pump–Push–Probe Terahertz Spectroscopy

et al. 2021

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“…The dielectric constant of L = 10 was used in the calculations to represent polarisation effect of the crystal lattice and the photoconductivity and dark conductivity due to free charge-carriers in the film were assumed to be real (DC Drude conductivity) photoconductivities, lower than 10 −1 cm −1 in the case of 400-nm-thick films. However, neither of the equations discussed above provides enough accuracy for calculating the photoconductivity of doped semiconductors, as has been previously pointed out by Burdanova et al [34]. These approximations assume a lack of conductivity of the unexcited sample, which is invalid in doped semiconductors.…”

Section: Photoconductivity: Common Approachmentioning

confidence: 96%

Terahertz Conductivity Analysis for Highly Doped Thin-Film Semiconductors

Ulatowski

Herz

Johnston

2020

J Infrared Milli Terahz Waves

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The analysis of terahertz transmission through semiconducting thin films has proven to be an excellent tool for investigating optoelectronic properties of novel materials. Terahertz time-domain spectroscopy (THz-TDS) can provide information about phonon modes of the crystal, as well as the electrical conductivity of the sample. When paired with photoexcitation, optical-pump-THz-probe (OPTP) technique can be used to gain an insight into the transient photoconductivity of the semiconductor, revealing the dynamics and the mobility of photoexcited charge carriers. As the relation between the conductivity of the material and the THz transmission function is generally complicated, simple analytical expressions have been developed to enable straightforward calculations of frequency-dependent conductivity from THz-TDS data in the regime of optically thin samples. Here, we assess the accuracy of these approximated analytical formulas in thin films of highly doped semiconductors, finding significant deviations of the calculated photoconductivity from its actual value in materials with background conductivity comparable to 102Ω− 1cm− 1. We propose an alternative analytical expression, which greatly improves the accuracy of the estimated value of the real photoconductivity, while remaining simple to implement experimentally. Our approximation remains valid in thin films with high dark conductivity of up to 104Ω− 1cm− 1 and provides a very high precision for calculating photoconductivity up to 104Ω− 1cm− 1, and therefore is highly relevant for studies of photoexcited charge-carrier dynamics in electrically doped semiconductors. Using the example of heavily doped thin films of tin-iodide perovskites, we show a simple experimental method of implementing our correction and find that the commonly used expression for photoconductivity could result in an underestimate of charge-carrier mobility by over 50%.

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“…[213,229,230] Jensen et al [229] performed a comparative study of the ultrafast electronic transport in graphene nanoribbons and in semiconducting carbon nanotubes: both types of spectra were fit by a Drude-Smith model and the scattering time in CNTs was found to be significantly longer than in carbon nanoribbons. [213,229,230] Jensen et al [229] performed a comparative study of the ultrafast electronic transport in graphene nanoribbons and in semiconducting carbon nanotubes: both types of spectra were fit by a Drude-Smith model and the scattering time in CNTs was found to be significantly longer than in carbon nanoribbons.…”

Section: Thz Response Of Carbon Nanotubesmentioning

confidence: 99%

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

Kužel

Němec

2019

Advanced Optical Materials

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Transport of charges is a fundamental process in many high-tech applications including photovoltaic or optoelectronic devices, but also in more ordinary components such as unsophisticated wires and other circuitry. The development of nanotechnologies resulted in the fabrication of highly complex materials consisting of a large variety of nanosized elements, which inevitably involve a multitude of charge transport processes occurring on various time-and length-scales. Figure 1 summarizes the most common nanoelements with high application potential.For example, the electrodes employed in Grätzel solar cells [1] are composed of percolated networks of a huge number of metal oxide nanoparticles (top-left panel in Figure 1). Colloidal nanocrystals form the basis for thin film electronics and flexible electronic devices. [2] The synthetic approaches control their composition, size and electronic structure (energy levels, density of states within the bands and in the bandgap) and the charge-carrier transport. [2,3] Nanowires and nanotubes made of conventional semiconductors are quasi 1D systems combining Terahertz spectroscopy has been used for almost two decades for investigations of nanomaterials, including nanocrystals, nanoparticles, nanowires, nanotubes or 2D crystals. Its great importance stems from the fact that it is a noncontact method and, owing to its high frequency and broadband character, it is capable of characterizing charge transport properties within individual nano-objects but also among them. In addition, probing of photoinitiated ultrafast charge dynamics is possible thanks to the sub-picosecond time resolution. Despite this unprecedented potential, the interpretation of the measured terahertz conductivity spectra in many materials is still intensively debated. Herein is presented a review of the experiments performed on nanostructures of conventional semiconductors and on carbon nanomaterials (graphene and carbon nanotubes) during the past decade. The state of the art of the theoretical formalism is provided and discussed, including the intrinsic response, as well as the role of inherent heterogeneity and of the experimental conditions.

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Giant Negative Terahertz Photoconductivity in Controllably Doped Carbon Nanotube Networks

Cited by 41 publications

References 80 publications

Revealing Ultrafast Charge-Carrier Thermalization in Tin-Iodide Perovskites through Novel Pump–Push–Probe Terahertz Spectroscopy

Revealing Ultrafast Charge-Carrier Thermalization in Tin-Iodide Perovskites through Novel Pump–Push–Probe Terahertz Spectroscopy

Terahertz Conductivity Analysis for Highly Doped Thin-Film Semiconductors

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

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