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Öğe Binding Energies and Optical Properties of Power-Exponential and Modified Gaussian Quantum Dots(Mdpi, 2024) Alauwaji, Ruba Mohammad; Dakhlaoui, Hassen; Algraphy, Eman; Ungan, Fatih; Wong, Bryan M.We examine the optical and electronic properties of a GaAs spherical quantum dot with a hydrogenic impurity in its center. We study two different confining potentials: (1) a modified Gaussian potential and (2) a power-exponential potential. Using the finite difference method, we solve the radial Schrodinger equation for the 1s and 1p energy levels and their probability densities and subsequently compute the optical absorption coefficient (OAC) for each confining potential using Fermi's golden rule. We discuss the role of different physical quantities influencing the behavior of the OAC, such as the structural parameters of each potential, the dipole matrix elements, and their energy separation. Our results show that modification of the structural physical parameters of each potential can enable new optoelectronic devices that can leverage inter-sub-band optical transitions.Öğe Cumhuriyet Üniversitesi Ar-Ge Strateji Belgesi (Optik, Elektro Optik ve Fotonik Teknolojileri)(2017) Başer, Pınar; Tüzemen, Ebru Şenadım; Yeşilgül, Ünal; Elagöz, Sezai; Ungan, Fatih; Köksal, Murat; Sarı, HüseyinTübitak 1000 programı tarafından desteklenen bu projenin amacı, Cumhuriyet Üniversitesi Nanofotonik Uygulama ve Araştırma Merkezinde faaliyette olan Aixtron RF200 MOCVD sistemini kullanarak III. Nesil Tandem Fotovaltaik hücrelerinin kuramsal tasarımı, büyütülmesi, fabrikasyonu ve geliştirilecek olan güneş yoğunlaştırıcı sistem ile entegrasyonunu içeren teknik proje sonucunda yüksek verimli fotovaltaik hücrelerini tamamen milli olarak üretmek için yol-harita?sını ve Ar-Ge strateji belgesini oluşturmaktır. Oluşturulacak olan strateji belgesi kapsamında yapılacak olan çalışmalar ile Ülkemiz nitelikli personel altyapısının güçlendirilmesi ve mevcut merkezlerimizin eksik altyapılarının tamamlanarak ulusal ve Uluslararası iş birliği yapabilecek ve destek verebilecek düzeye getirilmesi planlanmaktadır.Öğe The diamagnetic susceptibilities of donors in quantum wells with anisotropic effective mass(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2009) Kasapoglu, Esin; Ungan, Fatih; Sari, Hueseyin; Soekmen, IsmailThe diamagnetic susceptibility of a hydrogenic donor placed in Si, Ge and GaAs quantum wells with infinite confinement potential which have different effective mass anisotropy parameters (gamma = m(perpendicular to)L/m(parallel to)) has been investigated as a function of the well sizes. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of the effective mass approximation. It has been observed that the diamagnetic susceptibility of the donor in the anisotropic materials converges rapidly to the bulk limit as the well size increases. (C) 2009 Elsevier Ltd. All rights reserved.Öğe The effect of magnetic field on the impurity binding energy of shallow donor impurities in a Ga1-xInxNyAs1-y/GaAs quantum well(SPRINGER, 2012) Yesilgul, Unal; Ungan, Fatih; Sakiroglu, Serpil; Duque, Carlos; Mora-Ramos, Miguel; Kasapoglu, Esin; Sari, Huseyin; Sokmen, IsmailUsing a variational approach, we have investigated the effects of the magnetic field, the impurity position, and the nitrogen and indium concentrations on impurity binding energy in a Ga1-x In (x) N (y) As1-y /GaAs quantum well. Our calculations have revealed the dependence of impurity binding on the applied magnetic field, the impurity position, and the nitrogen and indium concentrations.Öğe Effect of the High-Frequency Laser Radiation on the Nonlinear Optical Properties of n-Type Double delta-Doped GaAs Quantum Wells(AMER SCIENTIFIC PUBLISHERS, 2019) Ungan, Fatih; Sari, Huseyin; Kasapoglu, Esin; Yesilgul, Unal; Sakiroglu, Serpil; Sokmen, IsmailIn the present work, the effect of non-resonant intense laser field on the nonlinear optical rectification and second and third harmonic generation of n-type double delta-doped GaAs quantum well is studied in detail. The energy eigenvalues and eigenfunctions of this structure are calculated within the framework of effective mass and envelope function approximations. Analytic formulas for the coefficients of nonlinear optical rectification and second and third harmonic generation are obtained using the compact-density matrix approach (CDMA) and iterative method. Based on this model, our obtained numerical results are reported as a function of incident photon energy for several values of non-resonant intense laser field. The results show that the coefficients of nonlinear optical rectification and second and third harmonic generation are strongly affected by the non-resonant intense laser field.Öğe Effects of an intense, high-frequency laser field on bound states in Ga1-xInxNyAs1-y/GaAs double quantum well(SPRINGER, 2012) Ungan, Fatih; Yesilgul, Unal; Sakiroglu, Serpil; Kasapoglu, Esin; Erol, Ayse; Arikan, Mehmet Cetin; Sari, Huseyin; Sokmen, IsmailWithin the envelope function approach and the effective-mass approximation, we have investigated theoretically the effect of an intense, high-frequency laser field on the bound states in a Ga (x) In1 - x N (y) As1 - y /GaAs double quantum well for different nitrogen and indium mole concentrations. The laser-dressed potential, bound states, and squared wave functions related to these bound states in Ga1 - x In (x) N (y) As1 - y /GaAs double quantum well are investigated as a function of the position and laser-dressing parameter. Our numerical results show that both intense laser field and nitrogen (indium) incorporation into the GaInNAs have strong influences on carrier localization.Öğe Effects of applied electric and magnetic fields on the nonlinear optical rectification and second-harmonic generation in a graded quantum well under intense laser field(SPRINGER, 2017) Ungan, FatihIn this present study, the effects of electric and magnetic fields on the nonlinear optical rectification and second-harmonic generation in a graded quantum well under intense laser field have been investigated theoretically. The energy eigenvalues and their corresponding eigenfunctions are obtained by solving Schrodinger equation within the framework of effective mass approximation. The analytic expressions for the optical properties are calculated by the compact-density-matrix approach and iterative method. The numerical results are presented for a typical GaAs/Ga1-xAlxAs quantum well. The results show that the nonlinear optical rectification and second-harmonic generation coefficients are considerably affected by the electromagnetic fields and intense laser field.Öğe The effects of the intense laser field on the optical properties of the asymmetric parabolic quantum well(SPRINGER, 2017) Kasapoglu, E.; Ungan, Fatih; Yesilgul, UnalWe have calculated the effects of the intense laser field on the total optical absorption coefficient (the linear and third-order nonlinear) for transition between two lower-lying electronic levels in the asymmetric parabolic GaAs/ Ga1-xAlxAs quantum well. Total absorption coefficient (linear and nonlinear absorption coefficient) for the transitions between any two electronic states was calculated by using density matrix formalism and the perturbation expansion method. Our results show that the effects of intense laser field and the well dimensions on the optical transitions are more pronounced. If well center is changed to be Lc < 0 (L-c > 0), effective well width decreases (increases) and thus we can obtain the red or blue shift in the peak position of the absorption coefficient by changing the intensities of the non-resonant intense laser field as well as dimensions of the well.Öğe 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, FatihThe 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.Öğe Exploring the Nonlinear Optical Behaviour of InGaAs/GaAs Triple Quantum Wells via Structural Modulations and External Electric Fields(Iranian Nano Society, 2023) Sayrac, Muhammed; Dakhlaoui, Hassen; Mora-Ramos, Miguel Eduardo; Ungan, FatihThe nonlinear optical properties of the InxGa1-xAs/GaAs triple quantum well structure are studied for different structure parameters and applied external electric field. Within the framework of the effective mass and envelope function approximations, the one-dimensional time-independent Schrödinger wave equation is solved using the diagonalization method to obtain the energy eigenvalues and eigenfunctions of the structure. The coefficients of nonlinear optical properties such as nonlinear optical rectification (NOR), second harmonic generation (SHG), and third harmonic generation (THG) of the structure are numerically evaluated from the corresponding expressions derived within the compact density matrix approximation. The influence of adjustable structure parameters and the applied external electric field affects the separation of subband energy levels and the magnitudes of dipole moment matrix elements. These changes in the electronic properties of the structure cause the NOR, SHG, and THG peak positions to shift towards lower or higher energy regions. It is expected that these results will enable the appropriate design of new optoelectronic devices. © (2023), (Iranian Nano Society). All Rights Reserved.Öğe 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.Öğe 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.Öğe 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, FatihThe 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.Öğe Inter-sub-band transitions and binding energies of donor impurities in a modulation-doped quantum well in the presence of electric field(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2009) Ungan, Fatih; Kasapoglu, Esin; Sari, Hueseyin; Soekmen, IsmailIn this study, we have investigated theoretically the effects of the electric field and doping concentration on the optical transitions in a modulation-doped GaAs-AlGaAs quantum well for different well widths. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of an effective-mass approximation. The electronic structure of a modulation-doped quantum well under the electric field is determined by solving the Schrodinger and Poisson equations self-consistently in the effective-mass approximation. The results obtained show that inter-sub-band transitions and the energy levels in the modulation-doped quantum well can be significantly modified and controlled by the well width and donor concentration. The sensitivity to the well widths of the absorption coefficient can be used in various optical semiconductor devices' applications. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Investigation of the Structural and Thermodynamic Parameters on the Nonlinear Optical Properties of InGaAs/InP Triple Quantum Well Exposed to an External Electric Field(Iranian Nano Society, 2023) Sayrac, Muhammed; Dakhlaoui, Hassen; Mora-Ramos, Miguel Eduardo; Ungan, FatihIn this study, the effects of both tunable physical parameters and thermodynamic variables on the linear and nonlinear optical properties of the InGaAs/InP triple quantum well are theoretically investigated in detail. In addition, the effect of an external static electric field applied parallel to the growth direction of the structure was also studied. To carry out this analysis, firstly, the energy eigenvalues and eigenfunctions of the system were obtained as a result of solving the time-independent Schrödinger equation using the diagonalization method, under the effective mass and envelope function approach. Then, using these energy eigenvalues and eigenfunctions, the nonlinear optical properties of the structure were calculated from the expressions derived within the compact density matrix approach via the iterative method. The effect of adjustable structure parameters and applied external fields affects the difference in subband energy levels at which transitions occur and the magnitudes of the dipole moment matrix elements. These changes in the electronic properties of the structure cause the peak positions of the total (linear plus nonlinear) optical absorption coefficient and total relative refractive index change coefficient (RRIC) to shift towards lower or higher energy regions. These results are expected to enable the proper design of new optoelectronic devices. © (2023), (Iranian Nano Society). All Rights Reserved.Öğe 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.Öğe Magneto-optical specifications of Rosen-Morse quantum dot with screw dislocation(Wiley, 2020) Bahar, Mustafa Kemal; Ungan, FatihThis is the first study to consider a quantum dot with screw dislocation that has Rosen-Morse (RM) confinement potential, generated by a GaAs/GaAlAs heterostructure. An external magnetic field and Aharonov-Bohm (AB) flux field were also applied on RM quantum dot (RMQD) in order to stave the effects of a screw dislocation defect. The combined effect of the screw dislocation defect, the external magnetic field, and AB flux field on the total refractive index changes (TRICs) and the total absorption coefficients (TACs) of RMQD are thus investigated. Cylindrical coordinates are used due to the direction of application of the torsion and the external fields, as well as due to the structure's symmetry. The effective mass approximation and tridiagonal matrix methods are used in order to obtain the subband energy spectra and electronic wave functions of RMQD. The nonlinear optical specifications of RMQD are checked using compact-density-matrix formalism within the framework of the iterative method. Reviews without screw dislocation are also carried out in order to be able to clarify the effects of a screw dislocation defect on the optical properties, and then, both cases are deliberated. This study is the first attempt to analyze the AB flux field for RMQD without screw dislocation. In the present study, the influences of a screw dislocation defect on RMQD's TRICs and TACs are probed by considering different values of the external magnetic field and AB flux field, and the ranges of corresponding parameters on the optimum of the structure are specified. Moreover, the study also elucidates how to rule out the effects of screw dislocation on optical specifications by means of the external fields. Despite a certain screw dislocation, the frequency range is determined where the structure behaves as if it is perfect (namely, without screw dislocation) for its optimum, which in turn is crucial for experimental applications.Öğe Modeling of electronic spectra and optical responses of a semiconductor AlGaAs/GaAs quantum well with three-step barriers: the role of external perturbations and impurity(Springer Heidelberg, 2024) Haghighatzadeh, Azadeh; Attarzadeh, Amin; Salman Durmuslar, Aysevil; Bahadir, A. l Emre; Ungan, FatihMulti-quantum barriers are of great importance in band engineering technologies and optoelectronics as they can build up quantum confinement via enhanced barrier heights. This theoretical study comprehensively investigated intersubband electronic and optical properties of an AlGaAs-based quantum well with three-step barriers. The electronic studies were performed within envelope wave functions and effective mass approximations under non-perturbative theory with hydrogenic donor impurity. The linear and the third-order nonlinear optical absorption coefficients and relative refractive index changes were examined under density matrix formalism taking into account a two-level system. Calculations were complicated to explore the role of externally applied static electric, magnetic and intense laser fields, and the donor impurity. The results showed an enhancement in the transition energies with incrementing all three external perturbations which is more impressive in the presence of a centrally positioned donor impurity. In the continue, the binding energies of donor impurity showed different affectability in the presence of external fields and the position of donor impurity. The binding energies were also found to be bigger as the donor impurity was localized at the highest probability of electron wave function. A blue-shift was detected in intersubband optical responses by enhancing all three applied fields in the presence and absence of donor impurity. The optical characteristics exhibited strongly decreased magnitudes after the addition of central impurity atom in both the presence and the absence of externally applied fields. Our findings provide a platform to design nonlinear devices for potential applications in optoelectronic technologies.Öğe Nonlinear optical properties of asymmetric n-type double delta-doped GaAs quantum well under intense laser field? (vol 90, 162, 2017)(SPRINGER, 2018) Sari, Huseyin; Kasapoglu, Esin; Yesilgul, Unal; Sakiroglu, Serpil; Ungan, Fatih; Sokmen, Ismail…Öğe Nonlinear optical properties of n-type asymmetric double ?-doped quantum wells: role of high-frequency laser radiation, doping concentration and well width(Springer Heidelberg, 2020) Durmuslar, Aysevil Salman; Eduardo Mora-Ramos, Miguel; Ungan, FatihA numerical investigation on the nonlinear optical rectification, second and third harmonic generation coefficients in asymmetric double n-type d-doped GaAs quantum well is performed in order to identify the influence of non-resonant intense laser radiation, doping concentration and the change in well widths. The energy eigenvalues and the corresponding eigenfunctions are determined by using effective-mass and parabolic band approximations. The working analytical expressions for the optical coefficients are derived from the iterative solving of compact-density matrix description of dielectric susceptibility. The obtained results reveal that the position and amplitude of the nonlinear optical rectification, second and third harmonic generation coefficients can be altered by modifying the external field as well as the compositional and geometrical setups.
