Bu çalışmada, özellikle optik bölgede geniş band soğurma gösteren çok tabakalı bir hiperbolik metamalzeme tasarlanmıştır. Tasarlanan yapıda üç farklı metal (Ag, Au ve Al) ve yarıiletken bir malzeme (InGaAs) kullanılmıştır. Hesaplamalarda Transfer Matris Metodundan (TMM) yararlanılmıştır. Bu yöntem kullanılarak tasarlanan çok tabakalı yapıların optik soğurma ve yansıma spektrumları gelme açısına bağlı olarak incelenmiştir. Metal-dielektrik çok tabakalı yapıların hiperbolik dispersiyon gösterdiği bölgeler belirlenmiş, ayrıca gelme açısına bağlı kontur grafikleri elde edilmiştir. Yapılan hesaplamalar sonucunda, metal olarak gümüşün kullanıldığı heteroyapının en iyi soğurma spektrumu verdiği gözlenmiştir.

The optical behaviors of molybdenum oxide thin films are highly important due to their widespread applications. In the present paper, the effect of thickness on the structure, morphology and optical properties of molybdenum oxide (MoOx) thin films prepared on Corning glass substrates using thermal evaporation technique was studied. The structure and morphology of films were characterized using Xray diffraction (XRD) and scanning electron microscopy (SEM), respectively, while their optical properties were investigated by UV-VIS-NIR spectrophotometry in the spectral range from 300 to 2500 nm. It was observed that whole films have amorphous structure and also they showed rather high transmittance values reached nearly up to 90%. Absorption analysis showed two types of electronic transitions; both direct and indirect interband transition energy values of films decrease from 4.47 to 3.45 eV and from 3.00 to 2.75 eV, respectively, with increasing the film thickness, while the width of the localized states tail increases with thickness. This decrease in the band gap value can be attributed to the rising oxygenion vacancy densities with the thickness. The refractive indices of films were calculated from Sellmeier coefficients determined by nonlinear curve fitting method based on the measured transmittance spectral data. The dispersion of the refractive index was discussed in terms of the Wemple-DiDomenico singleos-cillator model. The dispersion parameters such as average oscillator energy, E-o, the dispersion energy, E-d, and static refractive index n(o) were evaluated and they found to vary significantly with the film thickness. (C) 2015 Elsevier B.V. All rights reserved.

In this work, the perylene-monoimide/n-Si (100) Schottky structures have been fabricated by spin coating process. We have studied the capacitance–voltage (C–V) and conductance-voltage (G–V) characteristics of the Au/perylene-monoimide/n-Si diodes at 500 kHz before and after 60Co γ-ray irradiation. The effects of 60Co γ -ray irradiation on the electrical characteristics of a perylene-monoimide/n-Si Schottky diode have been investigated. A decrease both in the capacitance and conductance has been observed after 60Co γ -ray irradiation. This has been attributed to a decrease in the net ionized dopant concentration that occurred as a result of 60Co γ-ray irradiation. Some contact parameters such as barrier height (Φ B ) interface state density (N ss ) and series resistance (R s ) have been calculated from the C–V and G–V characteristics of the diode before and after irradiation. It has been observed that the Φ B and N ss values are decreased after the applied radiation, while the R s value is increased.

The optical constants of thin film prepared by cadmium hydroxide nanoparticles spray coated on the glass substrate held about at 100 degrees C temperature have been investigated using the optical transmission and reflection spectra. The transmission spectrum exhibits that the film has a high transparency (similar to 80%) at the infrared region. From standard optical analysis, direct band gap energy of Cd(OH)(2) was found as 3.13 eV, and also, it was seen that the calculated refractive index varies between 1.65 and 2.15 throughout the spectral region considered. The dispersion parameters such as oscillator energy, dispersion energy, and static and high frequency refractive index were determined in regard to the Wemple DiDomenico single oscillator model. Finally, some dielectric parameters of material such as relaxation time, dissipation (loss) factor, volume and surface energy loss functions and optical conductivity were calculated.

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 30kHz to 1MHz at room temperature. The values of measured capacitance Cm and conductance Gm 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 (Dit) 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 8.13×1011 and 1.75×1011eV−1cm−2 for 30kHz and 1MHz, respectively.

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.

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 80–300 K and room temperature capacitance-voltage (C–V) measurement. Results showed a rectification behavior. Junction parameters such as ideality factor (n), barrier height (ϕB0), series resistance (Rs) interface state density (Nss), built-in potential (Vbi), carrier concentration (NA), and the width of the depletion layer (WD) 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...

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.

Ag/perylene-monoimide(PMI)/n-GaAs Schottky diode was fabricated and the current-voltage (I-V) characteristics at a wide temperature range between 75 and 350 K and also the capacitance-voltage (C-V) characteristics at room temperature for 1 MHz have been analyzed in detail. The measured I-V characteristics exhibit a good rectification behavior at all temperature values. By using standard analysis methods, the ideality factor and the barrier height are deduced from the experimental data and also the variations of these parameters with the temperature are analyzed. In addition, by means of the Cheung and Cheung method, the series resistance and some other electrical properties are calculated for the diode. Finally, capacitance-voltage characteristics of device have been analyzed at the room temperature. From analyzing the capacitance measurements, Schottky barrier height is determined and then compared with the value which calculated from the I-V measurements at room temperature. Also, the concentration of ionized donors, built-in potential and some other parameters of diode are found using C-V characteristics. (C) 2012 Elsevier B.V. All rights reserved.

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 75–300 K were carried out. An abnormal decrease in the experimental barrier height ΦB 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.

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.

Optical absorbance measurements have been performed on the epoxy resin and the composites prepared by its modification with two different oxime derivatives (benzaldoxime and 2-furaldoxime) in the wavelength interval of 190-680 nm by unpolarized light. Using the experimental absorbance data, dielectric constant and refractive index dispersion have been determined by means of standard oscillator fit procedure. Moreover, based on the dispersion analysis, direct and indirect band gap energies of the samples have been calculated. It is found that direct band energy for epoxy is nearly 3.49 eV, while its value for the oxime derivatives has been increased up to the 4.15 eV. Another important result to be pointed out is that the absorbance for the 2-furaldoxime doped resin has been greatly increased in a respectively, narrow interval (similar to 30 nm wide) in the UV region, while in the case for the benzaldoxime doped sample, a decreasing has been observed in the absorbance at the same region. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1490-1495, 2011

In this study, we calculate the photoionization cross section and refractive-index change of an on-center hydrogenic impurity in a CdS-SiO2 spherical quantum dot. In numerical calculations, both the finite- and infinite-confinement cases are considered and a variational scheme is adopted to determine the energy eigenvalues for the impurity. The variations of the photoionization cross section with the dot radius, the refractive-index change, and the normalized photon energy are investigated, and the effect of the potential-barrier height on the cross section is discussed. The results obtained show that the photoionization cross section and the refractive-index change in CdS-SiO2 spherical quantum dots are sensitively dependent on the incident optical intensity and on the dot sizes.

In this study, the photoionization cross-section and oscillator strength for the intersubband electronic transitions associated with an on-center impurity in the ZnS / SiO 2 spherical quantum dot have been calculated. The effects 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.

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 γ(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.

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 Schrödinger 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.

Bu calismada, Optiksel Parametrik Salinim (OPO) sistemlerinde kullanilan bazi tek ve cift eksenli kristallerin temel fiziksel ve optik ozellikleri incelenmistir. Yuksek donusum kazancina sahip koherent isik elde etmek icin gereken kosullar tartisilmistir. Ayrica, faz uyum kosullarinin kristallerin cesitli parametreleriyle degisimleri incelenmistir. Numerik hesaplamalar KDP ve KTP kristalleri icin gerceklestirilmistir.

The linear and nonlinear intersubband optical absorptions in AlxlGa1-xlAs/GaAs/Alxr Ga1-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/cm2 for well width L=90 Å and β=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.

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.