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    Electronic transmission and conductance oscillations in electrostatic multibarrier system based on graphene monolayer
    (Iop Publishing Ltd, 2023) Alsalmi, Omar H.; Dakhlaoui, Hassen; Belhadj, Walid; Ungan, Fatih
    The Landauer-Buttiker formalism and the transfer matrix method (TMM) were used to solve the Dirac equation to theoretically explore the transmission coefficient and the conductance of multibarrier graphene systems (MGS). We have addressed the impact of the number of barriers, angle of incidence, and the quantum size of different layers on the electronic properties. The obtained results show that the conductance and the transmission of the carriers can be readily modulated by increasing the number of barriers. It has been observed that an increase in the number of barriers doubles the number of resonant states which leads to the emergence of energetic minibands alternating with minigaps. Furthermore, we found that after doubling the quantum wells the number of resonant states and minigaps increase and their shapes become well defined. Moreover, we considered two cases of incidence (oblique and normal). In the normal incidence case, the structures were completely transparent for different sizes and incident energy values. However, for high angles of incidence, the transmission coefficient presented sharper resonant peaks separated by minigaps. Thereby, according to our theoretical investigations, such structures can be useful for modulating the electronic properties of devices based on electrostatic MGS.
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    GaAs Quantum Dot Confined with a Woods-Saxon Potential: Role of Structural Parameters on Binding Energy and Optical Absorption
    (Mdpi, 2023) Dakhlaoui, Hassen; Belhadj, Walid; Elabidi, Haykel; Ungan, Fatih; Wong, Bryan M.
    We present the first detailed study of optical absorption coefficients (OACs) in a GaAs quantum dot confined with a Woods-Saxon potential containing a hydrogenic impurity at its center. We use a finite difference method to solve the Schrodinger equation within the framework of the effective mass approximation. First, we compute energy levels and probability densities for different parameters governing the confining potential. We then calculate dipole matrix elements and energy differences, E1p-E1s, and discuss their role with respect to the OACs. Our findings demonstrate the important role of these parameters in tuning the OAC to enable blue or red shifts and alter its amplitude. Our simulations provide a guided path to fabricating new optoelectronic devices by adjusting the confining potential shape.
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    Harnessing a Dielectric/Plasma Photonic Crystal as an Optical Microwave Filter: Role of Defect Layers and External Magnetic Fields
    (Mdpi, 2024) Dakhlaoui, Hassen; Belhadj, Walid; Elabidi, Haykel; Al-Shameri, Najla S.; Ungan, Fatih; Wong, Bryan M.
    We investigate the transmittance spectrum of a multichannel filter composed of dielectric (A) and plasma (P) materials in the microwave region within the transfer matrix formalism. Two configurations of the proposed filter are studied under the influence of an applied magnetic field: (1) a periodic structure containing (A/P)N unit cells surrounded by air and (2) the introduction of a second dielectric material (D) acting as a defect layer to produce an (AP)N/2/D/(AP)N/2 structure. Our findings reveal that in the periodic case, the number of resonant states of the transmittance increases with number N; however, the observed blue and red shifts depend on the intensity and orientation of the applied magnetic field. We present contour plots of the transmission coefficients that show the effect of the incident angle on the shifts of the photonic band gaps. Furthermore, we find that the introduction of a defect layer generates additional resonant states and merges the central resonant peak into a miniband of resonances. Moreover, we show that the number of resonant peaks and their locations can be modulated by increasing the unit cell number, N, as well as increasing the width of the inserted defect layer. Our proposed structures enable the design of novel photonic filters using magnetized plasma materials operating in the microwave region.
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    Impacts of electric and magnetic fields on the optical and electronic characteristics of graphene- based multibarrier structure
    (Springer, 2023) Belhadj, Walid; Dakhlaoui, Hassen; Alsalmi, Omar H.; Ungan, Fatih
    The conductance and electronic transmission of Dirac electrons and holes across multibarrier Cantor-like graphene are investigated using on the transfer matrix method and Landauer-Buttiker formalism. Electric and magnetic fields are applied to the top of a monolayer graphene to generate multiple electromagnetic barriers separated by quantum wells. The impact of the magnetic and electric fields as well as the quantum size on the behavior of the transmission coefficient and conductance is discussed. The results indicate that the transmission coefficients exhibit oscillations indicating the existence of resonant states in miniband energies separated by minigap energies. This phenomenon known as the bifurcation process is more pronounced for a higher number of barriers. The behavior observed in the conductance variation reflects of the transmission coefficient especially for lower energies. Furthermore, the contour plot of the transmission coefficient shows the predominant impact of the incidence angle on the symmetry of the minigaps and minibands. These results are expected to be beneficial for experiments that improve the performance of new generations of devices based on multibarrier Cantor-like graphene systems.
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    Linear and nonlinear optical properties in GaAs quantum well based on konwent-like potential: Effects of impurities and structural parameters
    (Elsevier, 2023) Dakhlaoui, Hassen; Belhadj, Walid; Ungan, Fatih; Al-Shameri, Najla S.
    The optical absorption coefficients (OACs), refractive index changes (RICs), and electronic states in konwent-like quantum well under the effects of silicon impurities were studied within the framework of the effective mass approximation (EMA). Firstly, the subband energy levels and their probability densities are determined by solving Schrodinger-Poisson equations iteratively. Once these quantities are computed, we have addressed different OACs and RICs (linear and nonlinear) between the ground and the first excited levels. We have considered two positions of the silicon-doped layer. The first one is at the center of the structure and the second one is inside the left potential well. Our findings indicate that in the case of doping at the center, an increase in the concentration of the doped layer reduces the energy levels of the ground and the first excited states. However, when the doped layer is moved to the left well, its concentration increase augments the energy of the first excited state and diminishes that of the ground state. This behavior of energy levels and wavefunctions is attributed to the newly created triangular well around the doped layer. Moreover, the impact of the structural parameters and their impact on the red/blue shift of the (OACs) and (RICs) have been discussed in detail. As a consequence, the concentration and position of the doped layer as well as the structural parameters constitute an important tool to modify the shape of the confining potential which leads to additional control of the energy states and optical properties of different heterostructures based on konwent-like quantum wells.
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    Numerical study of optical absorption coefficients in Manning-like AlGaAs/GaAs double quantum wells: Effects of doped impurities
    (Elsevier, 2023) Dakhlaoui, Hassen; Belhadj, Walid; Durmuslar, Aysevil Salman; Ungan, F.; Abdelkader, A.
    We study the electronic and optical properties of a heterostructure based on Manning-like double quantum wells under the impact of an n-doped layer inserted in two different locations. By solving the coupled Schro & BULL;dingerPoisson equations, we have determined the four lowest energy levels and their corresponding density of probabilities. After that, we have deduced the optical absorption coefficients between the ground level and each excited state. The study addresses two locations of the doped layer. The first location is at the center of the heterostructure and the second one is at the middle of the right quantum well. The obtained findings show that the energy levels are degenerated when we dope at the center especially for low values of doping concentrations. However, by doping at the right well, we observe a lifting of degeneracy even for low concentrations of the doped layer. Our study demonstrated that the lifting of degeneracy which was absent for low concentrations in the case of doping at the center of the heterostructure can be obtained by adjusting one of the structural parameters of the Manning-like potential. Furthermore, we have discussed in detail the blue and red shifts behaviors observed in the dominant optical absorption coefficients, especially by varying the concentration of the doped layer. Our study confirms that the doping technique stills an excellent strategy to manipulate the electronic and optical properties in quantum wells based on symmetrical shapes.