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Öğe Analysis of temperature dependent electrical properties of Au/perylene-diimide/n-Si Schottky diodes(ELSEVIER SCIENCE SA, 2013) Yuksel, O. F.; Tugluoglu, N.; Safak, H.; Nalcacigil, Z.; Kus, M.; Karadeniz, S.The electrical properties of Au/perylene-diimide/n-Si Schottky diode have been determined by means of current-voltage measurements in the temperature range of 75-300 K. These devices showed good rectifying behavior and the temperature dependence of the current-voltage characteristics could be explained by thermionic emission mechanism. The experimental values of barrier height and ideality factor for device have been calculated as 0.168 eV and 7.63 eV at 75 K and 0.690 eV and 1.57 eV at 300 K, respectively. The fabricated Schottky diode shows non-ideal current-voltage behavior and so it is thought that the device have a metal-interface layer-semiconductor configuration. In addition to current-voltage measurements, the room temperature capacitance-voltage characteristics of Au/perylene-diimide/n-Si devices were also investigated. The barrier height value of 1.051 eV obtained from the capacitance-voltage measurements was found to be higher than that of 0.690 eV obtained from the current-voltage measurements at room temperature. Furthermore, the energy distribution of the interface state density determined from current-voltage characteristics increases exponentially with bias from 8.01 x 10(12) eV(-1) cm(-2) at ( E-c - 0.666) eV to 5.86 x 10(13) eV(-1) cm(-2) at (E-c - 0.575) eV. (C) 2013 Elsevier B. V. All rights reserved.Öğe A detailed analysis of current-voltage characteristics of Au/perylene-monoimide/n-Si Schottky barrier diodes over a wide temperature range(AMER INST PHYSICS, 2011) Yuksel, O. F.; Kus, M.; Simsir, N.; Safak, H.; Sahin, M.; Yenel, E.The current-voltage characteristics of Au/perylene-monoimide (PMI)/n-Si Schottky device have been investigated at a wide temperature range between 75 and 300 K in detail. The measured current-voltage (I-V) characteristics of the device show a good rectification behavior at all temperatures. The electronic parameters such as the ideality factor and the barrier height are determined from the experimental data using standard current-voltage analysis method and also temperature dependence of these parameters is analyzed. In addition to the standard analysis, using the Cheung and Cheung method, the series resistance and some other electrical properties are calculated for the device, and a good agreement is obtained between relevant diode parameters. It was observed that Au/PMI/n-Si Schottky diodes exhibit space charge limited (SCL) conduction at all temperatures. Therefore, we have analyzed this SCL current mechanism in more detail. From this analysis, several electronic parameters related with the SCL mechanism are determined, and it is found that Poole-Frenkel effect is dominant in reverse bias. (C) 2011 American Institute of Physics. [doi:10.1063/1.3610394]Öğe Electrical properties of Au/perylene-monoimide/p-Si Schottky diode(ELSEVIER SCIENCE SA, 2013) Yuksel, O. F.; Tugluoglu, N.; Gulveren, B.; Safak, H.; Kus, M.In this work, we have fabricated an Au/perylene-monoimide (PMI)/p-Si Schottky barrier diode. We have investigated how electrical and interface characteristics like current-voltage characteristics (I-V), ideality factor (n), barrier height (Phi(B)) and series resistance (R-s) of diode change with temperature over a wide range of 100-300 K. Detailed analysis on the electrical properties of structure is performed by assuming the standard thermionic emission (TE) model. Possible mechanisms such as image force lowering, generation-recombination processes and interface states which cause deviations of n values from the unity have been discussed. Cheung-Cheung method is also employed to analysis the current-voltage characteristics and a good agreement is observed between the results. It is shown that the electronic properties of Schottky diode are very sensitive to the modification of perylene-monoimide (PMI) interlayer organic material and also to the temperature. The ideality factor was found to decrease and the barrier height to increase with increasing temperature. The temperature dependence of barrier height shows that the Schottky barrier height is inhomogeneous in nature at the interface. Such inhomogeneous behavior was explained on the basis of thermionic emission mechanism by assuming the existence of a Gaussian distribution of barrier heights. (c) 2013 Elsevier B.V. All rights reserved.Öğe Excitonic effects on the nonlinear optical properties of small quantum dots(IOP PUBLISHING LTD, 2008) Karabulut, I.; Safak, H.; Tomak, M.The excitonic effects on the nonlinear optical properties of small quantum dots with a semiparabolic confining potential are studied under the density matrix formalism. First, within the framework of the strong confinement approximation, we present the excitonic states and then calculate the excitonic effects on the nonlinear optical properties, such as second harmonic generation, third harmonic generation, nonlinear absorption coefficient and refractive index changes. We find the explicit analytical expressions between the corresponding nonlinear optical properties with and without considering the excitonic effects. It is seen that these analytical expressions are related only to ratios of the effective masses of electron and hole. These explicit expressions indicate that the excitonic effects on the corresponding nonlinear optical properties become more important with increasing orders of the optical susceptibilities. In addition, we suggest a scaling rule for the nth-order susceptibility as gamma((n+1)/2). The effect of the confining potential frequency on the corresponding nonlinear optical properties is also studied. Our results show a remarkable dependence of nonlinear optical properties on both the excitonic effects and the confining potential frequency.Öğe Frequency dependent interface state properties of a Schottky device based on perylene-monoimide deposited on n-type silicon by spin coating technique(ELSEVIER SCI LTD, 2013) Tugluoglu, N.; Yuksel, O. F.; Karadeniz, S.; Safak, H.We have reported a detailed investigation of frequency dependent properties of the Au/perylene-monoimide (PMI)/n-Si Schottky diodes in this study. Schottky diodes based on PMI have been fabricated by spin coating method. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics have been measured in the frequency range from 30 kHz to 1 MHz at room temperature. The values of measured capacitance C-m and conductance G(m) under both reverse and forward bias have been corrected for the effect of series resistance to obtain the real diode capacitance and the conductance values. The density of interface states (D-it) distribution profiles as a function of frequency has been extracted from the corrected C-V and G-V measurements. Interface trap states of the PMI/n-Si Schottky device have decreased by increasing the applied frequency and were found to be 8.13 x 10(11) and 1.75 x 10(11) eV(-1) cm(-2) for 30 kHz and 1 MHz, respectively. (C) 2013 Elsevier Ltd. All rights reserved.Öğe Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a quantum box with finite confining potential(ELSEVIER, 2006) Unlu, S.; Karabulut, I.; Safak, H.In this work, both the intersubband optical absorption coefficients and the refractive index changes are calculated exactly in a quantum box. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using the compact-density matrix approach. Numerical results are presented for typical GaAs/AlxGa1-xAs quantum box system. The linear, third-order nonlinear and total absorption and refractive index changes are investigated as a function of the incident optical intensity and structure parameters such as box-edge length and stoichiometric ratio. Our results show that both the incident optical intensity and the structure parameters have a great effect on the total absorption and refractive index changes. (c) 2006 Elsevier B.V. All rights reserved.Öğe Linear and nonlinear intersubband optical absorptions in an asymmetric rectangular quantum well(SPRINGER, 2007) Karabulut, I.; Atav, U.; Safak, H.; Tomak, M.The linear and nonlinear intersubband optical absorptions in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum well are studied within the framework of the density matrix formalism. We have calculated the electron energy levels and the envelope wave functions using the effective mass approach. In addition, we have obtained an expression for saturation intensity. It is shown that the parameters such as asymmetry and width of potential well not only shift the peak positions in absorption spectrum but also considerably modify their height. These results suggest that the absorption process can be easily controlled by the structure parameters of an asymmetric rectangular quantum well. Also, the incident optical intensity has a great effect on the total absorption spectrum. We have seen that the absorption peak is reduced by half when the optical intensity is approximately 0.8 MW/cm(2) for well width L = 90 angstrom and beta = 0.5. Moreover, it is seen that the saturation intensity is quite sensitive to the structure parameters of an asymmetric rectangular quantum well. Thus, the results presented here can be useful for electro-optical modulators and photodetectors in the infrared region.Öğe The modification of Schottky barrier height of Au/p-Si Schottky devices by perylene-diimide(AMER INST PHYSICS, 2013) Yuksel, O. F.; Tugluoglu, N.; Safak, H.; Kus, M.Perylene-diimide (PDI) thin film was fabricated by spin coating method on p-Si single-crystal substrate to prepare Au/PDI/p-Si Schottky device. The electrical properties of the Au/PDI/p-Si Schottky device were investigated by current-voltage (I-V) measurements in the temperature range 80-300K and room temperature capacitance-voltage (C-V) measurement. Results showed a rectification behavior. Junction parameters such as ideality factor (n), barrier height (phi(B0)), series resistance (R-s) interface state density (N-ss), built-in potential (V-bi), carrier concentration (N-A), and the width of the depletion layer (W-D) were obtained from the I-V and C-V measurements. The values of ideality factor (n) and barrier height (BH) for the Au/PDI/p-Si structure from the I-V measurements were obtained as 1.77 and 0.584 eV at 300 K, 7.78 and 0.176 eV at 80 K, respectively. It was seen that the BH value of 0.584 eV calculated for the Au/PDI/p-Si structure was significantly larger than the value of 0.34 eV of conventional Au/p-Si Schottky diodes at room temperature. Thus, modification of the interfacial potential barrier for Au/p-Si diodes has been achieved using a thin interlayer of the peryleen-diimide organic semiconductor; this has been ascribed to the fact that the peryleen-diimide interlayer increases the effective barrier height because of the interface dipole induced by passivation of the organic layer. Furthermore, the energy distribution of the interface state density determined from I-V characteristics increases exponentially with bias from 1.11 x 10(12) eV(-1) cm(-2) at (0: 556 - E-v) eV to 11.01 x 10(13) eV(-1) cm(-2) at (0:449 - E-v) eV. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789021]Öğe Oscillator strengths for the intersubband transitions in a CdS-SiO2 quantum dot with hydrogenic impurity(ELSEVIER SCIENCE BV, 2007) Yilmaz, S.; Safak, H.In this study, we have calculated the oscillator strengths for intersubband electronic transitions associated with an on-center impurity in a spherical quantum dot. Numerical calculations have been performed for both infinite confinement case and for different finite confining potential values in a spherical CdS/SiO2 quantum dot. Also, for comparison purpose, oscillator strengths for a spherical ZnS/SiO2 quantum dot with an infinite confinement potential are evaluated. (c) 2006 Elsevier B.V. All rights reserved.
