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    The double Gaussian distribution of inhomogeneous barrier heights in the organic-on-inorganic Schottky devices
    (WILEY-V C H VERLAG GMBH, 2012) Tugluoglu, Nihat; Yuksel, O. Faruk; Safak, Haluk; Karadeniz, Serdar
    We have fabricated an Au/perylene-monoimide (PMI)/n-Si organic-on-inorganic Schottky device by spin coating of PMI solution on an n-Si semiconductor wafer. Current-voltage (I-V) measurements on the device in the temperature range of 75-300K were carried out. An abnormal decrease in the experimental barrier height Phi(B) and an increase in the ideality factor n with a decrease in temperature have been observed. This behaviour has been explained on the basis of thermionic emission theory with a double Gaussian distribution of the barrier heights due to the barrier height inhomogeneities. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Intersubband resonant enhancement of the nonlinear optical properties in compositionally asymmetric and interdiffused quantum wells
    (AMER INST PHYSICS, 2008) Karabulut, Ibrahim; Safak, Haluk; Tomak, Mehmet
    We report the resonant enhancement of the second- and third-order optical nonlinearities in compositionally asymmetric quantum wells with finite confining potential and interdiffused quantum wells. The energy levels and the envelope wave functions in quantum wells are obtained by solving numerically the Schrodinger equation. The optical rectification, second and third harmonic generation coefficients are calculated within the framework of the density matrix formalism. The effect of the structure parameters such as the well width and the barrier height on the nonlinear optical properties is investigated in detail. The resulting nonlinear susceptibilities obtained in both quantum wells are considerably larger than those of bulk GaAs. (C) 2008 American Institute of Physics.
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    PHOTOIONIZATION CROSS-SECTION AND OSCILLATOR STRENGTH OF HYDROGENIC IMPURITIES IN ZnS/SiO2 QUANTUM DOTS
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2009) Yilmaz, Sait; Safak, Haluk
    In this study, the photoionization cross-section and oscillator strength for the inter-subband electronic transitions associated with a non-center impurity in the ZnS/SiO2 spherical quantum dot have been calculated. The effect of dot radius, the normalized photon energy and the potential barrier height on the cross-section have been investigated. In the calculations,both the infinite and finite confinement cases have been considered.
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    Second harmonic generation in an asymmetric rectangular quantum well under hydrostatic pressure
    (ELSEVIER SCIENCE BV, 2007) Karabulut, Ibrahim; Atav, Ulfet; Safak, Haluk; Tomak, Mehmet
    The effects of structure parameters and hydrostatic pressure oil the electronic states and the second harmonic generation (SHG) susceptibility of asymmetric rectangular quantum Well (ARQW) are studied. The asymmetry of the potential can be controlled by changing the structural parameters and this adjustable asymmetry is important for optimizing the SHG susceptibility. We have calculated analytically the electronic states in ARQW within the framework of the envelope function approach. Numerical results for Al-x/Ga1-x/As/GaAs/AlxrGa1-xr. As quantum well are presented. The results obtained show that the hydrostatic pressure and the structure parameters of ARQW significantly influence the SHG susceptibility. This behavior in the SHG susceptibility gives a new degree of freedom in regions of interest for device applications. (c) 2007 Elsevier B.V. All rights reserved.
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    Theoretical investigation of intersubband nonlinear optical rectification in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells
    (WILEY-V C H VERLAG GMBH, 2007) Karabulut, Ibrahim; Atav, Uelfet; Safak, Haluk; Tomak, Mehmet
    In this study, a theoretical investigation of intersubband nonlinear optical rectification in Alx1Ga1-x1As/ GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells is presented. The electronic states in the asymmetric rectangular quantum well are described within the framework of the envelope function approach including the effects of band nonparabolicity and the effective mass mismatch. The nonlinear optical rectification is calculated using the density matrix formalism. It is found that the nonlinear optical rectification in the asymmetric rectangular quantum well depends sensitively on the parameters such as the width and the asymmetry of the potential well. The adjustable parameters allow for tuning of the asymmetric rectangular quantum well system to the desired wavelength while retaining a large optical rectification coefficient. This gives a new degree of freedom in various device applications based on nonlinear optical properties. Band nonparabolicity is found to significantly influence both electronic states and nonlinear optical rectification. Moreover the resulting optical rectification coefficient is much larger than the ones for bulk GaAs and some other theoretical studies in literature. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.