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Öğe Analysis of electrical and photoelectrical properties of ZnO/p-InP heterojunction(Elsevier Science Sa, 2011) Ocak, Yusuf Selim; Kulakci, Mustafa; Turan, Rasit; Kilicoglu, Tahsin; Gullu, OmerAZnO/p-InP heterojunction has been fabricated by dc sputtering of ZnO on p-InP. It has been observed that the device has a good rectification. The electrical properties of the device such as ideality factor, barrier height, series resistance have been calculated using its current-voltage (I-V) measurements between 300 and 380K with 20K intervals. The short current density (J(sc)) and open circuit voltage (V-oc) parameters have been determined between 40 and 100mW/cm(2). The photovoltaic parameters of the device have been also determined under 100mW/cm(2) and AM1.5 illumination condition. (C) 2011 Elsevier B.V. All rights reserved.Öğe Barrier height enhancement of metal/semiconductor contact by an enzyme biofilm interlayer(Taylor & Francis Ltd, 2013) Ocak, Yusuf Selim; Guven, Reyhan Gul; Tombak, Ahmet; Kilicoglu, Tahsin; Guven, Kemal; Dogru, MehmetA metal/interlayer/semiconductor (Al/enzyme/p-Si) MIS device was fabricated using -amylase enzyme as a thin biofilm interlayer. It was observed that the device showed an excellent rectifying behavior and the barrier height value of 0.78eV for Al/-amylase/p-Si was meaningfully larger than the one of 0.58eV for conventional Al/p-Si metal/semiconductor (MS) contact. Enhancement of the interfacial potential barrier of Al/p-Si MS diode was realized using enzyme interlayer by influencing the space charge region of Si semiconductor. The electrical properties of the structure were executed by the help of current-voltage and capacitance-voltage measurements. The photovoltaic properties of the structure were executed under a solar simulator with AM1.5 global filter between 40 and 100mW/cm(2) illumination conditions. It was also reported that the -amylase enzyme produced from Bacillus licheniformis had a 3.65eV band gap value obtained from optical method.Öğe The calculation of electronic properties of an Ag/chitosan/n-Si Schottky barrier diode(Elsevier Science Sa, 2007) Akkilic, Kemal; Uzun, Ilhan; Kilicoglu, TahsinIn this study, the film of chitosan by adding the solution of chitosan being a polymeric compound on the top of an n-Si substrate and then by evaporating solvent was formed. It was seen that the chitosan/n-Si contact demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current-voltage (I-V) curves studied at room temperature. Average barrier height and ideality factor values for this structure were determined as 0.94 eV and 1.81, respectively. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitosan/n-Si substrate in the energy range (E-c-0.785) to (E-c-0.522) eV have been determined from the I-V characteristics. The interface state density N-ss ranges from 5.39 x 10(12) cm(-2) eV(-1) in (E-c-0.785) eV to 1.52 x 10(13) cm(-2) eV(-1) in (E-c-0.522) ev. The interface state density has an exponential rise with bias from the midgap towards the bottom of the conduction band. (c) 2007 Elsevier B.V. All rights reserved.Öğe Diester Molecules for Organic-Based Electrical and Photoelectrical Devices(Springer, 2017) Topal, Giray; Tombak, Ahmet; Yigitalp, Esref; Batibay, Derya; Kilicoglu, Tahsin; Ocak, Yusuf SelimDiester derivatives of terephthalic acid molecules were synthesized according to the literature. Au/Diester derivatives/n-Si organic-inorganic (OI) heterojunction-type devices were fabricated, and the current-voltage (I-V) characteristics of the devices have been investigated at room temperature. I-V characteristics demonstrated that all diodes had excellent rectification properties. Primary diode parameters such as series resistance and barrier height were extracted by using semi-log I-V plots and Norde methods, and were compared. It was seen that there was a substantial agreement between results obtained from two methods. Calculated barrier height values were about the same with 0.02-eV differences that were attributed to the series resistance. Ideality factors, which show how the diode closes to ideal diodes, were also extracted from semi-log I-V plots. Thus, the modification of the Au/n-Si diode potential barrier was accomplished using diester derivatives as an interlayer. The I-V measurements were repeated to characterize the devices at 100 mW/cm(2) illumination intensity with the help of a solar simulator with an AM1.5G filter.Öğe Effect of an organic compound (Methyl Red) interfacial layer on the calculation of characteristic parameters of an Al/Methyl Red/p-Si sandwich Schottky barrier diode(Elsevier Science Sa, 2008) Kilicoglu, TahsinAn Al/Methyl Red/p-Si sandwich Schottky barrier diode (SBD) has been fabricated by adding a solution of the organic compound Methyl Red in chloroform onto a p-Si substrate, and then evaporating the solvent. Current-voltage (I-V) measurements of the Al/Methyl Red/p-Si sandwich SBD have been carried out at room temperature and in the dark. The Al/Methyl Red/p-Si sandwich SBD demonstrated rectifying behavior. Barrier height (BH) and ideality factor values of 0.855 eV and 1.19, respectively, for this device have been determined from the forward-bias I-V characteristics. The Al/Methyl Red/p-Si sandwich SBD showed non-ideal I-V behavior with the value of ideality factor greater than unity. The energy distribution of the interface state density determined from I-V characteristics increases exponentially with bias from 3.68 x 10(12) cm(-2) eV(-1) at (0.81-E-v) eV to 9.99 x 10(13) cm(-2) eV(-1) at (0.69-E-v) eV. (C) 2007 Elsevier B.V. All rights reserved.Öğe Electrical and optical properties of Cu2ZnSnS4 grown by a thermal co-evaporation method and its diode application(Elsevier Sci Ltd, 2014) Tombak, Ahmet; Ocak, Yusuf Selim; Genisel, Mustafa Fatih; Kilicoglu, TahsinCu2ZnSnS4 (CZTS) is low cost and constitutes non-toxic materials abundant in the earth crust. Environment friendly solar cell absorber layers were fabricated by a thermal co-evaporation technique. Elemental composition of the film was stated by energy dispersive spectroscopy (EDS). Some optical and electrical properties such as absorption of light, absorption coefficient, optical band gap charge carrier density, sheet resistance and mobility were extracted. Optical band gap was found to be as 144 eV, besides, charge carrier density, resistivity and mobility were found as 2.14 x 10(19) cm(-3), 8.41 x 10(-4) Omega cm and 3.45 x 10(2) cm(2) V-1 s(-1), respectively. In this study Ag/CZTS/n-Si Schottky diode was fabricated and basic diode parameters including barrier height, ideality factor, and series resistance were concluded using current-voltage and capacitance-voltage measurements. Barrier height and ideality factor values were found from the measurements as 0.81 eV and 4.76, respectively, for Ag/CZTS/n-Si contact. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Electrical and photoelectrical characterization of a TTF/p-InP organic–inorganic heterojunction(Microelectronic Engineering, 2014) Kilicoglu, Tahsin; Tombak, Ahmet; Ocak, Yusuf Selim; Aydemir, MuratTetrathiafulvalene (TTF) with C6H4S4 molecular formula was used in the fabrication of organic inorganic (OI) heterojunction. The Al/TTF/p-InP/Au-Zn structure was fabricated by forming a thin TTF organic semiconductor on p-InP inorganic semiconductor and evaporating of Al metal on the film. The characteristic parameters of the device were determined by using current-voltage (I-V) and capacitance voltage (C-V) measurements. Interface state density distribution was calculated from the I-V characteristics. The I-V characteristics of the device were also examined at 100 mW/cm(2) illumination intensity by the help of a solar simulator with AM1.5 global filter. (C) 2014 Elsevier B.V. All rights reserved.Öğe Electrical and photoelectrical properties of Ag/n-type Si metal/semiconductor contact with organic interlayer(Elsevier Science Sa, 2015) Ozerden, Enise; Ocak, Yusuf Selim; Tombak, Ahmet; Kilicoglu, Tahsin; Turut, AbdulmecitElectrical and photoelectrical features of Metal/Organic Interlayer/Inorganic Semiconductor (MIS) Schottky device were investigated by using current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. For this purpose, 9,10-dihydrobenzo[a]pyrene-7(8H)-one (9,10-H2BaP) thin film was used as organic interlayer between Ag metal and n-Si semiconductor. Firstly, optical properties of the organic thin film were determined from optical absorption spectrum, and its optical band gap was found to be 3.73 eV. Then, the electrical parameters of the Ag/9,10-H2BaP/n-Si diode such as ideality factor (n), barrier height (Phi(b(I-V))), diffusion potential (V-d), barrier height (Phi(b(C-V))) and carrier concentration (N-d) were calculated from I-V and C-V characteristics at room temperature. The Fb values obtained from both measurements were compared with each other. Besides, the effect of light on I-V measurements of the structure was examined at illumination intensities ranging from 40 to 100 mW/cm(2) with 20 mW/cm(2) intervals using a solar simulator with AM1.5 filter. Light sensitivity, open circuit voltage (V-OC) and short circuit current (I-SC) parameters of Ag/9,10-H2BaP/n-Si structure were calculated from under light measurements. (C) 2015 Elsevier B.V. All rights reserved.Öğe Electrical and photovoltaic properties of an organic-inorganic heterojunction based on a BODIPY dye(Elsevier, 2011) Kilicoglu, Tahsin; Ocak, Yusuf SelimAn organic-inorganic heterojunction based on a BODIPY dyes has been produced by forming dye thin film on n-Si. The electrical parameters of the structure have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The ideality factor, the barrier height and the series resistance values of the diode have been calculated as 2.43, 0.84 eV, and about 1.3 k Omega, respectively. The diode behaves as a non-ideal diode because of the series resistance and interface layer. The barrier height value obtained from I-V measurement has been compared with one from C-V measurement. Moreover, it has been seen that the diode is highly sensitive to the light and the reverse bias current increases about 1 x 10(4) times at -1 V under 100 mW/cm(2) and AM1.5 illumination condition. The short photocurrent density (J(sc)) and the open circuit voltage (V-oc), the fill factor (FF) and power conversion efficiency (eta) have been determined as 3.78 mA/cm(2), 327 mV, 0.28 and 0.48 %, respectively. (C) 2010 Elsevier B.V. All rights reserved.Öğe Fabrication and electrical properties of an organic-inorganic device based on Coumarin 30 dye(Elsevier Sci Ltd, 2014) Tombak, Ahmet; Ocak, Yusuf Selim; Asubay, Sezai; Kilicoglu, Tahsin; Ozkahraman, FatmaA Coumarin 30/p-Si organic-inorganic device was fabricated by forming a Coumarin 30 thin film on a p-Si semiconductor. The resulting structure had excellent rectifying properties. Electrical parameters of the structure were determined from current-voltage (I-V) measurements in the temperature range 300-380 K. While the barrier height (phi(b)) increased with increasing temperature, the ideality factor and series resistance of the diode decreased. I-V measurements of the structure were also performed under a solar simulator with AM1.5 filter and 100 mW/cm(2) illumination intensity. The structure had 59 mu A short-circuit current and 337 mV open-circuit voltage. Furthermore, capacitance-voltage (C-V) measurements of an Al/Coumarin 30/p-Si diode were carried out at various frequencies. The phi(b), value obtained by using C-V values was compared with that obtained by using I-V data. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Modification of electrical and optical properties of CuO thin films by Ni doping(Springer, 2016) Baturay, Silan; Tombak, Ahmet; Kaya, Derya; Ocak, Yusuf Selim; Tokus, Murat; Aydemir, Murat; Kilicoglu, TahsinUndoped and Ni-doped CuO thin films were deposited onto glass substrates using a spin-coating technique at different doping concentrations (undoped, 2, 4, 6, and 10 %). X-ray diffraction patterns for undoped and Ni-doped CuO thin films indicated that the films were polycrystalline, with preferential growth in the (002), (111), and (-311) directions. Atomic force microscopy images revealed that the surface morphologies of the films were not uniform. Scanning electron microscopy images confirmed the presence of agglomerated particles on the surfaces; the coverage increased with the doping level. A Hall effect system with a van der Pauw configuration was used to investigate the electrical properties of the CuO films. The free charge carrier concentration decreased and hole mobility increased with increasing Ni concentration, with the exception of the 10 % Ni-doped CuO sample. Ultraviolet-visible spectroscopy measurements of the film samples indicated an average transmittance of 30-40 % in the visible range. The optical band gap decreased slightly for low-level doping and increased from 2.03 to 2.22 eV for 10 % Ni incorporation. The electrical and optical properties of the CuO films were modified by Ni doping, i.e. the band gap decreased and the mobility increased almost linearly, with the exception of the 10 % Ni-doped sample. SEM images of a undoped b 2 % c 4 % d 6 %, and e 10 % Ni-doped CuO thin films. [GRAPHICS]Öğe Optical, Electrical, and Morphological Effects of Yttrium Doping of Cadmium Oxide Thin Films Grown by Ultrasonic Spray Pyrolysis(Springer, 2017) Tombak, Ahmet; Baturay, Silan; Kilicoglu, Tahsin; Ocak, Yusuf SelimCdO films doped with Y concentrations of 0%, 1%, 2%, and 3% were deposited onto soda lime glass using ultrasonic spray pyrolysis. The effect of the doping level on the structural, morphological, optical, and electrical properties of the films was characterized. X-ray diffraction analysis was used to establish that all of the samples were polycrystalline and to determine the structural parameters, i.e., lattice spacing (d), phases and associated (hkl) planes, grain size (D), and dislocation density (delta). The films possessed high conductivity and carrier concentration, showing n-type semiconducting behavior. The films were almost transparent over the range from 600 nm to 1100 nm. The energy bandgap was 2.43 eV, 2.53 eV, 2.68 eV, and 2.70 eV for Y doping of 0%, 1%, 2%, and 3%, respectively. The refractive index and extinction coefficient of the films over the range from 700 nm to 1100 nm were determined by spectroscopic ellipsometry. Atomic force microscopy revealed the effect of Y doping on the surface morphology of the CdO films.Öğe An organic-inorganic rectifying contact based on a ZnPc derivative(Elsevier Sci Ltd, 2014) Ozerden, Enise; Yildiz, Mustafa; Ocak, Yusuf Selim; Tombak, Ahmet; Kilicoglu, TahsinAn organic-inorganic rectifying contact was fabricated by forming a thin film of a Zinc Phthalocyanine (ZnPc) derivative, Zinc 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H, 31H-phthalocyanine (oc-ZnPc), on a p-Si wafer and evaporating Al on the structure. The current-voltage (I-V) and capacitance-voltage (C-V) measurements of Al/oc-ZnPc/p-Si structure were taken in dark at room temperature. The I-V measurements proved that the structure showed excellent rectification. Some basic diode parameters like ideality factor and barrier height were calculated from lnI-V plot. Ideality factor and barrier height values were found as 144 and 0.78 eV, respectively. The series resistance value of the structure was determined as 5.46 k Omega by means of Norde functions. The C-V measurements were taken for various frequencies and it was seen that the capacitance value decreased with increasing frequency. In addition I-V measurements of the Al/oc-ZaPc/p-Si/Al were repeated under light which had illumination intensity of 40-100 mW/cm(2). It was observed that reverse bias current of the diode increased with the light intensity. Therefore, the structure showed photodiode characteristics and it can be used for electrical and optoelectronic applications. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Solar cells fabricated by spray pyrolysis deposited Cu2CdSnS4 thin films(Pergamon-Elsevier Science Ltd, 2020) Tombak, Ahmet; Kilicoglu, Tahsin; Ocak, Yusuf SelimCu2ZnSnS4 (CZTS) occurs in nature and is the most likely alternative to Cu(In,Ga)Se-2 (CIGS) thin film solar cells, which started to spread increasingly all over the world. CZTS is a very suitable absorber layer material for thin film solar cells due to containing cheap material. It has a 1.5 eV band gap that is appropriate for theoretical Shockley-Queisser limit values, and the large absorption coefficient (10(4) cm(-1)). Substitution of different metals and usage of low cost and easy controlled deposition systems may present advantages. Cu2CdSnS4 (CCTS) is a semiconductor with a band gap of 1.37 eV, and it has a large absorption coefficient over 10(4) cm(-1) that makes it a possible photovoltaic material. Its structure is similar to CZTS. In this study, Cu2CdSnS4 thin films were deposited by ultrasonic spray method at various substrate temperatures as an alternative absorber layer. The structural features of the thin films were determined by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) surface morphology by Scanning Electron Microscopy (SEM) and optical band gaps by UV-VIS-NIR data. A CCTS-based solar cell with 1.14% power conversion efficiency was obtained using the most appropriate thin film according to optical and structural properties. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Substrate temperature effects on reactively sputtered Cr2O3/n-Si heterojunctions(Iop Publishing Ltd, 2016) Ocak, Yusuf Selim; Issa, Ali Ahmed; Genisel, Mustafa Fatih; Tombak, Ahmet; Kilicoglu, TahsinTo see the effects of substrate temperature on Cr2O3/n-Si heterojunctions, Cr2O3 thin films were formed on n-Si and glass substrates at 40, 150 and 250 degrees C by radio frequency (RF) reactive sputtering technique. High purity Cr was used as target and oxygen was used as reactive gas. Optical properties of Cr2O3/n-Si thin films were analyzed using UV-vis data. The band gaps of the films were compared. The electrical properties of Cr2O3/n-Si heterojunction were tested by their current voltage (I-V) measurements in dark. It was observed that the heterojunction which was fabricated by forming Cr2O3 thin film at 250 degrees C gave better rectification. The characteristic electrical parameters such as barrier height, ideality factor and series resistance were calculated by using its I-V data. The influence of light intensity on photovoltaic effect behavior of the device was also calculated, finally the barrier height value of the structure obtained from capacitance-voltage (C-V) data were compared with the one calculated from I-V measurements.Öğe Synthesis, characterization and catalytic behavior in the Suzuki reaction of Schiff base and its complexes and the optical properties of nickel complex used in the fabrication of a photodiode(Elsevier Science Sa, 2013) Pasa, Salih; Ocak, Yusuf Selim; Temel, Hamdi; Kilicoglu, TahsinSchiff base ligand N,N'-bis(2-hydroxy-1-naphtaldehydene)-1,4-bis(o-amino phenilthio)butane (L) derived from 2-hydroxy-1-naphthaldehyde and 1,4-bis(o-amino thiophenol)butane was synthesized and characterized by FTIR-ATR, H-1 NMR, MS, TGA/DTA, elemental analysis, UV-Vis Spectroscopy. The reactions of the ligand with different transition metal(11) salts under reflux system condition afforded a series of metal complexes such as Cu(II), Co(III), Ni(II), Pd(II). Palladium-catalyzed Suzuki cross-coupling reactions employing Schiff-base as ligand toward a various of substituted arylbromides and boronic acids were pursued. The conversions obtained and yields with different arylbromides were calculated and summarized. The transmission and absorbance spectra of the Ni(II) complex were taken by UV-Vis spectrophotometer, and direct and indirect band gap values were determined by optical method. A photodiode was fabricated by forming a thin film on n-Si wafer and evaporating Au contact onto the film. It was seen that the structure has a good rectification. The electrical properties of the diode were calculated using current voltage measurements. Furthermore, the effect of light on current voltage measurements of the structure was examined using a solar simulator with AM1.5 filter at various illumination intensities. (C) 2013 Elsevier B.V. All rights reserved.
