Analytical Calculation of Exciton Binding Energy, Quasi-Particle Band Gap and Optical Gap in Strained Mono-layer MoS2

Ahmad, Shahzad; Zubair, Muhammad; Jalil, Osama; Ang, Kah Wee; Younis, Usman

doi:10.1007/s11664-020-08719-1

Cited by 9 publications

(9 citation statements)

References 34 publications

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“…It should be mentioned here that CVD-MoS 2 2D crystals are tensile-strained due to a thermal expansion mismatch between a SiO 2 /Si substrate and MoS 2 in the cooling procedure of CVD. Tensile strains cause modifications of the conductivity and valence band profiles of 2D MoS 2 due to strained exciton binding energies, leading to changes of the A and B excitons and the trion component as well as of the whole spectrum. − Over the surface of CVD-MoS 2 sheets, residual tensile strains are known to be highly uneven, and at the same time, thicker flakes might be less relaxed. Therefore, possibly, varying residual tensile strains might be responsible for the unusual thickness-dependent changes of the trion binging energy and the spectral weight observed in CVD-grown 2D MoS 2 .…”

Section: Results and Discussionmentioning

confidence: 99%

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

et al. 2021

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The behavior of the trion and exciton photoluminescence (PL) under various laser excitation conditions, that is, energy and power, is studied in monolayer and few-layer (FL) chemical vapor deposition (CVD)-MoS2 flakes grown on SiO2/Si. The room-temperature μ-PL spectroscopy of the flakes shows that the A exciton at 1.86 eV is overlapped by the trion component. First, the thickness-dependent characterization of the flakes has been carried out. The trion spectral weight and dissociation energy are observed to increase with the number of layers, which is correlated with an increase in nonequilibrium electron density. We propose the presence of many-body effects explaining this unusual dependence in CVD-MoS2 on n-type SiO2/Si. In the power-dependent μ-PL measurements, the deconvolution of spectra for the exciton and trion bands shows a faster intensification of the trion component compared to the A exciton with increasing laser power. The trion binding (dissociation) energy varied from 28 to 33 meV in the monolayer and from 32 to 46 meV in FL MoS2, when increasing the power of excitation light. The phenomenon is found to be more prominent when increasing the energy of excitation from 2.33 to 3.06 eV. The enhancement of the trion binding energy leads to a strong intensification of the trion component. Thereby, the intense A exciton/trion PL band redshifts and becomes more asymmetric when increasing the power of excitation at both energies of 2.33 or 3.06 eV. Simultaneously, the B exciton contribution to the spectrum also increases. Such an enhanced formation of the trions and B excitons is explained by a rate of photogenerated electron–hole pairs, leading to a higher population of nonequilibrium electrons. In the measurements under a higher excitation energy of 3.06 eV, the PL redshift is more prominent because the trion component is more intense compared to the A band. This is explained by considering a higher absorption of MoS2 at higher energies.

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Section: Results and Discussionmentioning

confidence: 99%

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

et al. 2021

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“…It is worth noting that the energy of the exciton calculated by the PL peak position is smaller than the electronic band gap due to the binding energy (BE) of the corresponding electron and hole pairs. 41,42 The exciton BE of a pristine TMDC has been detected to be around 27 to a few hundred meV. 43−45 Recent theoretical and experimented results have shown that the BE should not be significantly influenced by the defects in the same TMDC flakes.…”

Section: Resultsmentioning

confidence: 93%

“…The basal plane shows a typical exciton energy of 1.899 eV, which is consistent with the previous studies. , The wrinkle and edge have smaller exciton energies, which are 1.876 and 1.890 eV, respectively. It is worth noting that the energy of the exciton calculated by the PL peak position is smaller than the electronic band gap due to the binding energy (BE) of the corresponding electron and hole pairs. , The exciton BE of a pristine TMDC has been detected to be around 27 to a few hundred meV. − Recent theoretical and experimented results have shown that the BE should not be significantly influenced by the defects in the same TMDC flakes. , Accordingly, the redshift of the A peak position is attributed to the narrower local band gap on the wrinkle and edge.…”

Section: Resultsmentioning

confidence: 99%

Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides

Huang

et al. 2022

ACS Nano

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Defects can locally tailor the electronic properties of 2D materials, including the band gap and electron density, and possess the merit for optical and electronic applications. However, it is still a great challenge to realize rational defect engineering, which requires quantitative study of the effect of defects on electronic properties under ambient conditions. In this work, we employed tip-enhanced photoluminescence (TEPL) spectroscopy to obtain the PL spectra of different defects (wrinkle and edge) in mechanically exfoliated thin-layer transition metal dichalcogenides (TMDCs) with nanometer spatial resolution. We quantitatively obtained the band gap and electron density at defects by analyzing the wavelength and intensity ratio of excitons and trions. We further visualized the strain distribution across a wrinkle and the edge-induced reconstructive regions of the band gap and electron density by TEPL line scans. The doping effect on the Fermi level and optical performance was unveiled through comparative studies of edges on TMDC monolayers of different doping types. These quantitative results are vital to guide defect engineering and design and fabrication of TMDC-based optoelectronics devices.

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“…Two-dimensional transition metal dichalcogenides (TMDs), especially the monolayer MoS 2 , have attracted great research interest in their fundamental and vital applications as field effect transistors, integrated circuits, photodetectors, light-emitting diodes, and solar cells [1][2][3][4][5][6][7][8][9]. To date, it is still one of the most important research topics to manipulate the electrical and optoelectrical properties of the single-layer MoS 2 through designable patterns [10][11][12][13][14][15][16][17][18], electrical and magnetic fields [19][20][21], defects [22][23][24], and strain [25][26][27][28][29][30][31][32][33] for the novel application as electronic and optoelectronic nanodevices. Strain, among them, is regarded as an effective avenue to modulate the properties of TMD materials, as it directly affects their lattice structures and thus alters energy band structures and optical properties [23][24][25][26][27][28][29][30][31][32]…”

Section: Introductionmentioning

confidence: 99%

“…To date, it is still one of the most important research topics to manipulate the electrical and optoelectrical properties of the single-layer MoS 2 through designable patterns [10][11][12][13][14][15][16][17][18], electrical and magnetic fields [19][20][21], defects [22][23][24], and strain [25][26][27][28][29][30][31][32][33] for the novel application as electronic and optoelectronic nanodevices. Strain, among them, is regarded as an effective avenue to modulate the properties of TMD materials, as it directly affects their lattice structures and thus alters energy band structures and optical properties [23][24][25][26][27][28][29][30][31][32][33][34]. Various methods [34] have been reported to introduce strain to a 2D material, mainly including pre-treating the substrates and utilizing the mismatch between TMD materials and their underlying substrates, and so on.…”

Section: Introductionmentioning

confidence: 99%

Tuning photoluminescence behaviors in strained monolayer belt-like MoS2 crystals confined on TiO2(001) surface

et al. 2022

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We report on a monolayer (ML) MoS2 belt-like single crystal directly fabricated on the Rutile-TiO2(001) surface via chemical vapor deposition (CVD). We find that the photoluminescence (PL) behaviors in the ML MoS2 single crystal strongly depend on their shapes and the interface of MoS2/TiO2. Compared with the as-grown triangular ML MoS2, the PL peak position is in a blue shift and the PL intensity is increased for the as-grown ML MoS2 belt. Moreover, the PL peak position is in the blue shift by about 38 meV and the intensity is enhanced by nearly 15 times for the as-grown ML MoS2 belt crystal on TiO2 than those samples transferred onto SiO2/Si substrate. This special PL behavior can be attributed to the in-plane compressive strain that is introduced during the CVD growth of ML MoS2 belts confined by the substrate. The energy band of the strained ML MoS2 belt is changed with an up-shift in the conduction band minimum (VBM) and a down-shift in the valence band maximum (CBM), and the band gap is thus enlarged. This results in the energy band structural realignment in the interface of MoS2/TiO2, thereby weakening the charge transferring from the TiO2 substrate to MoS2 and suppressing the concentration of charged excitons to finally enhance the PL intensity of the ML MoS2 belt. The substrate-confined ML MoS2 belts provide a new route for tailoring light-matter interactions to upgrade their weak quantum yields and low light absorption, which can be utilized in optoelectronic and nanophotonic devices.

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Analytical Calculation of Exciton Binding Energy, Quasi-Particle Band Gap and Optical Gap in Strained Mono-layer MoS2

Cited by 9 publications

References 34 publications

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides

Tuning photoluminescence behaviors in strained monolayer belt-like MoS2 crystals confined on TiO2(001) surface

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Analytical Calculation of Exciton Binding Energy, Quasi-Particle Band Gap and Optical Gap in Strained Mono-layer MoS2

Cited by 9 publications

References 34 publications

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS2

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS2

Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides

Tuning photoluminescence behaviors in strained monolayer belt-like MoS2 crystals confined on TiO2(001) surface

Contact Info

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Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂