Photonics / Fotonik

Permanent URI for this collectionhttps://hdl.handle.net/11147/2590

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Access Right: Closed AccessAuthor: search.filters.author.Sözen, Yiğit

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Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 8
    Citation - Scopus: 9
    Cesium Manganese Chloride: Stable Lead-Free Perovskite From Bulk To Single Layer
    (Elsevier, 2021) Sözen, Yiğit; Özen, Sercan; Şahin, Hasan
    Motivated by the recent advances in perovskite-based solar cells, here we investigate stability, electronic properties and vibrational characteristics of lead-free perovskite, CsMnCl3, and its low dimensional forms by means of first-principles calculations. Structural optimizations reveal that, regardless of whether it is bulk or ultra-thin single layer cubic perovskite structure, CsMnCl3 crystal exhibit robust antiferromagnetism in its ground state due to oppositely aligned magnetic moments of Mn atoms. In addition to total energy calculations, phonon band dispersions indicate that CsMnCl3 structure sustains its dynamical stability down to its thinnest single layer crystal structures. The calculated Raman spectrums state that while the first-order Raman scattering is forbidden for bulk CsMnCl3 due to the cubic symmetry; dimensional-reduction-driven symmetry breaking leads to emergence of experimentally-observable distinctive Raman active modes in bilayer and single-layer crystal structures. Moreover, the electronic band dispersions reveal that from its bulk to ultra-thin single layer structures CsMnCl3 crystals are robust antiferromagnetic insulators. Multiple valid features like controllable dimensionality, robust antiferromagnetism and wide electronic band gap make cubic CsMnCl3 crystal as a potential candidate for nano-scale optoelectronic applications.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 5
    Raman and Optical Characteristics of Van Der Waals Heterostructures of Single Layers of Gap and Gase: a First-Principles Study
    (Royal Society of Chemistry, 2021) Sözen, Yiğit; Şahin, Hasan
    One of the effective methods to modulate or improve the fundamental properties of 2D van der Waals materials is building their heterostructures. In this study, we employ first-principles calculations based on density functional theory to predict the ground state properties of vertically aligned single layer crystals of GaP and GaSe. First, it is shown that, depending on the intimate contact atoms in GaP, the crystal formation of heterostructures displaying characteristics of type-I and type-II heterojunctions is possible. Here, the quasiparticle bandgaps for the spatially direct and indirect electronic transitions are calculated to be 2.70 and 1.78 eV, respectively. Vibrational analysis not only reveals the dynamic stability of the heterostructures but also allows the calculation of the Raman activity spectrum of each structure, providing a fingerprint of the stacking type. In addition, by solving the BSE equation on top of G(0)W(0) approximation, the optical gaps, reflectance and transmittance spectra of the heterostructures are determined. The calculated absorption spectra demonstrate that the spectral position and characteristics of the optical transitions are altered depending on the heterojunction type. Furthermore, it is found that the interband and intraband transitions in the GaP/GaSe heterostructures can also be monitored via their reflectance and transmittance spectra.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    First-Principles Investigation of Structural, Raman and Electronic Characteristics of Single Layer Ge3n4
    (Elsevier, 2022) Yayak, Yankı Öncü; Sözen, Yiğit; Tan, Fırat; Güngen, Deniz; Gao, Q.; Kang, J.; Yağmurcukardeş, Mehmet; Şahin, Hasan
    By means of density functional theory-based first-principle calculations, the structural, vibrational and electronic properties of single-layer Ge3N4 are investigated. Structural optimizations and phonon band dispersions reveal that single-layer ultrathin form of Ge3N4 possesses a dynamically stable buckled structure with large hexagonal holes. Predicted Raman spectrum of single-layer Ge3N4 indicates that the buckled holey structure of the material exhibits distinctive vibrational features. Electronic band dispersion calculations indicate the indirect band gap semiconducting nature of single-layer Ge3N4. It is also proposed that single-layer Ge3N4 forms type-II vertical heterostructures with various planar and puckered 2D materials except for single-layer GeSe which gives rise to a type-I band alignment. Moreover, the electronic properties of single-layer Ge3N4 are investigated under applied external in-plane strain. It is shown that while the indirect gap behavior of Ge3N4 is unchanged by the applied strain, the energy band gap increases (decreases) with tensile (compressive) strain. © 2021 Elsevier B.V.