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Öğe A theoretical study on the optical properties of a quantum well with short-range bottomless exponential potential(World Scientific Publ Co Pte Ltd, 2019) Ungan, F.; Mora-Ramos, M. E.; Sakiroglu, S.; Sari, H.; Sokmen, I.The effects of external applied fields on the electron-related optical nonlinear properties in a short-range bottomless exponential potential quantum well are investigated. The potential profile behaves as inverse square root in the vicinity of the origin and vanishes exponentially toward infinity, supporting a finite number of bound states whose energies and wave functions are determined within the effective-mass approximation. The linear, third-order nonlinear and total optical absorption coefficients (TOACs) as well as the coefficient of relative refractive index changes (RRICs) of the system are calculated from the expressions derived in the framework of the compact density matrix approach. The results obtained after numerical calculations show that with the effect of the static electric and magnetic fields (high-frequency THz laser field), the resonant peak position of the optical response shifts toward higher (lower) energies and the magnitude of the peak increases.Öğe Barrier height effect on binding energies of shallow hydrogenic impurities in coaxial GaAs/AlxGa1-xAs quantum well wires under a uniform magnetic field(ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD, 2007) Karki, H. D.; Elagoz, S.; Baser, P.; Amca, R.; Sokmen, I.The ground state binding energies of axial hydrogenic impurities in a coaxial cylindrical quantum well wire are reported as a function of the barrier height and the radius of wire in the presence of a uniform magnetic field applied parallel to the wire axis. The quantum well wire (QWW) is assumed to be an infinitely long cylinder of GaAs material surrounded by AlxGa1-xAs (for finite case and vacuum for infinite case). Binding energy calculations were performed with the use of a variational procedure in the effective mass approximation. We observed that the binding energy is sensitive to well radius only for both larger R values and small magnetic fields. We also compared the infinite and finite case binding energies and showed that increasing the Al concentration in the finite barrier case, binding energies are increased as expected. Our results are in good agreement and complementary with the previous theoretical works. (C) 2006 Elsevier Ltd. All rights reserved.Öğe Binding energies of donor impurities in modulation-doped GaAs/AlxGa1-xAs double quantum wells under an electric field(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2009) Kasapoglu, E.; Ungan, F.; Sari, H.; Sokmen, I.In this study, we have investigated theoretically the binding energies of shallow donor impurities in modulation-doped GaAs/Al0.33Ga0.67 As double quantum wells (DQWs) under an electric field which is applied along the growth direction for different doping concentrations as a function of the impurity position. The electronic structure of modulation-doped DQWs under an electric field has been investigated by using a self-consistent calculation in the effective-mass approximation. The results obtained show that the carrier density and the depth of the quantum wells in semiconductors may be tuned by changing the doping concentration, the electric field and the structure parameters such as the well and barrier widths. This tunability gives a possibility of use in many electronic and optical devices. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Binding energy of donor impurity states and optical absorption in the Tietz-Hua quantum well under an applied electric field(ELSEVIER SCIENCE BV, 2018) Al, E. B.; Kasapoglu, E.; Sakiroglu, S.; Duque, C. A.; Sokmen, I.For a quantum well which has the Tietz-Hua potential, the ground and some excited donor impurity binding energies and the total absorption coefficients, including linear and third order nonlinear terms for the transitions between the related impurity states with respect to the structure parameters and the impurity position as well as the electric field strength are investigated. The binding energies were obtained using the effective-mass approximation within a variational scheme and the optical transitions between any two impurity states were calculated by using the density matrix formalism and the perturbation expansion method. Our results show that the effects of the electric field and the structure parameters on the optical transitions are more pronounced. So we can adjust the red or blue shift in the peak position of the absorption coefficient by changing the strength of the electric field as well as the structure parameters. (C) 2017 Elsevier B.V. All rights reserved.Öğe Binding energy of impurity states in an inverse parabolic quantum well under magnetic field(ELSEVIER SCIENCE BV, 2007) Kasapoglu, E.; Sari, H.; Sokmen, I.We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x(max) = 0.3. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions. (c) 2006 Elsevier B.V. All rights reserved.Öğe Broadband asymmetric quantum-well infrared photodetector in long-wavelength infrared range (LWIR)(IEEE, 2007) Hostut, M.; Ergun, Y.; Sokmen, I.A theoretical investigation of a GaAs-AlGaAs infrared detector consisting of three asymmetric quantum wells is presented. Each quantum well is sensitive to yield absorption and a photoresponse at peak wavelengths of 8 pro, 9.5 mu m and 10.8 mu m respectively. Device operation is based on inter-subband bound-to-bound transition. Asymmetry in the quantum welts is shown to give broad band responsivity spectrum at an operating bias.Öğe Broadband staircase quantum well infrared photodetector with low dark current(ELSEVIER SCIENCE BV, 2006) Ergun, Y.; Hostut, M.; Eker, S. U.; Sokmen, I.We present a theoretical investigation of a novel staircase-like quantum well infrared photodetector (QWIP). It detects wavelengths between 8.8 mu m and 12.3 mu m at an applied electric field of F= 6 x 10(4) V/cm at room temperature. Device operation is based on inter-subband bound to continuum transition. We also calculated the responsivity at room temperature and dark current density at 77 K. The dark current density was found to be around 10(-8) A/cm(2) at operating bias, which is lower than the conventional QWIPs in the literature. (c) 2005 Elsevier B.V. All rights reserved.Öğe Broadband staircase quantum well infrared photodetector: working in long wavelength infrared range (LWIR)(WILEY-V C H VERLAG GMBH, 2007) Hostut, M.; Kartal, D.; Ergun, Y.; Sokmen, I.; Stutzmann, MWe present a theoretical investigation of a staircase-like quantum well infrared photodetector (QWIP). it detects wavelength between 7.6 mu m and 13.5 mu m range at an applied electric field of F = 1.9x10(4) V/cm at 77 K. The dark current density was found to be around 2x10(-7) A/cm(2) at operating bias, which is lower than the conventional QWIPs in the literature. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Combined effects of intense laser field and applied electric field on exciton states in GaAs quantum wells: Transition from the single to double quantum well(WILEY-V C H VERLAG GMBH, 2012) Duque, C. A.; Mora-Ramos, M. E.; Kasapoglu, E.; Sari, H.; Sokmen, I.The effects of intense laser radiation on the exciton states in GaAs-Ga1xAlxAs quantum wells are studied with the inclusion of applied dc electric fields oriented along the growth direction of the system. The calculations are made within the effective mass and parabolic band approximations. The intense laser effects have been included along the lines of the Floquet method, modifying the confinement potential associated to the heterostructure. The results for the exciton binding energy, the energy of the exciton-related photoluminescence peak, and the carriers overlap integral are presented for several configurations of the quantum well size, the strength of the applied electric fields, and the incident laser radiation.Öğe Combined effects of intense laser field, electric and magnetic fields on the nonlinear optical properties of the step-like quantum well(ELSEVIER SCIENCE SA, 2015) Kasapoglu, E.; Duque, C. A.; Mora-Ramos, M. E.; Restrepo, R. L.; Ungan, F.; Yesilgul, U.; Sari, H.; Sokmen, I.In the present work, the effects of the intense laser field on total optical absorption coefficient (the linear and third-order nonlinear) and total refractive index change for transition between two lower-lying electronic levels in the step-like GaAs/Ga1-xAlxAs quantum well under external electric and magnetic fields are investigated. The calculations were performed within the compact density-matrix formalism with the use of the effective mass and parabolic band approximations. The obtained results show that both total absorption coefficient and refractive index change are sensitive to the well dimensions and the effects of external fields. By changing the intensities of the electric, magnetic and non-resonant intense laser fields together with the well dimensions, we can obtain the blue or red shift, without the need for the growth of many different samples. (C) 2015 Elsevier B.V. All rights reserved.Öğe Combined effects of the intense laser field, electric and magnetic fields on the optical properties of n-type double delta-doped GaAs quantum well(ELSEVIER SCIENCE BV, 2017) Sari, H.; Kasapoglu, E.; Sakiroglu, S.; Yesilgul, U.; Ungan, F.; Sokmen, I.In the present work, the effects of the non-resonant intense laser field, electric and magnetic fields on the optical properties, such as linear, third order nonlinear and the total optical absorption coefficient and refractive index changes associated with the intersubband transitions between the ground and the first excited states in the n-type double delta-doped GaAs quantum well is theoretically studied by solving the Schrodinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. Our numerical results show that the optical absorption coefficient and refractive index change are quite sensitive to the applied external fields, such as non resonant intense laser field, electric and magnetic fields. The obtained results can be applied for the design of various optoelectronic devices based on the intersubband transitions of electrons.Öğe Density of impurity states of hydrogenic impurities in an inverse parabolic quantum well under the magnetic field(ELSEVIER SCIENCE BV, 2007) Kasapoglu, E.; Sari, H.; Sokmen, I.We investigated the effects of the magnetic field on the density of impurity states in a GaAs/GaAlAs inverse parabolic quantum well (lPQW) for different Al concentrations at the well center. The calculations were performed within the effective mass approximation, using a variational method. We report in this paper the effects of the magnetic field, well width and the Al concentration at the well center on the density of states and the binding energies of the donor impurities. (c) 2006 Elsevier B.V. All rights reserved.Öğe Dependence of impurity binding energy on nitrogen and indium concentrations for shallow donors in a GaInNAs/GaAs quantum well under intense laser field(SPRINGER, 2011) Ungan, F.; Kasapoglu, E.; Sari, H.; Sokmen, I.Within the framework of the effective-mass approximation, using a variational method, we have calculated the effect of intense laser radiation on the binding energy of the shallow-donor impurities in a Ga1-xInxNyAs1-y/GaAs single quantum well for different nitrogen and indium mole concentrations. Our numerical results show that the binding energy strongly depends on the laser intensity and frequency (via the laser dressing parameter) and it also depends on the nitrogen and indium concentrations. Impurity binding energy under intense laser fields can be tuned by changing the nitrogen and indium mole fraction.Öğe Donor impurity states and related optical responses in triangular quantum dots under applied electric field(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2014) Kasapoglu, E.; Ungan, F.; Sari, H.; Sokmen, I.; Mora-Ramos, M. E.; Duque, C. A.The linear and nonlinear coefficients for the optical absorption and relative refractive index change associated with transitions between donor impurity states in a two-dimensional quantum dot of triangular shape under applied electric field are calculated for y-polarization of the incident light. Both the effective mass and parabolic band approximations have been considered. The results show that the application of a DC electric field strengthens the impurity-related optical absorption response, with particular relevance in the case of the nonlinear contribution to it. However, for a fixed donor atom position inside the triangular quantum dot, the calculations show that the in-plane orientation of the applied field can becomes a critical parameter that may lead to a strong quenching of the interstate light absorption. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Effect of exchange-correlation potential on the plasmon dispersions in a doped symmetrical double quantum well(WILEY-V C H VERLAG GMBH, 2007) Tuezemen, E. Senadim; Turkoglu, A.; Ergun, Y.; Sokmen, I.; Tanatar, B.We have calculated the plasmon dispersion relations in a doped double quantum well with and without exchange-correlation potential added to the effective potential of the system. The calculations were done for high and low doping densities by solving the Schrodinger and Poisson equations self-consistently. Our numerical results show that the exchange - correlation potential is quite important at high doping densities of donor impurities for plasmon dispersions at large wave vectors. On the other hand, the ratio of subband populations n(i) to donor density N-D is more affected at low densities. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Effect of hydrostatic pressure on interband transitions in coupled quantum wires(IOP PUBLISHING LTD, 2007) Kasapoglu, E.; Gunes, M.; Sokmen, I.We calculate the exciton binding energy and interband optical absorption in a rectangular coupled quantum wire under the hydrostatic pressure in the effective-mass approximation, using the variational approach. It is found that the interband optical absorption strongly depend on the hydrostatic pressure and the coupling parameter, and that the magnitude of the absorption coefficient for the HH1-E1 transition in the coupled quantum wire is larger than that of the single quantum wire.Öğe The effect of hydrostatic pressure on subband structure and optical transitions in modulation-doped quantum well(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2011) Ungan, F.; Yesilgul, U.; Sakiroglu, S.; Kasapoglu, E.; Sari, H.; Sokmen, I.Within the framework of effective-mass approximation, we have calculated theoretically the effects of hydrostatic pressure and doping concentration on subband structure and optical transitions in modulation-doped GaAs/Al(x)Ga(1-x)As quantum well for different well widths. The electronic structure of modulation-doped quantum well under the hydrostatic pressure is determined by solving the Schrodinger and Poisson equations self-consistently. The results obtained show that intersubband transitions and the subband energy levels in the modulation-doped quantum well can be significantly modified and controlled by the well width, donor concentration and hydrostatic pressure. (C) 2011 Elsevier Ltd. All rights reserved.Öğe Effect of intense high-frequency laser field on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a parabolic quantum well under the applied electric field(ELSEVIER SCIENCE BV, 2014) Yesilgul, U.; Ungan, F.; Sakiroglu, S.; Mora-Ramos, M. E.; Duque, C. A.; Kasapoglu, E.; Sari, H.; Sokmen, I.The effects of the intense high-frequency laser field on the optical absorption coefficients and the refractive index changes in a GaAs/GaAlAs parabolic quantum well under the applied electric field have been investigated theoretically. The electron energy levels and the envelope wave functions of the parabolic quantum well are calculated within the effective mass approximation. Analytical expressions for optical properties are obtained using the compact density-matrix approach. The numerical results show that the intense high-frequency laser field has a large effect on the optical characteristics of these structures. Also we can observe that the refractive index and absorption coefficient changes are very sensitive to the electric field in large dimension wells. Thus, this result gives a new degree of freedom in the optoelectronic device applications. (C) 2013 Elsevier B.V. All rights reserved.Öğe The effect of intense laser field on the photoionization cross-section and binding energy of shallow donor impurities in graded quantum-well wire under an electric field(IOP PUBLISHING LTD, 2006) Kasapoglu, E.; Sari, H.; Yesilgul, U.; Sokmen, I.The laser-field dependence of the impurity binding energy and donor-related photoionization cross-section in graded quantum-well wire under an external static electric field is calculated by a variational method and in the effective mass approximation. We have shown that, in the graded quantum-well wire structures, not only the 'dressed' potential but also the applied direction of the external electric field plays a very important role in the determination of the binding energy.Öğe Effect of magnetic fields on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in square and graded quantum wells(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2010) Ozturk, E.; Sokmen, I.In this study, both the intersubband optical absorption coefficients and the refractive index changes as dependent on the magnetic field are calculated in square and graded quantum wells. Our results show that the position and the magnitude of the linear and total absorption coefficients and refractive index changes depend on the magnetic field strength and the shape of potential. The incident optical intensity has a great effect on the total absorption and refractive index changes. (C) 2010 Elsevier Ltd. All rights reserved.
