Role of Photoinduced Exciton in the Transient Terahertz Conductivity of Few-Layer WS<sub>2</sub> Laminate

Xing, Xiao; Zhao, Linjie; Zhang, Zeyu; Liu, Xiankuan; Zhang, Kailin; Yu, Yang; Lin, Xian; Chen, Hua Ying; Chen, Jin Quan; Jin, Zuanming; Xu, Jianhua; Ma, Guohong

doi:10.1021/acs.jpcc.7b05345

Cited by 45 publications

(45 citation statements)

References 54 publications

(110 reference statements)

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“…Furthermore, for the indirect semiconductor, momentum conservation requires assistance from phonons . Meanwhile, the charge carriers and excitons could coexist in TMD materials through photoexcitation . From these statements, based on the above relaxation pathway model by taking into account the dissociation of exciton, the dynamics of charge carriers and excitons could be described by the following rate equations:

\frac{d C (t)}{d t} = G_{1} (t) - C (t) / τ_{normal1} - C (t) / τ_{normal2} + W (t) / τ_{normal3}

\frac{d W (t)}{d t} = G_{2} (t) - W (t) / τ_{normal3} - W (t) / τ_{normal4}

where C ( t ) and W ( t ) represent the time‐dependent charge and exciton populations, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…These defects are believed to serve as either effective recombination centers or effective carrier traps . Defect‐trapped processes could exhibit pump fluence dependence even under medium pump intensity for the decay time constant . Hence, the decay component τ 2 (≈200–280 ps) could be attributed to charge recombination via defect‐assistance (Figure c).…”

Section: Resultsmentioning

confidence: 99%

“…Optical‐pump THz‐probe (OPTP) spectroscopy is a suitable tool for the measurement of complex photoconduction after optical excitation due to either free carriers or bounded excitons in a nondestructive way. Previously, the free carriers and the bounded carriers were studied in materials by pump delay time scanning at the peak and zero‐crossing of terahertz (THz) waveform, respectively. But the ratio of the free carriers to excitons has not been studied yet.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy

Zhu

Zhao

et al. 2018

Advanced Optical Materials

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are new types of semiconductors in which adjacent layers are held by van der Waals force. [1] TMDs have many rich physical properties such as extremely weak phonon-assisted photoluminescence (PL) in bulk structures, relatively strong PL yield in monolayer structures, [2][3][4][5] strong valley-dependent absorption in visible range, [6][7][8] and strong nonlinear optical response. [9][10][11][12] By taking advantage of these properties, significant progresses have been made in the development of electronic and optoelectronic technologies by these materials, [13,14] such as photodetectors, [15] field-effect transistors, [16][17][18] solar cells, [19,20] light-emitting diodes, [21,22] valleytronics, [8,23] integrated circuits, [24] and so on.The exciton binding energy in the monolayer TMDs has been observed in the range of 0.1-1.1 eV, [25][26][27][28] which is larger than that in traditional bulk semiconductors and traditional quantum well. [29,30] This rich excitonic state makes it possible to observe the complex exciton dynamics at room temperature, [31] such as charged and neutral phase of carriers, [32] trions, [33] and biexciton. [34] Meanwhile, bounded exciton could not only dominate the optical response but also play an important role in the optoelectronic processes, such as photocurrent generation and photoconduction in TMD semiconductors. [33,35,36] As a typical TMD material, the bulk WSe 2 has an indirect bandgap of 1.2 eV, and it would transform to the ≈1.65 eV direct bandgap as decreasing to monolayer. [37,38] WSe 2 has been widely used in optoelectronic devices due to its high absorption coefficients in the visible range. Field-effect transistors based on single crystal WSe 2 have been achieved and a carrier mobility comparable to silicon at room temperature was demonstrated. [39] Besides, WSe 2 can also play an important role in the development of van der Waals heterostructures, [40][41][42] in which long-lived interlayer excitons have been observed.Recently, ultrafast time-resolved photoexcited carrier dynamics has been studied in layered TMDs by the most widely used tools, such as optical-pump optical-probe spectroscopy, [43] PL spectroscopy, [38] photocurrent spectroscopy, [36] and electroluminescence. [35,44] The prevalentThe dynamics of photoexcited species is quite important for the development of next-generation ultrafast optoelectronic devices based on transition metal dichalcogenides (TMDs). Herein, time-resolved optical pump terahertz (THz) probe spectroscopy, which is sensitive to both bounded excitons and free electrons/holes, is employed to study the dynamics of photo-induced carriers in the typical layered TMDs crystal tungsten diselenide (WSe 2 ). Initial photoexcitation could generate both free carriers and excitons. The free carriers decay followed by phonon-assistance (≈30 ps) and defect-assistance (≈200-280 ps). The excitons decay followed by the phonon-assisted recombination (≈100 ps) and the defect-induced exciton separation (≈40-200 ps). With the increasing of pump fluence, more f...

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\frac{d C (t)}{d t} = G_{1} (t) - C (t) / τ_{normal1} - C (t) / τ_{normal2} + W (t) / τ_{normal3}

\frac{d W (t)}{d t} = G_{2} (t) - W (t) / τ_{normal3} - W (t) / τ_{normal4}

where C ( t ) and W ( t ) represent the time‐dependent charge and exciton populations, respectively.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy

Zhu

Zhao

et al. 2018

Advanced Optical Materials

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show abstract

“…Following the previous studies on transition metal dichalcogenides (47,51), to unveil the exciton dynamics in the 2D perovskite, we fitted the measured imaginary part of photoconductivity ( Fig. 2B) using biexponential decay function and the fitted parameters are shown in Table 2.…”

Section: Introductionmentioning

confidence: 99%

Excitons in 2D perovskites for ultrafast terahertz photonic devices

et al. 2020

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In recent years, two-dimensional (2D) Ruddlesden-Popper perovskites have emerged as promising candidates for environmentally stable solar cells, highly efficient light-emitting diodes, and resistive memory devices. The remarkable existence of self-assembled quantum well (QW) structures in solution-processed 2D perovskites offers a diverse range of optoelectronic properties, which remain largely unexplored. Here, we experimentally observe ultrafast relaxation of free carriers in 20 ps due to the quantum confinement of free carriers in a self-assembled QW structures that form excitons. Furthermore, hybridizing the 2D perovskites with metamaterials on a rigid and a flexible substrate enables modulation of terahertz fields at 50-GHz modulating speed, which is the fastest for a solution-processed semiconductor-based photonic device. Hence, an exciton-based ultrafast response of 2D perovskites opens up large avenues for a wide range of scalable dynamic photonic devices with potential applications in flexible photonics, ultrafast wavefront control, and short-range wireless terahertz communications.

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“…[96,121,122] Although these studies (1). Most popular TMDCs such as MoS 2 , WS 2, and WSe 2 exhibit semiconducting behavior.…”

Section: Terahertz Saturable Absorbersmentioning

confidence: 99%

2D Materials for Terahertz Modulation

Gopalan

Sensale‐Rodriguez

2019

Advanced Optical Materials

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power consumption and minimizing cross-talk (maintain signal fidelity). As a result, terabit data communication can be made feasible with the help of broadband all-optical devices and circuits. [4] The technology for designing optical components and circuits operating at visible and NIR wavelengths has matured significantly over the last several decades, ensuring their widespread integration. While we can work toward improving data transmission rates of existing communication technology, shortage of spectral bandwidth for data transmission has become a looming problem over time. This has motivated researchers to seek out previously unused portions of the electromagnetic spectrum. The "terahertz gap" (≈30 µm-3 mm) has attracted considerable attention from researchers seeking to bridge the gap between the optical/IR and microwave spectrum. [5,6] Similar to the optical domain, the invention, optimization, and commercialization of discrete components such as sources, modulators, and detectors are necessary for the widespread use and integration of terahertz technologies. Electronic means of terahertz generation utilizing semiconductors (Si, GaAs) IMPATT [7] and Gunn diodes [8] have been developed. In conjunction with a frequency doubler/ tripler circuits, they typically operate on the lower end of the terahertz spectrum (0.1-1 THz); although the power output at higher frequency multiples might be significantly lower as compared to its fundamental mode. Additionally, InGaAs/ InP HBTs and InP HEMTs with cutoff frequencies >600 GHz have been demonstrated. [9,10] The advent of femtosecond lasers has paved the way for the generation of terahertz radiation via photoconductive switches, [11] photo-Dember effect [12,13] and nonlinear optical rectification in organic and inorganic crystals. [14][15][16] Femtosecond lasers have helped develop time domain terahertz systems that have been instrumental in ultrafast spectroscopy to study transient carrier dynamics of semiconductors. Development of terahertz quantum cascade lasers (THz-QCL) employing intersubband transitions in AlGaAs/GaAs quantum wells [17][18][19][20] is a notable milestone in terahertz lasing. In a complementary fashion, terahertz detection could be performed by electro-optic sampling in nonlinear crystals, [21] photoconductive antennas on low-temperature GaAs, [22,23] plasma wave oscillation in a field-effect channel, [24,25] etc. Finally, akin to the compact and economic components available at optical frequencies for the generation, manipulation, and detection, terahertz technology requires Terahertz waves spanning over the 0.1 to 10 THz region of the electromagnetic spectrum have attracted significant attention owing to a variety of potential applications such as short-range high-speed data transmission, noninvasive screening and detection, materials characterization, spectroscopy, etc. This has resulted in massive strides in the development of essential system components such as broadband terahertz sources, detector arrays with high responsivity, as well as...

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Role of Photoinduced Exciton in the Transient Terahertz Conductivity of Few-Layer WS₂ Laminate

Cited by 45 publications

References 54 publications

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy

Excitons in 2D perovskites for ultrafast terahertz photonic devices

2D Materials for Terahertz Modulation

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Role of Photoinduced Exciton in the Transient Terahertz Conductivity of Few-Layer WS2 Laminate

Cited by 45 publications

References 54 publications

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe2 Crystal with Time‐Resolved Terahertz Spectroscopy

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe2 Crystal with Time‐Resolved Terahertz Spectroscopy

Excitons in 2D perovskites for ultrafast terahertz photonic devices

2D Materials for Terahertz Modulation

Contact Info

Product

Resources

About

Role of Photoinduced Exciton in the Transient Terahertz Conductivity of Few-Layer WS₂ Laminate

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy

Competition between Free Carriers and Excitons Mediated by Defects Observed in Layered WSe₂ Crystal with Time‐Resolved Terahertz Spectroscopy