Anisotropic behavior of excitons in single-crystal α-SnS

Le, Van Long; Cuong, Do Duc; Nguyễn, Hoàng Tùng; Nguyen, Xuan Au; Kim, Bogyu; Kim, Kyu-Jin; Lee, Wonjun; Hong, Soon Cheol; Kim, Tae Jung; Kim, Young Dong

doi:10.1063/5.0021690

Cited by 10 publications

(13 citation statements)

References 46 publications

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“…Knowledge of the optical properties of SnS x Se 1−x is required to design and fabricate these devices efficiently and to bring them to realistic applications. Several reports have been published on the optical properties of SnS x Se 1−x [10][11][12][13][14][15][16][17][18], but only at selected compositions [16][17][18][19][20]. Knowledge of the optical properties of SnS x Se 1−x at arbitrary composition x, which can be achieved by using spectroscopic ellipsometry (SE) data with the Tauc-Lorentz (TL) modelling, where T refers to the Tauc joint density of states model and L to the Lorentz oscillator, is important for practical device applications.…”

Section: Introductionmentioning

confidence: 99%

Optical Properties of Anisotropic SnSxSe1−x for Arbitrary Compositions

Nguyen

Kim

et al. 2020

J. Korean Phys. Soc.

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Here, we report parameter values for the model dielectric function (ε = ε1 +iε2) of the SnSxSe1−x alloy in the spectral range from 0.74 to 6.4 eV and the composition range 0 ≤ x ≤ 1 by using the Tauc-Lorentz (TL) model. The experimentally reported dielectric function data for SnSxSe1−x along the zigzag (a) and the armchair (b) directions were borrowed from a previous study for selected compositions. We successfully reproduced the asymmetric nature of the dielectric function with TL lineshapes. The ε data are parameterized by using six and seven TL components for the zigzag and the armchair directions, respectively. The obtained parameters at several compositions were fit with cubic polynomials, which can be used to determine the dielectric function and the refractive index as continuous functions of the energy and the composition. Our results will be useful for optoelectronic device design based on SnSxSe1−x materials.

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Section: Introductionmentioning

confidence: 99%

Optical Properties of Anisotropic SnSxSe1−x for Arbitrary Compositions

Nguyen

Kim

et al. 2020

J. Korean Phys. Soc.

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“…Stack-layered structures materials in IV-VI group bring remarkable properties, which show high anisotropy of electrical and optical properties along with principal directions [1][2][3][4]. Strong correlation between the lattice anisotropy and optical property is indispensable information for many technological applications such as solar cells [5,6], ion batteries [7], sensors [8], thermoelectric devices [9], photovoltaics [10], and nonlinear optical applications [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…Among them, SnS is a representative material to illustrate impressive characteristics. The SnS crystallize in an orthorhombic structure belonging to the space group Pnma, which consists of valence bonds between each Sn atom and three adjacent S atoms to form a puckered honeycomb network, resulting in strong (ab-axis) in-plane anisotropy [2,14], while the SnS layers are separated by weak van der Waals bonding in the c-direction.…”

Section: Introductionmentioning

confidence: 99%

“…Complex dielectric function ε = ε 1 + iε 2 or refractive index Ñ = n + ik values provide useful insight into the electronic structure for better characterization of device performance [15]. There are many reports on the optical properties of SnS by absorption and reflection [16], photoluminescence [17], photoreflectance [18], ultraviolet-visible-near infrared spectroscopy [19], and spectroscopic ellipsometry (SE) [2,3,14]. In this work, we used the SE because it directly determines the dielectric function and refractive index of a material [20,21] without using the Kramers-Kronig relations.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we used the SE because it directly determines the dielectric function and refractive index of a material [20,21] without using the Kramers-Kronig relations. The dielectric functions of SnS along principal axes have been reported [2,3,14]. However, there has been no systematic investigation so far on the dependence of the dielectric function on the direction of azimuthal angle.…”

Section: Introductionmentioning

confidence: 99%

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Azimuthal angle dependent dielectric function of SnS by ellipsometry

Nguyen

Jung

Kim

et al. 2021

J. Korean Phys. Soc.

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Since α-SnS has optically strong anisotropic characteristics, a simple method to determine its crystal orientation is strongly needed in device engineering. In this report, by measuring dielectric function ε = ε 1 + iε 2 of α-SnS in the 1-5 eV spectral region with the full azimuthal angle range, we could find a simple relationship between measured dielectric function values and the orientation of the α-SnS crystal axis. Therefore, during the device manufacturing process, one can use spectroscopic ellipsometry to quickly measure the dielectric response of the α-SnS region of the device to correctly orient the SnS along the preferred direction for the best performance of the device. We also performed the azimuthal angle-dependent analysis of the critical points (CP) analysis, which shows that the positions of CP energies are basically invariant, while their amplitudes and lineshapes strongly depend on the azimuthal angle.

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Photoemission Study of the Thermoelectric Group IV‐VI van der Waals Crystals (GeS, SnS, and SnSe)

Tołłoczko,

Zelewski,

Ziembicki

et al. 2023

Advanced Optical Materials

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Group IV‐VI van der Waals crystals (MX, where M = Ge, Sn, and X = S, Se) are receiving increasing attention as semiconducting thermoelectric materials with nontoxic, earth‐abundant composition. Among them, SnSe is considered the most promising as it exhibits a remarkably high thermoelectric figure of merit (ZT), initially attributed to its low lattice thermal conductivity. However, it has been shown that the electronic band structure plays an equally important role in thermoelectric performance. A certain band shape, described as a “pudding mold” and characteristic for all MXs, has been predicted to significantly improve ZT by combining good electrical conductivity with high Seebeck coefficient. This subtle feature is explored experimentally for GeS, SnS, and SnSe by means of angle‐resolved photoemission spectroscopy. The technique also allows for the determination of the effective mass and Fermi level position of as‐grown undoped crystals. The findings are supported by ab initio calculations of the electronic band structure. The results greatly contribute to the general understanding of the valence band dispersion of MXs and reinforce their potential as high‐performance thermoelectric materials, additionally giving prospects for designing systems consisting of van der Waals heterostructures.

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Anisotropic behavior of excitons in single-crystal α-SnS

Cited by 10 publications

References 46 publications

Optical Properties of Anisotropic SnSxSe1−x for Arbitrary Compositions

Optical Properties of Anisotropic SnSxSe1−x for Arbitrary Compositions

Azimuthal angle dependent dielectric function of SnS by ellipsometry

Photoemission Study of the Thermoelectric Group IV‐VI van der Waals Crystals (GeS, SnS, and SnSe)

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