Experimental Verification of Carrier Multiplication in Graphene

Plötzing, Tobias; Winzer, Torben; Malić, Ermin; Neumaier, Daniel; Knorr, Andreas; Kurz, H.

doi:10.1021/nl502114w

Cited by 102 publications

(124 citation statements)

References 26 publications

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“…So a lower cooling rate (longer lifetime of hot electrons) leads to a larger photocurrent. The electron heating and cooling dynamics in bulk graphene have been studied using pump-probe measurements, such as optical pumpprobe [22,31,33,34], femtosecond time-resolved angleresolved photo-electron spectroscopy (ARPES) [30,32], and time-resolved optical pump-terahertz (THz) probe spectroscopy [26,[35][36][37][38][39][40][41]. The photoexcited carrier dynamics have also been studied in graphene-based devices through time-resolved photocurrent scanning microscopy [7,8,17,29].…”

Section: Time-resolved Photocurrentmentioning

confidence: 99%

Hot-carrier photocurrent effects at graphene–metal interfaces

Tielrooij¹,

Massicotte²,

Piątkowski³

et al. 2015

J. Phys.: Condens. Matter

102

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Photoexcitation of graphene leads to an interesting sequence of phenomena, some of which can be exploited in optoelectronic devices based on graphene. In particular, the efficient and ultrafast generation of an electron distribution with an elevated electron temperature and the concomitant generation of a photo-thermoelectric voltage at symmetry-breaking interfaces is of interest for photosensing and light harvesting. Here, we experimentally study the generated photocurrent at the graphene-metal interface, focusing on the time-resolved photocurrent, the effects of photon energy, Fermi energy and light polarization. We show that a single framework based on photo-thermoelectric photocurrent generation explains all experimental results.

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Section: Time-resolved Photocurrentmentioning

confidence: 99%

Hot-carrier photocurrent effects at graphene–metal interfaces

Tielrooij¹,

Massicotte²,

Piątkowski³

et al. 2015

J. Phys.: Condens. Matter

102

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“…A signi cant carrier multiplication has been theoretically predicted [30,130,134] and experimentally con rmed in graphene [32,101,128,133,135]. So far, the theoretical studies have been constrained to the case of undoped graphene.…”

Section: Carrier Multiplication In Doped Graphenementioning

confidence: 99%

“…The e cient carrier-carrier and carrier-phonon scattering processes quickly relax the hot carriers into an isotropic thermal distribution, which is then followed by carrier cooling due to carrier-phonon processes [17,22,23]. A variety of dynamical phenomena, such as the appearance of a signi cant carrier multiplication and transient optical gain, have been theoretically predicted [30 33] and experimentally con rmed [32,34,35]. A consistent treatment of the relaxation dynamics containing all important scattering contributions can be realized within the density matrix approach [17,36,37].…”

Section: Motivationmentioning

confidence: 99%

“…Immediately after photoexcitation, the phase space for impact ionization processes is large, while Auger recombination processes are inhibited, which leads to a signi cant carrier multiplication in the conduction band up to a moderate excitation regime [30,35]. Again, the strong intraband and interband carrier-carrier scattering processes establish a single uniform hot-carrier Fermi-Dirac distribution on an ultrafast timescale followed by hot-carrier cooling via optical and acoustic phonon emission.…”

Section: Terahertz Carrier Dynamicsmentioning

confidence: 99%

“…Here, one has to distinguish between the carrier generating impact excitation (IE) and its inverse process, the Auger recombination (AR). In distinct excitation regimes, the IE has a higher probability than AR leading to a theoretically predicted and experimentally con rmed carrier multiplication (CM) [30,128,133,135]. CM is generally de ned as the ratio between the number of overall generated electron-hole pairs and the optically excited charge carriers:…”

Section: Carrier Multiplication In Doped Graphenementioning

confidence: 99%

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Relaxation Dynamics in Graphene

Malić

Knorr

2013

Graphene and Carbon Nanotubes

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In this thesis, the relaxation dynamics of nonequilibrium carriers in graphene is investigated. Based on the density matrix approach, the interaction of carriers with light, phonons and electrons is theoretically modelled. The resulting time-, momentum-, and angle-resolved simulation of the carrier dynamics enables the interpretation of recent experimental observations. Typically, the carrier relaxation has been accessed via high-resolution pump-probe experiments. Common to all studies is a bi-exponential decay of the pump-induced differential transmission (DT) spectrum. The fast decay component in the range of few tens of femtoseconds is assigned to an ultrafast Coulomb-dominated carrier redistribution towards a hot Fermi-Dirac distribution, whereas the slower decay component in the range of a picosecond reflects the equilibration between the electron and the phonon system. However, many studies report a zero-crossing after the initial decay in the transient DT spectrum, where the second decay component characterizes the recovering of the DT signal. In very good agreement with recent pump-probe experiment performed by the group of Prof. Manfred Helm (Helmholtz-Zentrum Dresden-Rossendorf), a microscopic explanation for the occurrence of transient negative differential transmission in graphene is found, where a detailed interplay of intraand interband absorption processes on the transient DT in graphene is investigated. In particular, phonon-assisted intraband processes are shown to lead to an enhanced absorption giving rise to the experimentally observed zero-crossing from positive to negative DT signals.In collaboration with the group of Prof. Theodore B. Norris (Michigan University, USA), theoretical studies combined with ultrafast time-resolved THz spectroscopy were performed to systematically investigate the hot-carrier dynamics in an array of graphene samples. The theory calculates explicitly the time-dependent response of the system to a THz probe pulse. The calculations reveal that the observed dynamics can be accounted for qualitatively without including any fitting parameters, phenomenological models or extrinsic effects. Specifically, the hot-carrier dynamics are governed by the coupling of extraordinarily efficient carrier-carrier and carrier-phonon interactions. Furthermore, the theory demonstrates that the simple Drude model is insufficient to fully account for the THz interactions.Beside pump-probe studies, the thesis presents the absorption spectra of mono-and bilayer graphene including the impact of the fully momentum-dependent optical and Coulomb matrix elements. In agreement with recent experiments, the absorbance of graphene is characterized by a frequency-independent value in the near-infrared spectral region and a pronounced peak in the ultraviolet region resulting from interband transition. In contrast to the linear band structure of graphene, the energy dispersion of bilayer graphene exhibits four parabolic bands resulting in interesting optical features: The absorbance exhibits in...

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Progress, Challenges, and Opportunities for 2D Material Based Photodetectors

Long

Wang

Fang

et al. 2018

Adv Funct Materials

1,073

872

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2D material based photodetectors have attracted many research projects due to their unique structures and excellent electronic and optoelectronic properties. These 2D materials, including semimetallic graphene, semiconducting black phosphorus, transition metal dichalcogenides, insulating hexagonal boron nitride, and their various heterostructures, show a wide distribution in bandgap values. To date, hundreds of photodetectors based on 2D materials have been reported. Here, a review of photodetectors based on 2D materials covering the detection spectrum from ultraviolet to infrared is presented. First, a brief insight into the detection mechanisms of 2D material photodetectors as well as introducing the figure-of-merits which are key factors for a reasonable comparison between different photodetectors is provided. Then, the recent progress on 2D material based photodetectors is reviewed. Particularly, the excellent performances such as broadband spectrum detection, ultrahigh photoresponsivity and sensitivity, fast response speed and high bandwidth, polarization-sensitive detection are pointed out on the basis of the state-of-the-art 2D photodetectors. Initial applications based on 2D material photodetectors are mentioned. Finally, an outlook is delivered, the challenges and future directions are discussed, and general advice for designing and realizing novel high-performance photodetectors is given to provide a guideline for the future development of this fast-developing field.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201803807. atomic layer, while these atomically thin layers are bonded together by weak van der Waals interactions along the third dimension perpendicular to the 2D plane. The weak interlayer interaction makes it possible to exfoliate bulk crystals into isolated thin 2D flakes and even a single atomically thin layer.A photodetector is a device that can convert a light signal into an electrical signal. High performance photodetectors play important roles in many fields of our daily life, including electro-optical displays, imaging, environment monitoring, optical communication, military, security checking and so forth. 2D materials, as one of most competitive materials for designing photodetectors, have been demonstrated with remarkable characteristics, including broad detection waveband covering the wavelengths from UV to terahertz frequencies (THz, 10 12 Hz), ultrahigh photoresponsivity, polarization sensitive photodetection, high-speed photoresponse, high spatially resolved imaging, etc. Thanks to the recently developed dry transfer technique, [1] various heterostructures based on 2D materials have been designed and fabricated with desirable band alignments. Photodetectors based on these heterostructures have exhibited enhanced performances like high photovoltaic external quantum efficiency up to 30% for graphene-WS 2 -graphene, [2] ultrahigh photoresponsivity up to ≈10 10 A W −1 for graphene-MoS 2 , [3] ultrahigh photogain ...

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Experimental Verification of Carrier Multiplication in Graphene

Cited by 102 publications

References 26 publications

Hot-carrier photocurrent effects at graphene–metal interfaces

Hot-carrier photocurrent effects at graphene–metal interfaces

Relaxation Dynamics in Graphene

Progress, Challenges, and Opportunities for 2D Material Based Photodetectors

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