Browsing by Author "Kutlu, E."
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Item Open Access Ab initio study of electronic properties of armchair graphene nanoribbons passivated with heavy metal elements(Elsevier, 2019) Narin, P.; Abbas, J. M.; Atmaca, G.; Kutlu, E.; Lisesivdin, S. B.; Özbay, EkmelIn this study, electronic properties of graphene nanoribbons with armchair edges (AGNRs) have been investigated with Density Functional Theory (DFT). Effects of heavy metal (HM) elements, including Zinc (Zn), Cadmium (Cd) and Mercury (Hg) atoms on electronic behavior of AGNRs have been calculated by passivating for both one and two edges of AGNRs in detail. To explain the electronic behavior of investigated AGNRs, the electronic band structure, the density of states (DOS), total energy have been calculated. Energetically favorable structures have been determined using calculated binding energy values. The obtained bandgap values of investigated structures changes between 0.30 and 0.64 eV. Increasing atomic number of passivation atoms have led to an increment in the bandgap of AGNRs.Item Open Access Effect of substitutional as impurity on electrical and optical properties of β-Si3N4 structure(Elsevier Ltd, 2016) Kutlu, E.; Narin, P.; Atmaca, G.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, Ekmelβ-Si3N4 is used as the gate dielectric for surface passivation in GaN-based, high-electron mobility transistors(HEMTs). In this study, the electrical and optical characteristics of the hexagonal β-Si3N4 crystal structure were calculated using density functional theory (DFT) and local-density approximation (LDA). Calculations of the electronic band structure and the density of states (DOS) were made for the pure β-Si3N4 crystal structure and the β-Si3N4 crystal doped with an arsenic (As) impurity atom. In addition, the optical properties such as the static dielectric constant, refractive index, extinction coefficient, absorption coefficient and reflection coefficient were examined depending on the photon energy. As a result of these calculations, it was observed that the As impurity atom drastically changed the electrical and optical properties of the pure β-Si3N4 crystalline structure, and improvements are suggested for potential further studies.Item Open Access Electronic and optical properties of black phosphorus doped with Au, Sn and I atoms(Taylor and Francis, 2018) Kutlu, E.; Narin, P.; Lisesivdin, S. B.; Özbay, EkmelIn this study, the electronic and the optical properties of monolayer black phosphorus (BP) doped with Gold (Au), Tin (Sn) and Iodine (I) atoms have been investigated by the density-functional theory (DFT) method. In the calculations, the electronic and the optical properties of monolayer BP have been substantially changed with doping. Monolayer BP has a narrow bandgap as 0.85 eV, BP doped with these atoms, results in a metallic behaviour and nearly spin gapless band gap behaviour. The dielectric constant of BP which shows anisotropic optical properties due to different edge states as zigzag and armchair has been changed with doping especially with Au.Item Open Access Electronic properties of graphene nanoribbons doped with zinc, cadmium, mercury atoms(Elsevier B.V., 2018) Ömeroğlu, O.; Kutlu, E.; Narin, P.; Lisesivdin, S. B.; Özbay, EkmelThe effect of substitutional impurities as Zinc (Zn), Cadmium (Cd) and Mercury (Hg) on electronic properties of graphene nanoribbons (GNRs) was investigated by using Density Functional Theory (DFT). A substantial change in the electronic properties of GNR structures was observed while changing the position of dopant atom from the edge to the center of armchair graphene nanoribbons (AGNRs) and zigzag graphene nanoribbons (ZGNRs). The calculations are shown that the electronic band gap of GNRs can be controlled depending on the position of dopant atoms. The calculated electronic band structures for both AGNRs and ZGNRs show spin-dependent metallic or semiconductor behavior according to the position of dopant atoms. From the Density of States (DOS) information, quasi-zero-dimensional (Q0D) and quasi-one-dimensional (Q1D) type behaviors are observed. It is shown that because the doped ZGNRs had the lowest total energies, ZGNRs are energetically more stable than AGNRs.Item Open Access Electronic properties of Li-doped zigzag graphene nanoribbons(Elsevier B.V., 2016) Narin, P.; Kutlu, E.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, EkmelZigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom.Item Open Access Electronic properties of zigzag ZnO nanoribbons with hydrogen and magnesium passivations(Elsevier, 2018) Abbas, J. M..; Narin, P.; Kutlu, E.; Lisesivdin, S. B.; Özbay, EkmelIn this study, the electronic properties of ZnO nanoribbons with zigzag edges (ZZnONr) have been investigated with Density Functional Theory (DFT). After a geometric optimization, the electronic band structures, the density of states (DOS) of ZZnONr passivated with Hydrogen (H) and Magnesium (Mg) atoms were calculated ZZnONr. It is shown that the increasing width of ZZnONrs has led to a decrement in energy band gap of the studied structures. While ZZnONr passivated with Mg for Zn-rich edge have not been shown a spin dependency, the structure passivated with Mg for O-rich edge have exhibited spin-dependent band structure. The energetically most stable structures have been determined as ZZnONr passivated with Mg for Zn-rich edge. ZZnONr passivated with Mg atoms for both edges have a graphene-like band structure especially for 8 and 10 atom width structures and this property of ZZnONrs could be important in terms of the electron transport for ZZnONrs.Item Open Access Electronic structure of β-Si3N4 crystals with substitutional icosagen group impurities(National Institute of Optoelectronics, 2017) Kutlu, E.; Narin, P.; Atmaca, G.; Sarıkavak-Lişesivdin, B.; Lişesivdin, S. B.; Özbay, EkmelThe β-Si3N4 crystals are widely used in industrial and electronics areas. Therefore, β-Si3N4 has drawn the attention of researchers for many years. In this study, effects of icosagen group impurity atoms in the IIIA group on the electronic properties of the β-Si3N4 crystal were analyzed by using the density functional theory. As a result of these analyses, it was determined that the electronic properties of the crystal change significantly. Basic electronic characteristics for pure β-Si3N4 crystal and icosagen group impurity β-Si3N4 crystals, such as band structures, densities of states, binding energies, and formation energies were investigated. We identified that the band gap of the β-Si3N4 crystal was affected significantly by the impurity, and this change was varying linearly in line with the formation energy for the impurity cases. As a result of calculations, the Al-impurity was found to be the lowest-energy impurity state.Item Open Access A first principles investigation of the effect of aluminum, gallium and indium impurities on optical properties of β-Si3N4 structure(Elsevier GmbH, 2017) Narin, P.; Kutlu, E.; Atmaca, G.; Lişesivdin, S. B.; Özbay, EkmelIn this study, effects of some impurity atoms included in IIIA group such as Al, Ga, and In on the optical properties of the β-Si3N4 structure have been discussed. The calculations were made using Density Functional Theory (DFT) in 0–15 eV range and local density approximation (LDA) as the exchange-correlation. Using the real and the imaginary parts of the complex dielectric function, the basic optical properties of β-Si3N4 such as dielectric coefficient, refractive index, absorption, reflection coefficients have been investigated. As a result of the calculations, it is determined that optical properties of structure have been significantly changed with doping.Item Unknown Negative differential resistance observation and a new fitting model for electron drift velocity in GaN-based heterostructures(Institute of Electrical and Electronics Engineers, 2018) Atmaca, G.; Narin, P.; Kutlu, E.; Malin, T. V.; Mansurov, V. G.; Zhuravlev, K. S.; Lişesivdin, S. B.; Özbay, EkmelThe aim of this paper is an investigation of electric field-dependent drift velocity characteristics for Al0.3Ga0.7N/AlN/GaN heterostructures without and with in situ Si3N4 passivation. The nanosecond-pulsed current-voltage ( {I}-{V} ) measurements were performed using a 20-ns applied pulse. Electron drift velocity depending on the electric field was obtained from the {I}-{V} measurements. These measurements show that a reduction in peak electron velocity from \text {2.01} \times \text {10}^{\text {7}} to \text {1.39} \times \text {10}^{\text {7}} cm/s after in situ Si3N4 passivation. Also, negative differential resistance regime was observed which begins at lower fields with the implementation of in situ Si3N4 passivation. In our samples, the electric field dependence of drift velocity was measured over 400 kV/cm due to smaller sample lengths. Then, a well-known fitting model was fitted to our experimental results. This fitting model was improved in order to provide an adequate description of the field dependence of drift velocity. It gives reasonable agreement with the experimental drift velocity data up to 475 kV/cm of the electric field and could be used in the device simulators.