Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Author: search.filters.author.Kang, JunInstitution Author: search.filters.institutionAuthor.Şahin, Hasan

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  • Article
    Citation - WoS: 17
    Citation - Scopus: 18
    Origin of Anomalous Band-Gap Bowing in Two-Dimensional Tin-Lead Mixed Perovskite Alloys
    (American Physical Society, 2021) Gao, Qiang; Şahin, Hasan; Kang, Jun; Wei, Su-Huai
    The origin of the pronounced and composition-dependent band-gap bowing in Sn/Pb mixed perovskite alloys has been under debate for a long time. Previous studies reported conflicting results on whether the chemical or structural effect is the dominant mechanism. In this paper, the band-gap bowing effect and its possible origins in recently synthesized two-dimensional (2D) Cs2PbxSn1-xI2Cl2 alloys are investigated from first-principles calculations. In agreement with experiments, a large and composition-dependent bowing coefficient is observed. By analyzing the contribution from volume deformation, charge exchange, structural relaxation, and short-range order, it is found that the dominant mechanism causing the anomalous gap bowing is the structural relaxation-induced wave-function localization, forming isovalent-defect-like states, despite the negligible octahedral distortion and small lattice mismatch between the two end compounds. This is understood by the s-p repulsion-induced strong antibonding character of the valence-band maximum which leads to a large deformation potential, thus even a small atomic displacement can result in a large shift of the energy level. These results thus highlight the critical role of strong deformation potential and structural relaxation effect in unusual band evolution of 2D Sn/Pb perovskite alloys, and can be helpful to the modulation of their band gap for optoelectronic applications.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Electronic Properties of Intrinsic Vacancies in Single-Layer Caf2 and Its Heterostructure With Monolayer Mos2
    (AIP Publishing LLC, 2021) Li, Zhenzhen; Başkurt, Mehmet; Şahin, Hasan; Gao, Shiwu; Kang, Jun
    Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF2 single layer and its heterostructures with monolayer MoS2 are investigated from first-principles calculations. V-Ca introduces a shallow defect level close to the VBM, whereas VF introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, VF has a relatively lower formation energy than VCa, except for the extreme Ca-rich case. Thus, VF should be dominant in CaF2. The band offset between CaF2 and MoS2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF2, the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF2 to MoS2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS2, and the electronic properties of MoS2 are almost intact. Compared with h-BN that has a small valence band offset with MoS2 and could introduce in-gap defect states, CaF2 can be a good candidate to serve as the dielectric layer of MoS2-based transistors. Published under an exclusive license by AIP Publishing.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Strain Tunable Band Structure of a New 2d Carbon Allotrope C-568
    (IOS Press, 2020) Gao, Qiang; Kang, Jun; Şahin, Hasan
    Recently, C(568)has emerged as a new carbon allotrope, which shows semiconducting properties with a band gap around 1 eV and has attracted much attention. In this work, the external strain effects on the electronic properties of C(568)have been studied theoretically through first-principle calculations. The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C(568)in case of tensile strain, their effects are quite different in the case of compressive strain. With increasing compressive uniaxial strain, the band gap of C(568)first increases, and then dramatically decreases. In contrast, the application of compressive biaxial strain up to -10% only leads to a slight increase of band gap. Moreover, an indirect-to-direct gap transition can be realized under both types of compressive strain. The results also show that the optical anisotropy of C(568)can be induced under uniaxial strain, while biaxial strain does not cause such an effect. These results indicate good strain tunability of the band structure of C-568, which could be helpful for the design and optimization of C-568-based nanodevices.