Yazar "Mese, Ali Ihsan" seçeneğine göre listele

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    Calculation of Intradonor Normalized Transition Energy in Spherical Quantum Dots Made of Different Materials
    (Wiley-V C H Verlag Gmbh, 2023) Mese, Ali Ihsan; Cicek, Engin; Ozkapi, Sena Guler; Ozkapi, Baris; Erdogan, Ilhan
    Under the effective mass approximation, the binding energies, transition energies between 1s and 1p states, and normalized transition energies of spherical quantum dots made of different materials are calculated using the variational method. In particular, binding, transition, and normalized transition energies are examined depending on the radius of the quantum dot and the position of the hydrogenic impurity. It is observed that the binding energy and transition energy decrease as the radius of the quantum dot increases, whereas the normalized transition energy increases. In all four different structures, it is seen that the binding energy first reaches a maximum and then starts to decrease according to the position of the hydrogenic impurity. In contrast, the transition energy behaves almost the opposite. Additionally, when the change of the normalized transition energy is examined according to the impurity position, it is determined that it decreases up to the value of r(i)/R = 0.6 and then remains almost constant. According to our literature review, the normalized transition energy for the four different quantum dots is calculated for the first time in this study.
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    Effect of Si and Ge doping on electronic structure of InP nanowire
    (Natl Inst Optoelectronics, 2023) Ozkapi, Sena Guler; Ozkapi, Baris; Mese, Ali Ihsan; Erdogan, Ilhan
    We present a study on the effect of Si and Ge doping on the electronic and atomic structure of Indium Phosphide nanowires using first principles calculations. Hydrogen passivated InP nanowires in zinc blende structure with 1.5 nanometers diameter [111] growth direction are considered. The results show that the substitutional Si and Ge dopings narrow the band gap of InP nanowires, and these nanowires are direct band gap semiconductors. The Si doping shifts the VBM and CBM to the lower energy levels, and this energy decrease is less in the Ge doped nanowire. PDOS analyses show that VBM and CBM occur mainly from the p orbitals of the In and P atoms. Electronic states at the Fermi level for doped nanowires are compatible with the donor levels that appear in the band structure.
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    Self-Polarization of Hydrogenic Impurity in Quantum Wells Made of Different Materials
    (Wiley-V C H Verlag Gmbh, 2022) Ozkapi, Baris; Mese, Ali Ihsan; Cicek, Engin; Erdogan, Ilhan
    The effect of the external electric field on the ground state binding energy and self-polarization of a hydrogenic donor impurity in quantum wells (QWs) made of different materials is calculated within the effective mass approximation using a variational scheme. The variations of binding energy and self-polarization depending on well width, electric field, and impurity position have been studied in detail. For each QW made of different materials, it has been observed that the binding energy decreases with the increase of the electric field, whereas the self-polarization increases. Also, it has been observed that InP/In1-x Ga x P has higher binding energy values among the structures discussed. It is seen that material selection has a noticeable effect on self-polarization and binding energy in QW-based structures.
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    Semi-analytical model of Hall resistance anomalies (overshooting) in the fractional quantized Hall effect
    (Springer, 2013) Salman, Aysevil; Mese, Ali Ihsan; Yucel, Melike Behiye; Siddiki, Afif
    We predict resistance anomalies to be observed at high-mobility two-dimensional electron systems (2DESs) in the fractional quantized Hall regime, where the narrow (L < 10 mu m) Hall bar is defined by top gates. A semi-analytic calculation scheme is used to describe the formation of integral and fractional incompressible strips. We incorporate the screening properties of the 2DES, together with the effects of perpendicular magnetic field, to calculate the effective widths of the current carrying channels. The many-body effects are included to our calculation scheme via the energy gap obtained from the well-accepted formulation of the composite fermions. We show that the fractional incompressible strips at the edges, assuming different filling factors, become evanescent and can co-exist in certain magnetic field intervals yielding an overshoot at the Hall resistance, similar to that of the integral quantized Hall effect. We also provide a mechanism to explain the absence of 1/3 state in Fabry-Perot type interference experiments. A gate defined narrow sample design is proposed to enhance the visibility of fragile effects like interference and overshooting based on our semi-analytical model.