excitons in atomically thin 2d semiconductors and their applications

Search in Google Scholar, [15] Shi H, Yan R, Bertolazzi S, et al. Science 2014;344:725–8. The excitons exhibit such a strong effect due to spatial confinement and reduced screening at the 2D limit, where even charged trions are observable at room temperature. Jun Xiao; Mervin Zhao; Yuan Wang; Xiang Zhang; Publication date 2017. Nat Rev Mater 2016;1:16055. The excitons of phosphorene also exhibit a large binding energy, once again due to the strong Coulomb interaction in two dimensions. The ability to reliably create monolayer semiconductors has been instrumental in unearthing the emerging physics and fabrication of 2D devices. Photoluminescence spectroscopy indicates an energy decrease of 45 meV per percent strain for monolayer and 120 meV per percent strain for bilayer MoS2 in the optical band gap (Figure 5C). Valleytronics in 2D materials. [48], where uniaxial tensile strain in the range of 0–2.2% modifies the phonon spectra and electronic band structure of monolayer and bilayer molybdenum MoS2 (Figure 5A,B). This SHG has been able to map out the grain boundaries in chemically grown MoS2 as well as distinguish the nonlinear differences of the chemically grown edges [35]. Nat Nanotechnol 2015;10:407–11. 6 (Issue 6), pp. Reprinted with permission from AAAS. In this paper, we review the progress on understanding the physical excitonic properties in 2D materials and the resulting applications from these quasiparticles. Atomic-layer graphene as a saturable absorber for ultrafast pulsed lasers. Dufferwiel et al. Here, by confining coherent excitons at the 2D quantum limit, we first observed molecular aggregation-enabled ‘supertransport’ of excitons in atomically thin two-dimensional (2D) organic semiconductors between coherent states, with a measured high effective exciton diffusion coefficient of ~346.9cm2/s at room temperature. Rycerz, A.; Tworzydło, J.; Beenakker, C. W. J. Chernikov, Alexey; Ruppert, Claudia; Hill, Heather M. Seyler, Kyle L.; Schaibley, John R.; Gong, Pu. Englund D, Fattal D, Waks E, et al. Such large binding energy results from the enhanced Coulomb interaction due to the strong confinement and heavy effective masses. Phys Rev B 2013;88:121301. Phys Rev Lett 2011;106:136806. Gunlycke D, White CT. Graphene valley filter using a line defect. TMDCs also have a hexagonal Brillouin zone like graphene with the band gaps occurring at the K points. BibTex; Full citation; Publisher: Walter de Gruyter GmbH. 6/26/2017. 114, Issue 9, Physical Review Letters, Vol. Excitons in atomically thin 2D semiconductors and their applications. Nat Commun 2012;3:887. Atomically thin p–n junctions with van der Waals heterointerfaces. The crystal structure of molybdenum disulfide (MoS 2) takes … Found inside – Page 219Monolayer MoS2 is a atomically thin semiconductor with direct bandgap in the visible spectral range, which holds great potential in many application ... In the weak coupling regime, where coupling strength g is much smaller compared with exciton linewidth Г, the Purcell effect dominates. Efficiency rolloff in OLEDs and inability to control morphology at key OPV interfaces both reduce EQE. 104, Issue 19, Nano Letters, Vol. 1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy. Nat Mater 2015;14:290–4. Amani M, Lien D-H, Kiriya D, et al. A monolayer TMDC (WS2) forms a heterojunction with (Ga, Mn)As and spin-polarized holes can be injected from (Ga, Mn)As to TMDC. This affects the overlap between the electron and holes, which also determines the optical transition strength. The broad spectra include emission from impurity-bound exciton (black arrow), charged exciton (red arrow for X− and grey arrow for X+), and neutral exciton (green arrow). Two-dimensional semiconducting systems have become increasingly important for a variety of applications including photo-detectors, high-power transistors and optoelectronics. 2.2 Excitons in atomically thin 2D materials. [47] demonstrated the continuous tuning of the electronic structure when applying a uniaxial tensile strain. Search in Google Scholar, [26] Ju L, Shi Z, Nair N, et al. (A) Diagram of K and −K valley energy levels shift under an out-of-plane magnetic field. Finally, the calculations show that the electronic band gap is approximately 2.7 eV, with an exciton binding energy of approximately 600–700 meV. Molybdenum disulfide belongs to a class of materials called 'transition metal dichalcogenides' (TMDCs). ACS Nano 2013;7:10741–6. Only exciting and detecting the armchair direction gives significant PL, while exciting and detecting the zigzag direction gives no PL. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. Miller DA. Phys Rev Lett 2015;114:037401. Nat Nano 2014;9:257–61. Within a monolayer, momentum-resolved spectroscopy showed that these exciton dipoles are only confined to the in-plane direction [14] with a lifetime in the 100-ps range before recombination [15]. Phys Rev Lett 2005;95:013904. Search in Google Scholar, [75] Lee HS, Kim MS, Jin Y, Han GH, Lee YH, Kim J. (d) Bias current-dependent EL intensity and spectra. In contrast to weak coupling, if g is comparable with or larger than Г, the excitons will experience strong coupling. In addition, there is a striking difference between the magnetic response of the neutral exciton and charged trions, due to the renormalization of excitonic spectrum arising from strong exchange interactions. Found insideThe aim of this book is to give readers a broad review of topical worldwide advancements in theoretical and experimental facts, instrumentation and practical applications erudite by luminescent materials and their prospects in dealing with ... 112, Issue 15, Applied Physics Letters, Vol. The book is divided into three parts that address: Semiconductor materials (i.e., carbon nanotubes, memristors, and spin organic devices) Silicon devices and technology (i.e. Scribd is the world's largest social reading and publishing site. The symposium will cover all relevant aspects of layered semiconductor materials: synthesis and chemical functionalization of these materials, their characterization with advanced techniques, and their applications in various fields. The large binding energies could potentially lead to room-temperature condensation in these very clean and versatile materials. Based on their estimation, complete ionization of the excitons can occur at a carrier density of several 1013 cm−2. Excitons in atomically thin 2D semiconductors and their applications. Lee C-H, Lee G-H, van der Zande AM, et al. Phys Rev Lett 2015;115:226801. (B) Anisotropic excitons of phosphorene. As it is an atomically thin semiconductor, it is possible to use the field effect to electrostatically dope carriers and thus tune the current in a transistor structure. Graphene mode-locked ultrafast laser. Search in Google Scholar, [29] Wu Z, Zhai F, Peeters FM, Xu HQ, Chang K. Valley-dependent Brewster angles and Goos-Hanchen effect in strained graphene. Recent work showed that stable quantum emitters can be positioned deterministically by placing a 2D material over protrusions in a substrate. Search in Google Scholar, [62] Withers F, Del Pozo-Zamudio O, Mishchenko A, et al. 71, Issue 11, Nanoscience and Technology: A Collection of Reviews from Nature Journals, p. 11-19, CLEO: Science and Innovations, Conference on Lasers and Electro-Optics, Advanced Optical Materials, Vol. Jun Xiao, Mervin Zhao, Yuan Wang, Xiang Zhang DOI: 10.1515/nanoph-2016-0160 Published: 22 June 2017. Cheiwchanchamnangij T, Lambrecht WRL. Found insideThis textbook presents the basic elements needed to understand and engage in research in semiconductor physics. Nat Rev Mater 2016;1:16055. Bonaccorso F, Sun Z, Hasan T, Ferrari A. Graphene photonics and optoelectronics. This high magnetic field is difficult to achieve with conventional magnets, yet it can be achieved using femtosecond light pulses [54], [56]. 3, Issue 12, Chemical Society Reviews, Vol. Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers. Search in Google Scholar, [86] Salehzadeh O, Djavid M, Tran NH, Shih I, Mi Z. Optically pumped two-dimensional MoS2 lasers operating at room-temperature. In addition, control of these excitons by optical, electrical, as well as mechanical means is examined. Emerging photoluminescence in monolayer MoS2. The coupling of 2D TMDCs with optical cavities was first reported by Gan et al. Orientation of luminescent excitons in layered nanomaterials. [52] and MacNeill et al. Our research focuses on excitons in 2D systems, including quantum wells in bulk semiconductors and atomically thin van der Waals materials. (A) Simplified picture of the electron bands near the K points of the Brillouin zone. The large binding energy in TMDCs is a result of the strong Coulomb interaction from the monolayer, large effective carrier masses, and weak dielectric screening. Search in Google Scholar, [53] MacNeill D, Heikes C, Mak KF, et al. The hexagonal nature of TMDCs and broken inversion symmetry of the monolayers makes them an ideal system to realize valley polarization. Phys Rev Lett 2014;113:076802. Finally, the resultant devices such as excitonic light emitting diodes, lasers, optical modulators, and coupling in an optical cavity are overviewed, demonstrating how excitons can shape future 2D optoelectronics. Phys Rev 1957;108:1384. Search in Google Scholar, [69] Bao Q, Zhang H, Wang B, et al. As the angular momentum of the system must be conserved, it is possible to easily summarize the selection rules as follows (schematically in Figure 2C) [33]: Upon absorption of incident light, the spin angular momentum of the photons, Δmћ, where m=±1 for σ± light, changes the angular momentum of the electrons in the valley (Δτћ, where τ=+1 (−1) for the −K (+K) valley, the angular momentum of the excitons (via the excitonic quantum number l), and the change in the angular momentum of the crystal lattice (3Nћ, resulting from the symmetry of the crystal). Found inside – Page 2099Likewise graphene, TMDCs have drawn an intense research progress due to inherent atomically thin 2D materials, transparent, flexible, and most importantly ... 13, Issue 4, p. 1416-1421, Nano Letters, Vol. Search in Google Scholar, [32] Cao T, Wang G, Han W, et al. Annu Rev Mater Res 2015;45:63–84. Mono-layer (1L) WSe 2 is a direct band-gap 2D semiconductor with a dark excitonic ground state 6,7. 113, Issue 10, Journal of Physics: Materials, Vol. In addition, control of these excitons by optical, electrical, as well as mechanical means is examined. In addition, low density of states near the Dirac point enables large Fermi level tunability via electrical gate. Nat Nanotechnol 2016;11:598–602. Search in Google Scholar, [22] Ugeda MM, Bradley AJ, Shi S-F, et al. © 2013. Nat Mater 2006;5:683–96. Only by creating materials that allow manipulation and control of the intimate assembly and communication between various nanoscale excitonic components can we hope to first understand and then engineer the system to allow these materials to reach, Optical selection rules fundamentally determine the optical transitions between energy states in a variety of physical systems, from hydrogen atoms to bulk crystals such as gallium arsenide. Hexagonally arranged transition metals (M) are sandwiched between two layers of chalcogen (X) atoms. Tightly bound trions in monolayer MoS2. Found inside – Page 30Electric field effect in atomically thin carbon films. Science. 2004;306(5696):666-669 ... Xu J, Zhang W, Feng P, semiconductors and their applications. These two-photon states do not appear in the linear one-photon absorption, therefore, “dark”, making it possible to use the two-photon absorption and subsequent bright-state luminescence (two-photon luminescence, TPL) to determine the excitonic structure of TMDCs [11]. 1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy. Akinwande D, Petrone N, Hone J. Two-dimensional flexible nanoelectronics. Exciton binding energy and nonhydrogenic rydberg series in monolayer WS2. Authors. Bao Q, Zhang H, Wang B, et al. [50] and Srivastava et al. The two-photon excitation energy is scanned, and the bright (“1s” exciton state) luminescence allows for observation of when the two-photons are on resonance with the dark excitonic states. Found inside – Page 26012.7 Summary The TMDs are 2D semiconductor materials showing unique electrical, ... of the transition from indirect to direct bandgap in atomically thin ... Nat Nano 2012;7: 490–3. Nat Commun 2013;4:1474. Hendry E, Hale PJ, Moger J, Savchenko A, Mikhailov S. Coherent nonlinear optical response of graphene. (D) Valley polarization degree for excitons as a function of field strength. Found inside – Page 90... Seminar in the Physics Department at the University of Kansas, April 15, ... Li “ Coherent Electronic Coupling in Atomically Thin Semiconductors”, ... In addition to using a magnetic field to lift the valley degeneracy, light can generate a pseudo-magnetic field. Nat Nano 2013;8:271–6. The monolayer nature of TMDCs makes it easy to tune the Fermi level and varies the carrier concentration using a field-effect transistor (FET) device [19]. (D) The excitonic energies are given on the left. The laser excitation is at 1.95 eV with σ+ polarization. Namely, by engineering external photonic density of states, the exciton decay rate changes accordingly by the Purcell factor [71], [72]. Search in Google Scholar, [33] Xiao J, Ye Z, Wang Y, Zhu H, Wang Y, Zhang X. Nonlinear optical selection rule based on valley-exciton locking in monolayer WS2. Also, they found the extra charge binding energies for X+ and X− to be nearly the same, indicating the similar effective mass for electrons and holes, which is consistent with theoretical calculations. Transition metal dichalcogenide (TMD or TMDC) monolayers are atomically thin semiconductors of the type MX 2, with M a transition metal atom (Mo, W, etc.) (C) Scanning photocurrent image at 100 K shows dominant photocurrent generation mainly in the junction. Phys Rev Lett 2015;115:126802. Srivastava, Ajit; Sidler, Meinrad; Allain, Adrien V. Schaibley, John R.; Yu, Hongyi; Clark, Genevieve. "Excitons in atomically thin 2D semiconductors and their applications". Selective amplification of the primary exciton in a MoS2 monolayer. Experimentally, these selection rules have been verified showing that SHG produces light of opposite circular polarization to the incident photons while the TPL process will preserve the circular polarization [33], [36]. 103, Issue 18, Physical Review Letters, Vol. Orange (K) and green areas (−K) show the electron-hole overlap accouting for photon emission of the given polarizations. Atomically thin p–n junctions with van der Waals heterointerfaces. Found inside – Page 50Synthesis, Assembly, and Applications Geon Dae Moon ... Yao W, Xu X (2016) Valley-polarized exciton dynamics in a 2D semiconductor heterostructure. Adapted with permission from Macmillan Publishers Ltd., Nature Communications [10], © 2013. Search in Google Scholar, [67] Sun Z, Hasan T, Torrisi F, et al. Full text. Geim AK, Novoselov KS. The parity selection from TPL indicates that there are selection rules that govern valley excitations, which include nonlinear excitations. [74] placed monolayer WSe2 onto a photonic crystal (PhC) with a cavity and effectively coupled cavity-mode emission resulting in ~60 times enhanced PL and a strong pattern of the emission angle in the sub-wavelength scale (Figure 10A,B). Nano Lett 2015;15:5302–6. DOI identifier: 10.1515/nanoph-2016-0160. Nano Lett 2013;13:1416–21. Monolayer MoS2 was transferred onto the cavity after exfoliation on a polymer substrate. Broadband graphene polarizer. [53] used circularly polarized PL in MoSe2 under magnetic fields up to 10 T. Neutral and charged excitons shift linearly with field strength at a rate of ∓0.12–22 meV per Tesla for emission arising from the ±K valleys, indicating the lifting of the valley degeneracy. Appl Phys Lett 2013;103:181119. Search in Google Scholar, [17] Esser A, Runge E, Zimmermann R, Langbein W. Photoluminescence and radiative lifetime of trions in GaAs quantum wells. Nat Phy 2015;11:141–7. Annu Rev Mater Res 2015;45:63–84. In contrast, inversion symmetric crystals like graphene, Ω and m must take on the same values under inversion, thus K and −K become indistinguishable. Sci Rep 2016;6:33134. Experimental demonstration of continuous electronic structure tuning via strain in atomically thin MoS2. Search in Google Scholar, [31] Xu X, Yao W, Xiao D, Heinz TF. However, graphene has had difficulty in generating a valley “current,” requiring configurations such as bilayer domain walls [26], specific crystalline edges [27], [28], or strain [29]. In addition, monolayer TMDCs with inversion symmetry breaking can exhibit strong second-order nonlinearity. Feldmann J, Peter G, Göbel E, et al. Adv Funct Mater 2009;19:3077–83. The left (right) pair corresponds to the K (−K) valley. In contrast to other 2D materials, freestanding atomically thin Ga are unstable: their crystal structures will spontaneously collapse if there is no specific substrate to stabilize them. Kang K, Xie S, Huang L, et al. Materials for flexible, stretchable electronics: graphene and 2D materials. Search in Google Scholar, [30] Xiao D, Yao W, Niu Q. Valley-contrasting physics in graphene: magnetic moment and topological transport. They are part of the large family of so-called 2D materials, named so to emphasize their extraordinary thinness. (E) Optical absorption of two layer WS2 with and without an intense laser pump after substraction of a linear background. [42] investigated the electrostatic gate effect on PL of positively charged (X+), neutral (X0), and negatively charged (X−) excitons in monolayer MoSe2. 2D Materials™ is a multidisciplinary, electronic-only journal devoted to publishing fundamental and applied research of the highest quality and impact covering all aspects of graphene and related two-dimensional materials. Phys Rev Lett 2015;114:097403. Nano Lett 2013;13:2931–6. This effect is based on the coherent interaction between an exciton and a photon, understood via Floquet theory [54]. Broadband graphene polarizer. Thus, understanding and manipulating the excitons are crucial to unlocking the potential of 2D materials for future photonic and optoelectronic devices. Spin and pseudospins in layered transition metal dichalcogenides. Super-transport of Excitons in Atomically Thin Organic Semiconductors at the 2D Quantum Limit Ankur Sharma,1 Linglong Zhang,1 Jonathan O. Tollerud2, Miheng Dong,1 Yi Zhu,1 Robert Halbich,1 Tobias Vogl,3 Kun Liang,1,4, Hieu T. Nguyen,1 Fan Wang,5 Shilpa Sanwlani2, Stuart K. Earl2, Daniel Macdonald,1 Ping Koy Lam,3 Jeff A. Davis2 and Yuerui Lu1* 1Research School of Engineering, … Nat Mater 2015;14:290–4. (A–D) Adapted with permission from Macmillan Publishers Ltd., Nature Photonics [80], © 2016. Control of two-dimensional excitonic light emission via photonic crystal. Nat Nanotechnol 2016;11:598–602. Nat Mater 2015;14:301–6. Graphene mode-locked ultrafast laser. The electric field itself was found to not appreciably modulate the dielectric constant in single layers, thus electrical control is more of an access to the monolayer’s carrier concentrations [44]. Also, the spontaneous polarization fields in nitride heterostructures allow IXs to form in atomically thin GaN quantum wells … Search in Google Scholar, [52] Li Y, Ludwig J, Low T, et al. Found inside – Page 178In these molybdenum disulfide thin-film transistors, when we increase the gate voltage to ... The vertical hetero-structured surface of the atomically thin ... Mapping out the full spectra clearly shows two new peaks in the two-photon excitation from 2.1 to 2.6 eV, corresponding to two higher energy dark states, the “2p” and “3p” states (Figure 1D). Atomically thin MoS2: a new direct-gap semiconductor. Transition metal dichalcogenides (TMDCs) exhibit remarkable electronic properties when thinned down to the monolayer limit. Coherent coupling of WS2 monolayers with metallic photonic nanostructures at room temperature. E3d2000) optical ring resonator. As plotted in Figure 9D, the TMDC emission helicity hysteresis as a function of magnetic field is consistent and dependent upon the magnetization hysteresis of (Ga, Mn)As, confirming that valley carriers were generated by spin injection from (Ga, Mn)As. Search in Google Scholar, [42] Ross J S, Wu S, Yu H, et al. The exciton’s large oscillator strength and enhanced light-matter interaction allow for efficient recombination and emission of light [2]. Interestingly, under forward and reverse biases, ±K valleys are affected differently. Thus, a naturalistic application for direct band gap 2D semiconductors is in the development of bright, flexible, and ultra-thin LEDs. Valley-selective circular dichroism of monolayer molybdenum disulphide. Monolayer TMDCs preserve time reversal symmetry, with energetically degenerate excitons in the ±K valleys. Phys Rev B 2013;88:121301. Exciton-dominant electroluminescence from a diode of monolayer MoS2. Clearly, there is a discrepancy in the binding energy of the excitons, perhaps arising from the crystal sources, but this can be approximated at 500 meV. Control of valley polarization in monolayer MoS2 by optical helicity. Unlike graphene, TMDCs and black phosphorus exhibit direct bandgaps for resonant light absorption, offering properties complementary to graphene. The green curve is the differential reflectance of the linear absorption, showing that the 2p state has no corresponding linear absorption. Found insideThis book presents the first established experimental results of an emergent field: 2-dimensional materials as platforms for quantum technologies, specifically through the optics of quantum-confined excitons. Phys Rev Lett 2011;106:176802. Highly reflective DBRs form a cavity to trap photons, and MoS2 was designed to be placed at the antinode of the mode to have maximum coupling with the photons. Elliott R. Intensity of optical absorption by excitons. Graphene was the first ‘modern’ 2D material to be isolated in 2004 .Since then, there have been literally hundreds of other examples , with an extensive range of properties. In graphene, the crystal momentum space’s Brillouin zone is hexagonal. The trion binding energy is defined as the energy difference between the trion and the neutral exciton. Sun Z, Hasan T, Torrisi F, et al. El in a monolayer semiconductor two palladium back-gates ( Vg1 and Vg2 can. American chemical Society Reviews, Vol Center ; Lawrence Berkeley National Lab: magnetic moment and topological transport Flatten,. From these quasiparticles nonlinear susceptibility for modulation applications such as saturable absorbers polarized. Coupling at room temperature ] Flatten LC, He Z, Hasan T, Sun Z, et al from! Behavior of an exciton and a 0D quantum dot Berkelbach TC, Hill HM, Rigosi AF, Heinz.! Semiconductors and their applications of radiative exciton lifetimes in quantum wells 2017 ; Nanophotonics (! Berkeley National Lab magnitude and sign of ∆E are dependent on the recombination produces light color. With a femtosecond pulsed laser at 10 K, Poole C, Mak,! To observe and control of the monolayers makes them an ideal system to realize polarization... Demand for compact, efficient, fast, and black phosphorous may meet the demand! Emerging demand for compact, efficient, fast, and broadband optical modulators photo-excitation semiconductors. Wse2 flakes it shows significant band renormalization and excitonic effects in a microcavity ( 7A... Wang ; Xiang Zhang 55 ] Chernikov a, van der Zande AM, et al a for. Junctions of an electric-double-layer transistor based on the material Yu Y, Mak,... Engineering in van der Waals materials, Vol narrow-band high-lying excitons wih negative-mass electron - online. Two distributed Bragg reflector mirrors, Liu B, Naylor CH, et al R. Yu..., then Sun L, Kong J, et al [ 36 ] S. 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