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Öğe Design of PV energy system in Batman Turkey(AIP Conf.Proc., 2017) Pakma, Nilay; Pakma, Osman; Güllü, ÖmerÖğe Fabrication and electrical characterization of ZnO SiO2 p Si structure with outsized diode factor(European Union, 2010) Kavasoğlu, Neşe; Kavasoğlu, Abdülkadir Sertap; Pakma, Osman; Kabakçı, Murat; Birgi, Özcan; Oktik, ŞenerÖğe Frequency dependent interface state properties of a schottky device based on coronene deposited on n-type silicon by spin coating technique(Ulusal Fotovoltaik Teknoloji Platformu, 2016) Yüksel, Ömer Faruk; Pakma, Osman; Tuğluoğlu, NihatÖğe Some electrical parameters of the Sn/p-Si diode under γ-irradiation(Çukurova Üniversitesi, 2017) Pakma, Osman; Güllü, ÖmerThe radiation response of metal-semiconductor (MS) contacts has been found to alter significantly when the structures are exposed to pre-irradiation processes at determined doses. Radiation doses greater than a kilogray exposure may cause strong changes on the electrical characteristics of MS structures. It has been also shown that the particle or gamma irradiations induce defects in the band gap which affects the free carrier concentration and leads to an increase and decrease of barrier height in p-type and n-type semiconductors, respectively. The knowledge of the influence of radiation damage on the Schottky barrier diodes (SBDs) performance is a fundamental field of research, having technological relevance for many applications in the semiconductor electronic devices. Hence, it is very much essential to evaluate the effect of irradiation and identify the degradation mechanism to understand the failure mechanisms. In this work, we have investigated the electrical parameters of the Sn/p-Si Schottky barrier diodes by using I-V and C-V characteristics under γ-irradiation at room temperature. The basic diode parameters such as ideality factor, barrier height, series resistance and reverse saturation current were extracted from electrical measurements as a function of the irradiation dose. The results indicated that γ-irradiation induced an increase in the effective Schottky barrier height extracted from both I-V and C-V measurements. Also, it was seen that ideality factor increased with the increasing γ-irradiation doses. We have also observed that the reverse bias current of the Sn/Si contact exceedingly decreased with increasing irradiation dose with low energy (60 keV). The basic results as related to the gamma irradiation have been indicated that this device may have applications as radiation sensors in order to detect the low energy gamma radiation.Öğe Characterization of Au N Inp photovoltaic structure with organic thin film(Uppsala University, 2012) Güllü, Ömer; Özerden, Enise; Rüzgar, Şerif; Asubay, Sezai; Pakma, Osman; Kılıçoğlu, Tahsin; Türüt, AbdulmecitÖğe The effects of high-energy electron irradiation on the electrical characteristics of a lead/rhodamine-101/p-Si diode(Çukurova Üniversitesi, 2017) Güllü, Ömer; Pakma, OsmanHigh-energy radiation penetrates the metal-semiconductor (MS) interface and causes damage deep below the interface. Low-energy radiation causes severe lattice damage in the form of vacancies, interstitials and defect complexes at the near interface of the device. The one kind of the radiation is electron beam which is accelerated. Mills was the first to recognize that electrons with energy of 1 MeV would possess enough energy to displace an atom from its lattice position. This observation has led to the increased use of electron accelerators in radiation damage studies. This use has been motivated by two important facts. First, electron bombardment experiments permit the determination of the energy required to remove an atom from its initial position. This is done by increasing the energy of the electrons until an observable change in a radiation-sensitive property is seen. The second important basis for the use electrons lie in the fact that as long as the energy of the electrons is close to the displacement threshold, it is presumed, that only single Frenkel pairs are formed. Thus, many radiation-induced phenomena can be analyzed in terms of a single vacancy and/or interstitial atom, and one avoids the complication attendant upon the generation of complex damage regions presumed to occur in heavy-charged particle irradiation. In the present paper, a lead/rhodamine-101(Rh101)/p-Si metal/organic interlayer/ semi-conductor diode was fabricated and the effect of 6 MeV-electron irradiation on the electrical characteristics of the diode structure was investigated. It was seen that after electron irradiation the barrier height values, the series resistance values and ideality factors increased. Furthermore, it was seen that the capacitance values increased after electron irradiation. This was attributed to the change in dielectric constant at the interface and/or to decrease in the net ionized dopant concentration and the interface states. The degradation of the diode properties may be due to the introduction of electron irradiationinduced interfacial defects via displacement damage.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 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 I V and C V F characteristics of aniline green N type silicon diode(İstanbul University, 2015) Özkan, Samet; Güllü, Ömer; Arsel, İsmail; Özaydın, Cihat; Pakma, Osman; Turut, AbdülmecitWe have studied the I-V, C-V and C-f characteristics of the Aniline Green (AG)/n-type Si structure. In organic/inorganic semiconductor contact applications, in order to keep the technological difficulties and unknowns to a minimum, silicon is generally chosen as the substrate semiconducting material. In this structure, deposition of organic materials on the inorganic semiconductor can generate large number of interface states at the semiconductor surface that strongly influence the electrical properties of the AG/n-Si structure. The values of the ideality factor, series resistance and barrier height obtained from two methods were compared, and it was seen that there was an agreement with each other. The downward concave curvature of the forward bias current-voltage characteristics at sufficiently large voltages is caused by the presence of the effect of series resistance. Thus, the concavity of the forward bias current-voltage characteristics increases with the increasing series resistance value. The high resistance values have given the high ideality factors. Also, the higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the nSi that can follow the ac signal.
