44 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 10 / 44
Öğe N-type InP Schottky diodes with organic thin layer: Electrical and interfacial properties(Journal of Vacuum Science & Technology B, 2010-03) Güllü, Ömer; Turut, AbdulmecitThe rectifying junction characteristics of methyl red (MR) organic film on n-type InP substrate have been studied. It has been observed that MR-based structure shows an excellent rectifying behavior and that the MR film increases the effective barrier height by influencing the space charge region of the n-type InP. The barrier height and ideality factor values for this structure have been obtained as 0.75 eV and 1.93 from the forward bias current-voltage characteristics, respectively. By using capacitance-voltage characteristics at 1 MHz, the barrier height and the carrier concentration values have been calculated as 0.93 eV and 5.13×1015 cm−3, respectively. The energy distributions of the interface states and their relaxation times have been determined from the forward bias capacitance-frequency and conductance-frequency characteristics. Moreover, it was seen that both the interface-state density and the relaxation time of the interface states decreased with bias voltage from experimental results.Öğe Temperature dependent electrical transport in Al/Poly(4-vinyl phenol)/ p -GaAs metal-oxide-semiconductor by sol-gel spin coating method(Hindawi, 2016-03-10) Özden, Şadan; Tozlu, Cem; Pakma, OsmanDeposition of poly(4-vinyl phenol) insulator layer is carried out by applying the spin coating technique onto p-type GaAs substrate so as to create Al/poly(4-vinyl phenol)/p-GaAs metal-oxide-semiconductor (MOS) structure. Temperature was set to 80-320 K while the current-voltage (I-V) characteristics of the structure were examined in the study. Ideality factor (n) and barrier height (φ b) values found in the experiment ranged from 3.13 and 0.616 eV (320 K) to 11.56 and 0.147 eV (80 K). Comparing the thermionic field emission theory and thermionic emission theory, the temperature dependent ideality factor behavior displayed that thermionic field emission theory is more valid than the latter. The calculated tunneling energy was 96 meV.Öğe Ag-doped HfO2 thin films via sol–gel dip coating method(Springer Nature, 2019-10-01) Pakma, Osman; Kaval, Şehmus; Kari̇per, İshak AfşinIn this study, undoped and Ag-doped HfO2 thin films were deposited on glass substrates by means of sol–gel dip coating method. These films were then thermally annealed at 500 °C for 1 h. The structural and optical properties of undoped and Ag-doped HfO2 thin films were characterized by X-ray diffraction, UV–Vis spectrometry and scanning electron microscope. The results of this analysis were compared and interpreted with the results obtained in literature by various methods of coating with HfO2. The X-ray diffraction peaks of the films paired with monoclinic HfO2 crystalline peaks. The refractive indices of the films decreased with doping Ag, at 500 nm wavelengths. The optical band gap values of Ag-doped HfO2 thin films increased with doping Ag. The porous structures were observed on the surface films, especially with 5% Ag doping.Öğe Wet chemical methods for producing mixing crystalline phase ZrO 2 thin film(Elsevier, 2016-07) Pakma, Osman; Özdemir, Cengiz; Kariper, İshak Afşin; Özaydın, Cihat; Güllü, ÖmerThe aim of the study is to develop a more economical and easier method for obtaining ZrO 2 thin films at lower temperature, unlike the ones mentioned in the literature. For this purpose, wet chemical synthesis methods have been tested and XRD, UV-VIS and SEM analysis of ZrO 2 thin films have been performed. At the end of the analysis, we identified the best method and it has been found that the features of the films produced with this method were better than the films produced by using different reagents, as well as the films reported in the literature. Especially it has been observed that the transmittance of the film produced with this method were higher and better than the films in the literature and the others. In addition, refractive index of the film produced with this method was observed to be lower. Moreover, by using the same method Al/ZrO 2 /p-Si structure has been obtained and it has been compared with Al/p-Si reference structure in terms of electrical parameters.Öğe Improvement of diode parameters in Al/n-Si schottky diodes with coronene interlayer using variation of the illumination intensity(Elsevier, 2017-12-15) Pakma, Osman; Çavdar, Şükrü; Koralay, Haluk; Tuğluoğlu, Nihat; Yüksel, Ömer FarukIn present work, Coronene thin films on Si wafer have been deposited by the spin coating method. It has been ultimately produced Al/Coronene/n-Si/In Schottky diode. Current–voltage (I-V) measurements have been used to determine the effect of illumination intensity in the Schottky diodes. The barrier height (ΦB) values increased as ideality factor (n) values decreased with a increase in illumination intensity. The ΦB values have been found to be 0.697 and 0.755 eV at dark and 100 mW/cm2, respectively. The n values have been found to be 2.81 and 2.07 at dark and 100 mW/cm2, respectively. Additionally, the series resistance (Rs) values from modified Norde method and interface state density (Nss) values using current-voltage measurements have been determined. The values of Rs have been found to be 1924 and 5094 Ω at dark and 100 mW/cm2, respectively. The values of Nss have been found to be 4.76 × 1012 and 3.15 × 1012 eV−1 cm−2 at dark and 100 mW/cm2, respectively. The diode parameters are improved by applying the variation of illumination intensity to the formed Schottky diodes.Öğe Radiation dose estimation and mass attenuation coefficients ofcement samples used in Turkey(Elsevier, 2009-12-16) Damla, Nevzat; Çevik, Uğur; Kobya, Ali İhsan; Çelik, Ahmet; Çelik, Necati; Grieken, R. VanDifferent cement samples commonly used in building construction in Turkey have been analyzed for natural radioactivity using gamma-ray spectrometry. The mean activity concentrations observed in the cement samples were 52, 40 and 324 Bq kg−1 for 226Ra, 232Th and 40K, respectively. The measured activity concentrations for these radionuclides were compared with the reported data of other countries and world average limits. The radiological hazard parameters such as radium equivalent activities (Raeq), gamma index (Iγ) and alpha index (Iα) indices as well as terrestrial absorbed dose and annual effective dose rate were calculated and compared with the international data. The Raeq values of cement are lower than the limit of 370 Bq kg−1, equivalent to a gamma dose of 1.5 mSv y−1. Moreover, the mass attenuation coefficients were determined experimentally and calculated theoretically using XCOM in some cement samples. Also, chemical compositions analyses of the cement samples were investigated.Öğe Morphological, structural and optical characteristics of graphene oxide layers and metal/interlayer/semiconductor photovoltaic diode application(National Institute of Research and Development for Optoelectronics, 2018) Güllü, Ömer; Çankaya, MuratThis work describes the optical, morphological and structural characterizations of graphene oxide (GO) layers grown by drop casting and annealing process. UV-vis optical measurement shows that the values of direct and indirect optical gap energy of the GO film are 3.89 eV and 3.21 eV, respectively. The graphene oxide (GO) layer has been placed in the metal/ interlayer /semiconductor (MIS) diodes (total 17 devices) on p-Si wafers. The graphene oxide diodes give a better barrier height enhancement as compared with the conventional diodes. The value of homogeneous barrier height for Al/GO/p-Si MIS junctions was extracted as 0.74 eV. The diodes were also investigated under 300 watt light illumination for photovoltaic applications. Additionally, interfacial properties of the MIS diode with GO interlayer were determined. It has been seen that the capacitance of the device changes as a function of gate voltage and signal frequency from the capacitance-frequency measurements. It has also been reported that the interfacial trap charges reduce the capacitance with increasing frequency values.Öğe Electrical analysis of organic dye based MIS Schottky contacts(Microelectronic Engineering, 2010-05-25) Güllü, Ömer; Turut, AbdulmecitIn this work, we prepared metal/interlayer/semiconductor (MIS) diodes by coating of an organic film onp-Si substrate. Metal(Al)/interlayer(Orange G@OG)/semiconductor(p-Si) MIS structure had a good recti-fying behavior. By using the forward-biasI–Vcharacteristics, the values of ideality factor (n) and barrierheight (BH) for the Al/OG/p-Si MIS diode were obtained as 1.73 and 0.77 eV, respectively. It was seen thatthe BH value of 0.77 eV calculated for the Al/OG/p-Si MIS diode was significantly larger than the value of0.50 eV of conventional Al/p-Si Schottky diodes. Modification of the potential barrier of Al/p-Si diode wasachieved by using thin interlayer of the OG organic material. This was attributed to the fact that the OGorganic interlayer increased the effective barrier height by influencing the space charge region of Si. Theinterface-state density of the MIS diode was found to vary from 2.79x1013to 5.80x1012eVx1cmx2.Öğe Electronic properties of the metal organic interlayer inorganic semiconductor sandwich device(Elsevier, 2010-03) Güllü, Ömer; Turut, Abdulmecit; Kılıçoğlu, TahsinIn this study, we prepared a Metal(Al)/Organic Interlayer(Congo Red=CR)/Inorganic Semiconductor (p-Si) (MIS) Schottky device formed by coating of an organic film on p-Si semiconductor wafer. The Al/CR/p-Si MIS device had a good rectifying behavior. By using the forward bias I–V characteristics, the values of ideality factor (n) and barrier height (Φb) for the Al/CR/p-Si MIS device were obtained as 1.68 and 0.77 eV, respectively. It was seen that the Φb value of 0.77 eV calculated for the Al/CR/p-Si MIS device was significantly higher than value of 0.50 eV of the conventional Al/p-Si Schottky diodes. Modification of the interfacial potential barrier of the Al/p-Si diode was achieved by using a thin interlayer of the CR organic material. This was attributed to the fact that the CR organic interlayer increased the effective barrier height by influencing the space charge region of Si. The interface-state density of the MIS diode was found to vary from 1.24×1013 to 2.44×1012 eV−1 cm−2.Öğe Photoelectric and photocapacitance characteristics of Au/pyrene/N-Si MIS structures(Journal of Non-Oxide Glasses, 2017-04-01) Güllü, Ömer; Pakma, Osman; Özaydın, Cihat; Arsel, İsmail; Turmuş, MesutThis paper presents in-depth analysis of the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of identically prepared Au/Pyrene(C16H10)/n-Si hybrid organic-oninorganic semiconductor photovoltaic cells (total 43 diodes). The barrier heights, ideality factors and reverse bias saturation currents of all devices were extracted from the electrical characteristics. The mean barrier height, mean ideality factor and mean saturation current from I-V measurements were calculated as 0.79 ± 0.01 eV, 1.40 ± 0.08 and (1.01 ± 0.46)x10-8 A, respectively. Also, the photoelectric (I-V) and photocapacitance (C-V and conductance (G)-voltage (V)) characteristics of the Au/Pyrene/n-Si device under 100 mW/cm2 light illumination were investigated. It has been seen that the light illumination increases strongly the current, capacitance and conductance values of the device due to electron-hole charge pair generation. The C-V and G-V characteristics under illumination have shown a non-monotonic dependence of capacitance on frequency giving rise to a peak. This is attributed to the existence of electrically active traps. The open circuit voltage and short circuit current of the Au/Pyrene/n-Si device were extracted as 80 mV and 30 µA, respectively.
