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Öğe Analysis of surface states and series resistance in Au/n-Si Schottky diodes with insulator layer using current-voltage and admittance-voltage characteristics(Pergamon-Elsevier Science Ltd, 2009) Altındal, Şemsettin; Yücedağ, İbrahim; Tataroğlu, AdemIn order to good interpret the experimentally observed Au/n-Si (metal-semiconductor) Schottky diodes with thin insulator layer (18 angstrom) parameters such as the zero-bias barrier height (Phi(bo)), ideality factor (n), series resistance (R-s) and surface states have been investigated using current-voltage (I-V), capacitance-frequency (C-f) and conductance-frequency (G-f) techniques. The forward and reverse bias I-V characteristics of Au/n-Si (MS) Schottky diode were measured at room temperature. In addition, C-f and G-f characteristics were measured in the frequency range of 1 kHz-1 MHz. The higher values of C and G at low frequencies were attributed to the insulator layer and surface states. Under intermediate forward bias, the semi-logarithmic Ln (I)-V plot shows a good linear region. From this region, the slope and the intercept of this plot on the current axis allow to determine the ideality factor (n). the zero-barrier height (Phi(bo)) and the saturation current (I-s) evaluated to 2.878, 0.652 and 3.61 x 10(-7) A, respectively. The diode shows non-ideal I-V behavior with ideality factor greater than unity. This behavior can be attributed to the interfacial insulator layer, the surface states, series resistance and the formation barrier inhomogeneity at metal-semiconductor interface. From the C-f and G-f characteristics, the energy distribution of surface states (N-ss) and their relaxation time (tau) have been determined in the energy range of (E-c-0.493E(v))-(E-c-0.610) eV taking into account the forward bias I-V data. The values of N-ss and tau change from 9.35 x 10(13) eV(-1) cm(-2) to 2.73 x 10(13) eV(-1) cm(-2) and 1.75 x 10(-5) s to 4.50 x 10(-4) s, respectively. (C) 2009 Elsevier Ltd. All rights reserved.Öğe ASSOCIATION RULE FOR CLASSIFICATION OF BREAST CANCER PATIENTS(Yildiz Technical Univ, 2017) Pala, Tuba; Yücedağ, İbrahim; Biberoğlu, HasanData mining studies carried out on medical databases are very important in order to make an effective medical diagnosis. The purpose of data mining is to extract information from databases, to define clear and understandable patterns. In this study, an approach was presented to generate association rules on the data of breast cancer patients. Apriori algorithm is used for the extract of the rules. Apriori algorithm is usually used for the market - basket analysis. Apriori algorithm is used to determine customer shopping profiles or to campaign, in order to catch the shopping patterns. In this study, apriori algorithm was used in the extraction of the rules within the medical data. UC-Irvine archive repository of machine learning datasets [1] - Breast Cancer dataset has been studied. This dataset, including 9 attribute and 1 class atribute. It consists of records of 286 patients with 10 attributes. The study was carried out by using the Weka data mining program.Öğe Characterization of Surface States and Their Relaxation Time in Al/ZnO/p-GaAs Structure by Admittance Method at Room Temperature(Amer Scientific Publishers, 2019) Demir, Gülçin Ersöz; Yücedağ, İbrahim; Yerişkin, Seçkin AltındalSurface state (N-ss) density and their relaxation time (tau) of the fabricated Al/ZnO/p-GaAs structure was investigated in frequency range of 1 kHz-1 MHz and in voltage range of +/- 1.2 V. It was found that the variance of capacitance (C) and conductance (G/omega) with frequency and voltage is basically different especially at low and intermediate frequencies in depletion and accumulation regions. Characteristics of Al/ZnO/p-GaAs structure are affected by parameters such as N-ss, dipole and surface polarization in depletion region at low frequencies, while they are affected by parameters such as interfacial ZnO layer and series resistance (R-s) in accumulation region at higher frequencies. C and G have higher values in low frequency region due to effects such as N-ss in metal-semiconductor interface, interfacial ZnO layer and surface dipole polarization. The rise in C and G has been showed up thanks to the ac signal that can be easily monitored N-ss, strong interface and dipole polarizations, interfacial layer especially at weak inversion and depletion regions. Due to special distribution of N-ss at ZnO/p-GaAs interface, parallel conductance (G(p/omega)) - ln(f) plots show a peak under distinct voltage. Thus, the values of N-ss and omega were determined from the peak values of these plots and changed from 3.92 X 10(12) eV(-1) . cm(2) to 4.33 X 10(12) eV(1) . cm(2) and 6.3 X 10(5) s to 6.3X 10(6) s for 0.35 V and 1.1 V, respectively. These values of N-ss and 1.30 nm RMS roughness (from Atomic Force Microscopy (AFM) image) are very suitable for an electronic device.Öğe A comparative electric and dielectric properties of Al/p-Si structures with undoped and Co-doped interfacial PVA layer(Elsevier Sci Ltd, 2014) Kaya, Ahmet; Yücedağ, İbrahim; Tecimer, Hüseyin; Altındal, ŞemsettinIn this study, Al/p-Si structures with undoped and Co-doped PVA interfacial layer called S-1 and S-2 were fabricated and their both electrical and dielectric properties were compared by using 300 kHz capacitance voltage (C-V) and conductance voltage (G/omega-V) measurements at room temperature. Experimental results show that both C and G or dielectric constant (epsilon'), dielectric loss (epsilon '') values were found as strongly function of applied bias voltage especially at inverse and accumulation bias regions. It was found that the value of R-5 considerably decreases with doping Co metal contrary to conductivity especially in the forward bias region. Such behavior can be attributed to the lack of free charges in pure PVA. The imaginary parr of dielectric modulus (M '') gives Two peaks for S-1 corresponding To enough reverse and forward biases and passes from a minimum at about zero bias. Also, it is clear That the minimum of The M '' for S-2 coincides with The maximum of The for S-1 at zero bias. As a result, Co-doped PVA considerable improved The performance of structure. In addition, loss Tangent. (tan delta), ac conductivity (sigma(ac)) and real part. of The electric modulus (M') were obtained and compared each other. (C) 2014 Elsevier Ltd. All rights reserved,Öğe Comparative investigation of electronic parameters of low voltage organic field-effect transistors with variable capacitance non-ionic gel gate dielectrics(Elsevier, 2019) Yardım, Tayfun; Yücedağ, İbrahim; Allı, Sema; Allı, Abdulkadir; Demir, Ahmet; Kösemen, ArifNon-ionic gel dielectrics (NIGDs) have high effective capacitances (C-EFF) which can be used to reduce the operating voltage of the organic field-effect transistors (OFETs). Limited work has been carried out about these kinds of dielectrics although they have advantages of low cost and easy production. Besides, by mixing propylene carbonate (PC) with various kinds of polymers in order to tune the C-EFF of the blend, electronic parameter performance of the OFETs can be improved. In this study, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) based OFETs were fabricated. Specifying the poly(methyl-acrylate) (PMA) as a reference dielectric and adjusting the soybean oil to methyl acrylate weight ratio in the polymerization process to form copolymers of PMA, totally three types of dielectrics were synthesized and transformed into a gel state to obtain the reduced C-EFF. Gel dielectrics were named according to the soybean oil to methyl acrylate weight ratio. Such that, %0 ratio stands for NIGDO, %8 ratio stands for NIGD1 and %11 ratio stands for NIGD2 and OFETs fabricated with these NIGDs were named with regard to these names (NIGOFET0, NIGOFET1, and NIGOFET2). After the electrical characterization, it was seen that mobility enhanced as the C-EFF decreased as predicted. It could be attributed to a formation of less self-localization of the charge carriers in the semiconductor-dielectric interface. Moreover, it was seen that NIGOFET1 had the lowest Subthreshold Swing (SS) and off-current (I-OFF) consequently the highest on-to-off current ratio (I-ON/I-OFF). It implied that it had better insulation property and semiconductor-dielectric interface compared to the other NIGOFETs.Öğe Comparative study of the temperature-dependent dielectric properties of Au/PPy/n-Si (MPS)-type Schottky barrier diodes(Korean Physical Soc, 2015) Gümüş, Ahmet; Ersöz, Gülçin; Yücedağ, İbrahim; Bayrakdar, Sümeyye; Altındal, ŞemsettinThe dielectric properties of Au/PPy/n-Si metal-polymer-semiconductor (MPS)-type Schottky barrier diodes (SBDs) were investigated by using capacitance-voltage (C-V) and conductancevoltage (G/omega-V) measurements at various temperatures and voltages at frequencies of 100 kHz and 500 kHz. Both the real and the imaginary parts of the complex dielectric constant and dielectric loss (epsilon', epsilon aEuro(3)) and of the electric modulus (M', MaEuro(3)), as well as the conductivity (sigma (ac) ), were found to depend strongly on the temperature and the voltage. Both the C and G/omega values increased with increasing applied voltage and had inversion, depletion, and accumulation regions as with a metal-insulator-semiconductor (MIS) type behavior. Both the dielectric constant (epsilon') and the dielectric loss (epsilon aEuro(3)) increased with increasing temperature and decreased with increasing frequency. The loss tangent (tan delta) vs. temperature curve had a peak at about 200 K for both frequencies. The M' and the MaEuro(3) values decreased with increasing temperature and became independent of the frequency at high temperatures. The series resistance (R (s) ) of the diode decreased with increasing temperature for the two frequencies while the sigma (ac) increased. Such behaviors of the dielectric properties with temperature were attributed to the restructuring and reordering of charges at interface states/traps due to the varying temperature, the interfacial polarization, and the interfacial polymer layer. ln(sigma (ac) ) vs. q/kT plots had two distinct linear regions with different slopes for the two frequencies. Such behaviors of these plots confirmed the existence of two different conduction mechanisms corresponding to low and high temperatures. The values of the activation energy (E (a) ) were obtained from the slopes of these plots, and its value at low temperatures was considerably lower than that at high temperatures.Öğe A Comparative Study on the Main Electrical Parameters of Au/n-Si, Au/Biphenyl-CuPc/n-Si/ and Au/Biphenylsubs-CoPc/n-Si/ Type Schottky Barrier Diodes(Amer Scientific Publishers, 2016) Demir, Ahmet; Yücedağ, İbrahim; Ersöz, Gülçin; Altındal, Şemsettin; Baraz, Nalan; Kandaz, MehmetWe have produced Au/n-Si (MS), Au/n-Si/biphenyl-CuPc (MPS1), and Au/n-Si/biphenylSubs-CoPc (MPS2) type Schottky barrier diodes (SBDs) to investigate the effect of interfacial layer on the main electrical parameters. Biphenyl-CuPc and biphenylSubs-CoPc interfacial layers were successfully coated on n-Si substrate by using the spin coating system. The current-voltage (I-V) characteristics of these structures were investigated at room temperature and they were considerably influenced by the interfacial layer. The main electronic parameters of these three type diodes that are reverse saturation current (I-0), series resistance (R-s), ideality factor (n), and zero-bias barrier height (Phi(B0)) were determined from the forward bias I-V characteristic. The energy density distribution profile of the interface states (N-ss) was also obtained from the forward I-V data by taking into account voltage dependent effective barrier height (Phi(theta)) and ideality factor n(V), and increased from the bottom of conductance band to the mid-gap energy of Si almost exponentially. In addition, the voltage dependent profile of resistance was obtained from capacitance-voltage (C-V) and conductance-voltage (G/omega - V) data at high frequency (500 kHz) at room temperature for each diode. Experimental results show that the R-s, N-ss and the interfacial layer are significantly effective on the electrical characteristics.Öğe Comparison of Electronic Parameters of Low Voltage Organic Field-Effect Transistors with Novel Gel Gate Insulators(Amer Scientific Publishers, 2019) Yardım, Tayfun; Demir, Ahmet; Allı, Sema; Allı, Abdulkadir; Kösemen, Arif; Yücedağ, İbrahimIn this paper, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based low voltage organic field-effect transistors (OFETs) with three kinds of non-ionic gel gate insulators (NIGIs) were fabricated and compared in terms of their electronic properties. One of the NIGI was prepared by mixing solution-processed poly(methyl acrylate) (PMA) with propylene carbonate (PC) until it becoming a gel state and same procedure was applied to the solution-processed copolymers of PMA called as P18 and P28. As a result, it was seen that fabricated OFETs could be operated at low voltages which is very significant property in order to manipulate the devices in low power electronic applications. On the other hand, it was noted that mobilities of the transistors were enhanced by reducing the effective capacitance (EC) of the NIGIs. This could be attributed to less charge carrier self-localization formation between the insulator-semiconductor interface when the EC was decreased. Furthermore, devices showed similar on-to-off current (I-ON/I-OFF) ratio which was good for using them in inverter applications. Besides, subthreshold swing (SS) for the P18 non-ionic gel OFET (NIGOFET) was the highest probably due to the less water-repellent chemical structure of the P18 NIGI.Öğe Controlling the electrical characteristics of Au/n-Si structure with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature(Wiley, 2017) Baraz, Nalan; Yücedağ, İbrahim; Demir, Ahmet; Demir, Gülçin Ersöz; Altındal, Şemsettin; Kandaz, MehmetIn order to interpret well whether or not the organic or polymer interfacial layer is effective on performance of the conventional Au/n-Si (metal semiconductor [MS]) type Schottky barrier diodes (SBDs), in respect to ideality factor (n), leakage current, rectifying rate (RR), series and shunt resistances (R-s, R-sh) and surface states (N-ss) at room temperature, both Au/biphenyl-CoPc/n-Si (MPS1) and Au/OHSubs-ZnPc/n-Si (MPS2) type SBDs were fabricated. The electrical characteristics of these devices have been investigated and compared by using forward and reverse bias current-voltage (I-V) characteristics in the voltage range of (-4V)-(4V) for with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature. The main electrical parameters of these diodes such as reverse saturation current (I-0), ideality factor (n), zero-bias barrier height (phi(B0)), RR, R-s and R-sh were found as 1.14x10(-5)A, 5.8, 0.6eV, 362, 44 and 15.9k for reference sample (MS), 7.05x10(-10)A, 3.8, 0.84eV, 2360, 115 and 270k for MPS1 and 2.16x10(-7)A, 4.8, 0.7eV, 3903, 62 and 242k for MPS2, respectively. It is clear that all of these parameters considerably change by using an organic interfacial layer. The energy density distribution profile of N-ss was found for each sample by taking into account the voltage dependence of effective barrier height (phi(e)) and ideality factor, and they were compared. Experimental results confirmed that the use of biphenyl-CoPc and OHSubs-ZnPc interfacial layer has led to an important increase in the performance of the conventional of MS type SBD. Copyright (c) 2015 John Wiley & Sons, Ltd.Öğe Cuff-Less Continuous Blood Pressure Estimation from Electrocardiogram(ECG) and Photoplethysmography (PPG) Signals with Artificial Neural Network(Ieee, 2018) Şentürk, Ümit; Yücedağ, İbrahim; Polat, KemalContinuous blood measurement important information about the health status of the individuals. Conventional methods use a cuff for blood pressure measurement and cannot be measured continuously. In this study, we proposed a system that estimates systolic blood pressure (SP) and diastolic blood pressure (DP) for each heart beat by extracting attributes from ECG and PPG signals. Simultaneous ECG and PPG signals from the PhysioNet Database are pre-processed (denoising, artifact cleaning and baseline wandering) to remove noise and artifacts and segmented into R-R peaks. For each heartbeat, 22-time domain features were extracted from ECG and PPG signals. SP and DP values were estimated by introducing these 22 attributes to the model of Lavenberg-Marquardt artificial neural networks (ANN). Arterial blood pressure (ABP) was also taken from the PhysioNet MIMIC II database along with ECG and PPG signals. ABP signals have been used as targets in the artificial neural network. The system performance has been evaluated by calculating the difference between the estimated ABP values and the actual by the ANN model. The performance value between the predicted SP and actual SP values is -0.14 +/- 2.55 (mean +/- standard deviation) and the performance value between estimated DP and actual DP values is -0.004 +/- 1.6. The obtained results have shown that the proposed model has predicted blood pressure with high accuracy. In this study, SP and DP values can also be measured directly without any calibration in blood pressure estimation.Öğe Customer Churn Prediction Using Machine Learning Methods: A Comparative Analysis(Institute of Electrical and Electronics Engineers Inc., 2021) Karamollaoğlu, Hamdullah; Yücedağ, İbrahim; Doğru, İbrahim AlperCustomer churn analysis is the process of predicting customers who tend to cancel the service (subscription) they receive for various reasons, especially in sectors such as telecommunications, finance and insurance, and determining the necessary operational steps to prevent this cancellation. The study used two separate datasets from kaggle.com to identify customers who tend to unsubscribe in the telecommunications industry. The analysis process was carried out by applying machine learning methods such as Logistic Regression, K-Nearest Neighbor, Decision Trees, Random Forest, Support Vector Machines, AdaBoost, Multi-Layer Sensors and Naive Bayes methods on the relevant datasets. It was seen that the most successful method in the customer loss analysis performed on both datasets was the Random Forest method. © 2021 IEEEÖğe Determination of Type and Quality of Hazelnut using Image Processing Techniques(Ieee, 2015) Bayrakdar, Sümeyye; Çomak, Bekir; Başol, Derya; Yücedağ, İbrahimHazelnut (Corylus avellana L.) comes number two after almond in the ranking of hard shelled fruits that is cultivated commonly in the world. According to the FAO (Food and Agriculture Organization) statistics, Turkey covers approximately 70% of the world hazelnut production, and 82% of the hazelnut exportation. These statistics indicate that Turkey is the first largest hazelnut producer and exporter in the world. Quality and automation have a great importance in the agricultural industry that put our country forward as world-wide leader. In the quality control systems, classification studies with image processing methods have accelerated in recent years. In this study, it is aimed that determination of type and quality of shelled hazelnuts with image processing by using size and shape characteristics of hazelnuts. As a result of studies on a variety of hazelnuts, it was reached 84% accuracy rate for grouping of shelled hazelnut according to the type and commercial definitions. The quality of hazelnuts also was acquired without error. Inshell Hazelnut Standard (TS 3074) that is published by the Turkish Standards Institute (TSE) is based for shelled hazelnuts.Öğe Determining electrical and dielectric parameters of Al/ZnS-PVA/p-Si (MPS) structures in wide range of temperature and voltage(Springer, 2018) Baraz, Nalan; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Altındal, ŞemsettinIn this study zinc sulphide (ZnS) nanostructures have been prepared by microwave-assisted method in presence of polyvinyl alcohol (PVA) as a capping agent. The structural and morphological properties of prepared sample have been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). These analyses confirm that the sample has nano structure. They have been used this sample to fabrication of Al/ZnS-PVA/p-Si structure. The effect of temperature and voltage on the electrical and dielectric parameters of the Al/ZnS-PVA/p-Si (MPS) structures has been investigated in the wide range of temperature (140-340 K) and voltage (- 2 V to + 4 V) using capacitance/conductance-voltage (C/G-V) measurements at 500 kHz. Experimental measurements revealed that the values of C/G-V increase with increasing temperature but the values of series resistance (R (s) ) increase with decreasing temperature. As well as the dielectric parameters such as the values of real and imaginary parts of the dielectric constants (epsilon' and epsilon aEuro(3)) and electric modules (M' and MaEuro(3)), loss tangent (tan delta), and ac electrical conductivity (sigma (ac) ) were obtained using C and G/omega data. These parameters are found out as strong functions of temperature and voltage. While the values of epsilon', epsilon aEuro(3) and tan delta increase with increasing temperature, the values of sigma (ac) , M' and MaEuro(3) decrease. The Arrhenius plot (ln(sigma(ac)) vs q/kT) shows two distinct linear ranges with different slopes or activation energies (E (a) ) at low (140-230 K) and high (260-340 K) temperatures. Both values of R (s) and (ZnS-PVA) interfacial layers are also very effective parameters on the electric and dielectric properties.Öğe Determining electrical and dielectric parameters of dependence as function of frequencies in Al/ZnS-PVA/p-Si (MPS) structures(Springer, 2017) Baraz, Nalan; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Altındal, ŞemsettinWe have studied electrical and dielectric parameters of the Al/ZnS-PVA/p-Si structures using admittance measurements. For this aim, capacitance/conductance-voltage (C/G-V) measurements were performed in the frequency range of 10 kHz-5 MHz and voltages (+/- 4 V) by 50 mV steps at 300 K. Experimental results confirmed that both electric and dielectric parameters are strong function of frequency and voltage and they are especially influenced from series resistance (R-s), surface states (N-ss) and polarization processes. The values of R-s and N-ss which are obtained from the Nicollian and Brews and Hill-Coleman method, respectively, and they are decrease with increasing frequency almost as exponentially. In addition, the values of real and imaginary part of the dielectric constants (epsilon' and epsilon '') and electric modules (M' and M ''), loss tangent (tan delta), and ac electrical conductivity (sigma(ac)) were obtained using C and G/omega data as function of applied bias voltage and they are found to a strong functions of frequency. While the values of epsilon', epsilon '', and tand increase with increasing frequency, M' and rac decrease. Moreover, the epsilon', epsilon '', tand, and rac increase with applied bias voltage, whereas the M' decreases with increasing applied bias voltage. The M '' versus V plot shows a peak and its position shifts to the right with increasing bias voltage and it disappears at high frequencies. As a result, the change in the epsilon', epsilon '', tan delta, M', M '' and rac is a result of restructuring and reordering of charges at the (ZnS-PVA)/p-Si interface under an external electric field or voltage and interface polarization.Öğe Developing an CNC lathe augmented reality application for industrial maintanance training(Institute of Electrical and Electronics Engineers Inc., 2018) Güler, Osman; Yücedağ, İbrahimIn this study, developing an augmented reality training application for CNC (computer numerical control) lathe looms for industrial maintenance and repair training was described. The content has been developed for the CNC LATHE TEARS module, which is trained in the field of Machine Technologies to be operated on mobile like smart phone, tablet, etc. devices. First a training scenario was prepared for the development of the application. Then three dimensional model of a CNC lathe was modelled. Models designed to develop the augmented reality application have been transferred to the Unity3D game engine software, and using the Vuforia plug-in, a marker-based augmented reality application has been developed to work on android operating system based mobile devices like smartphone, tablet, etc. It is considered that using the developed application in the training of the students of the Machine Technologies Area in the institutions providing vocational and technical education in the official and private institutions affiliated to the Ministry of National Education, motivation of the students and the success rates of the courses will increase. At the same time, the developed application will provide facilitate the training of the users, increase the quality in production and faster maintenance and installation. © 2018 IEEE.Öğe Developing an CNC lathe augmented reality application for industrial maintanance training(Ieee, 2018) Güler, Osman; Yücedağ, İbrahimIn this study, developing an augmented reality training application for CNC (computer numerical control) lathe looms for industrial maintenance and repair training was described. The content has been developed for the CNC LATHE TEARS module, which is trained in the field of Machine Technologies to be operated on mobile like smart phone, tablet, etc. devices. First a training scenario was prepared for the development of the application. Then three dimensional model of a CNC lathe was modelled. Models designed to develop the augmented reality application have been transferred to the Unity3D game engine software, and using the Vuforia plug-in, a marker-based augmented reality application has been developed to work on android operating system based mobile devices like smartphone, tablet, etc. It is considered that using the developed application in the training of the students of the Machine Technologies Area in the institutions providing vocational and technical education in the official and private institutions affiliated to the Ministry of National Education, motivation of the students and the success rates of the courses will increase. At the same time, the developed application will provide facilitate the training of the users, increase the quality in production and faster maintenance and installation.Öğe Developing and modeling of voice control system for prosthetic robot arm in medical systems(Elsevier Science Bv, 2018) Gündoğdu, Köksal; Bayrakdar, Sümeyye; Yücedağ, İbrahimIn parallel with the development of technology, various control methods are also developed. Voice control system is one of these control methods. In this study, an effective modelling upon mathematical models used in the literature is performed, and a voice control system is developed in order to control prosthetic robot arms. The developed control system has been applied on four-jointed RRRR robot arm. Implementation tests were performed on the designed system. As a result of the tests; it has been observed that the technique utilized in our system achieves about 11% more efficient voice recognition than currently used techniques in the literature. With the improved mathematical modelling, it has been shown that voice commands could be effectively used for controlling the prosthetic robot arm. (C) 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.Öğe Dielectric properties and electric modulus of Au/PPy/n-Si (MPS) type Schottky barrier diodes (SBDS) as a function of frequency and applied bias voltage(World Scientific Publ Co Pte Ltd, 2015) Yücedağ, İbrahim; Ersöz, Gülçin; Gümüş, Ahmet; Altındal, ŞemsettinAu/PPy/n-Si Schottky barrier diodes (SBDs) were fabricated by forming polypyrrole (PPy) organic layer on n-Si using the spin coating technique. Frequency-dependent dielectric constant (epsilon'), dielectric loss (epsilon ''), loss tangent (tan delta), real and imaginary parts of electrical modulus (M' and M '') and AC electrical conductivity (sigma(ac)) parameters of the structure were investigated in the frequency range of 10-500 kHz. It was found that the values of the epsilon', epsilon '' and tan delta, in general, decrease with increasing frequency while an increase is observed in sigma(ac), M' and M ''. The tan delta and M '' also exhibit a peak at about zero-bias voltage, while peak intensity weakens with increasing frequency. The values of epsilon' and M' decrease with increasing voltage while an increase is observed in epsilon '', tan delta sigma(ac) and M ''. These changes in epsilon', epsilon '', tan delta, M', M '' and sigma(ac) values was attributed to surface charge polarization and the particular density distribution of surface states localized at PPy/n-Si interface.Öğe Dinamik kompanzasyon cihazlarında kullanılan evirici yapıları: STATCOM ve DSTATCOM topolojileri(2016) Ertay, Muhammed Mustafa; Dijle, Melek; Yücedağ, İbrahimStatik Senkron Kompanzatör (STATCOM) iletim hatlarında reaktif güç kompanzasyonu ve güç sistemi kararlılığının artırılması için kullanılmaktadır. STATCOM dağıtım hatlarında kullanılırsa dağıtım STATCOM (DSTATCOM) olarak isimlendirilmektedir. Özel bir güç aygıtı olan DSTATCOM, dağıtım sistemlerinde güç kalitesi sorunlarını çözmek için kullanılan ortak kuplaj noktasına şönt bağlı bir gerilim kaynaklı eviricidir. Evirici STATCOM ve DSTATCOM'un temel yapı birimidir. Literatürde önerilen ve gerçek uygulamalarda kullanılan birçok evirici yapıları mevcuttur. Bu makalede, bugüne kadar STATCOM ve DSTATCOM'da kullanılan evirici yapıları incelenmektedir. Evirici yapılarının avantaj ve dezavantajları ortaya konulmaktadır. Ayrıca literatürden birçok örnek verilmektedir.Öğe Electric and Dielectric Properties of Au/ZnS-PVA/n-Si (MPS) Structures in the Frequency Range of 10-200 kHz(Springer, 2017) Baraz, Nalan; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Demir, Gülçin Ersöz; Orak, İkram; Altındal, Şemsettin; Akbari, HosseinPure polyvinyl alcohol (PVA) capped ZnS semiconductor nanocrystals were prepared by microwave-assisted method, and the optical and structural properties of the as-prepared materials were characterized by x-ray diffraction (XRD) and Ultraviolet-visible (UV-Vis) techniques. The XRD pattern shows the formation of ZnS nanocrystals, and the UV-Vis spectroscopy results show a blue shift of about 1.2 eV in its band gap due to the confinement of very small nanostructures. The concentration of donor atoms (N (D)), diffusion potential (V (D)), Fermi energy level (E (F)), and barrier height (I broken vertical bar(B) (C-V)) values were obtained from the reverse bias C (-2)-V plots for each frequency. The voltage dependent profile of series resistance (R (s)) and surface states (N (ss)) were also obtained using admittance and low-high frequency methods, respectively. R (s)-V and N (ss)-V plots both have distinctive peaks in the depletion region due to the spatial distribution charge at the surface states. The effect of R (s) and interfacial layer on the C-V and G/omega-V characteristics was found remarkable at high frequencies. Therefore, the high frequency C-V and G/omega-V plots were corrected to eliminate the effect of R (s). The real and imaginary parts of dielectric constant (epsilon' and epsilon aEuro(3)) and electric modulus (M' and MaEuro(3)), loss tangent (tan delta), and ac electrical conductivity (sigma (ac)) were also obtained using C and G/omega data and it was found that these parameters are indeed strong functions of frequency and applied bias voltage. Experimental results confirmed that the N (ss), R (s) , and interfacial layer of the MPS structure are important parameters that strongly influence both the electrical and dielectric properties. The low values of N (ss) (similar to 10(9) eV(-1) cm(-2)) and the value of dielectric constant (epsilon' = 1.3) of ZnS-PVA interfacial layer even at 10 kHz are very suitable for electronic devices when compared with the SiO2. These results confirmed that the ZnS-PVA considerably improves the performance of Au/n-Si (MS) structure and also allow it to work as a capacitor, which stores electric charges or energy.
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