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Öğe Change of mineral element content in the common shrubs of mediterranean zone. i. macronutrients(Lithuanian Research Centre for Agriculture and Forestry; Vytautas Magnus University, 2011) Gökkuş, A.; Özaslan Parlak, A.; Parlak, M.Shrubs are characteristic of Mediterranean zone and are a significant feed source for goats. However, nutrientcontents of shrubs vary significantly with climate, soil and especially with plant growth. There are a few studieson annual variations in mineral contents of shrubs in Marmara Region. Therefore, in this study, seasonal variationof macronutrients (N, P, K, Ca, Mg, S) of kermes oak (Quercus coccifera L.), mock privet (Phillyrea latifolia L.),prickly juniper (Juniperus oxycedrus L.), gall oak (Quercus infectoria Oliv.), Christ's-thorn (Paliurus spina-christiMiller), pink rockrose (Cistus creticus L.), thyme (Thymus longicaulis C. Presl.) and prickly burnet (Sarcopoteriumspinosum (L.) Spach) were investigated for 14 months (October 2006-November 2007). Variation of macronutrientsthroughout the year was found to be significant for all shrubs. The concentrations of N, P, K, and S in the shrubsreached the highest levels during the April-May months. However, Ca significantly decreased in April. Variationin Mg varied with shrub species. While the amount of N was able to meet the demands of goats during spring forall shrubs except for Paliurus spina-christi and Quercus infectoria, they were not able to meet the demands inother seasons. While Paliurus spina-christi had sufficient N every season, Quercus infectoria had also sufficientN during each season except for winter. P, K, and Ca were mostly observed at sufficient amounts for goats. WhileJuniperus oxycedrus had insufficient Mg in every season and mock privet in summer and autumn, Mg deficiencywas not observed in other shrubs. Amounts of S were generally insufficient for the needs of goats.Öğe Characterization of Co-evaporated Cu-Ag-In-Se Thin Films(Springer, 2014) Gullu, H. H.; Coskun, E.; Parlak, M.In this study, annealing effect on the structural, electrical, and optical characteristics of the quaternary Cu-Ag-In-Se (CAIS) thin films was investigated. These samples were deposited by co-evaporation of the Cu, Ag, In2Se3, and Se sources at the substrate temperature of 300 degrees C. The structural properties of the thin films were analyzed by means of X-ray diffraction, and the results indicated that all of the films were in the polycrystalline structure with the preferred orientation along (112) direction. From the optical measurements, the band gap values were found to vary between 1.38 and 1.45 eV with annealing processes. The temperature-dependent electrical conductivity of the samples was measured in the temperature range of 90-400 K. The films gained degenerate behavior with increasing annealing temperature. The carrier conduction mechanism was determined at high- and low-temperature regions by comparing thermionic emission and hopping parameters. Photoconductivity of the as-grown film showed that there was an increase in conductivity with increasing illumination intensity. From this measurement, the variation of photocurrent as a function of illumination intensity was determined.Öğe Device application of AgGa0.5In0.5Se2 thin films deposited by thermal sequential stacked layer method(Iop Publishing Ltd, 2014) Coskun, E.; Gullu, H. H.; Parlak, M.An In/n-AgGa0.5In0.5Se2/p-Si/Al heterostructure was produced by thermal sequential stacked layer deposition method and the device characteristics were investigated. The compositional analysis showed that the depositions of the intended stoichiometric composition of AgGa0.5In0.5Se2 structure were obtainable by controlling and providing the necessary deposition conditions during the deposition processes. By means of the room temperature Hall effect and transmission measurements, the carrier concentration and optical band gap values were determined as 9 x 10(15) cm(-3) and 1.65 eV, respectively. In addition, temperature- dependent current-voltage (I-V) and the room temperature capacitance-voltage (C-V) measurements of this heterostructure were carried out. The rectification factor was obtained as about 10(4) at 1.20V for all sample temperatures. Depending on the change in the temperature, the series and shunt resistances were calculated as 10(1) and 10(6) Omega, respectively. The studies on the current transport mechanisms showed that there were two different mechanisms at two different voltage regions: tunneling enhanced recombination mechanism in the voltage range of 0.08 and 0.30V and the space charge limited current mechanism in the voltage range of 0.30 and 0.60 V. The barrier height, built-in potential and interface states density of the deposited heterostructure were also calculated and discussed.Öğe Device behavior of an In/p-Ag(Ga,In)Te2/n-Si/Ag heterojunction diode(Elsevier Sci Ltd, 2015) Coskun, E.; Gullu, H. H.; Candan, I.; Bayrakli, O.; Parlak, M.; Ercelebi, C.In this work, p-(Ag-Ga-In-Te) polycrystalline thin films were deposited on soda-lime glass and n-type Si substrates by e-beam evaporation of AgGa0.5In0.5Te2 crystalline powder and the thermal evaporation of Ag powder, sequentially in the same chamber. The carrier concentration and mobility of the Ag-Ga-In-Te (AGIT) film were determined as 5.82 x 10(15) cm(-3) and 13.81 cm(2)/(V s) as a result of Hall Effect measurement. The optical analysis indicated that the band gap values of the samples were around 1.58 eV. The structural analysis was carried out by means of X-ray diffraction. Current-Voltage (I-V) measurements depending on the sample temperature were performed to investigate the device characteristics and the dominant conduction mechanism in an In/p-AGIT/n-Si/Ag structure. The series and shunt resistances were calculated by the help of parasitic resistance analysis as 5.73 and 1.57 x 10(4) Omega cm(2), respectively at room temperature. The ideality factors and barrier heights were evaluated as a function of sample temperature. In the low bias region, the thermionic emission together with the generation-recombination mechanism was investigated as the dominant transport mechanism; however, in the high bias region, space charge limited current was analyzed as the other effective mechanism in the carrier conduction. The built-in potential of the device was also determined by the help of capacitance-voltage measurements. (C) 2015 Elsevier Ltd. All rights reserved.Öğe Effects of Si nanowire on the device properties of n-ZnSe/p-Si heterostructure(Springer, 2019) Coskun, E.; Gullu, H. H.; Colakoglu, T.; Emir, C.; Bozdogan, E.; Parlak, M.The semiconductor nanowire (NW) technology has raised attention owing to its one-dimensional geometry as a solution for lattice mismatch in the fabricated heterostructures. Although, SiNWs have been investigated for various device technologies, there is no published work on the p-n junction formed by deposition of ZnSe thin film on these NW structures, in which this film layer has significant optical and electrical properties in optoelectronics applications. The aim of this study is determining the device properties of n-ZnSe/SiNW heterojunction and obtaining the enhancement in the device application of the NW structure on Si surface with comparing to planar surface. SiNW was produced by metal assisted etching method as a cost-efficient process, and the ZnSe film was deposited on SiNW and planar Si substrates by thermal evaporation of elemental sources. The optical band gap of the deposited ZnSe film was determined as 2.7eV which is in a good agreement with literature. The ideality factor and series resistance values of the ZnSe/SiNW and ZnSe/Si heterojunctions were calculated as 3.12, 461 , and 4.52, 7.26x103, respectively. As a result of utilizing SiNW structure, a spectacular improvement in terms of the physical parameters related to device properties was achieved.Öğe FABRICATION AND CHARACTERIZATION OF TiO2 THIN FILM FOR DEVICE APPLICATIONS(World Scientific Publ Co Pte Ltd, 2019) Hosseini, A.; Gullu, H. H.; Coskun, E.; Parlak, M.; Ercelebi, C.Titanium oxide (TiO2) film was deposited by rectification factor (RF) magnetron sputtering technique on glass substrates and p-Si (111) wafers to fabricate n-TiO2/p-Si heterojunction devices for the investigation of material and device properties, respectively. The structural, surface morphology, optical and electrical properties of TiO(2 )film were characterized by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV-visual (UV-Vis) spectral and dark current-voltage (I-V) measurement analyses. The deposited film layer was found to be homogeneous structure with crack-free surface. The bandgap value of TiO2 film was determined as 3.6 eV and transmission was around 65-85% in the spectral range of 320-1100 nm. The conductivity type of the deposited film was determined as n-type by hot probe method. These values make TiO2 film a suitable candidate as the n-type window layer in possible diode applications. TiO2 film was also deposited on p-Si (111) wafer to obtain Al/n-TiO2/p-Si/Al heterojunction device structure. The dark I-V characteristic was studied to determine the possible conduction mechanisms and diode parameters.Öğe Improvement of electrical characteristics of SnSe/Si heterostructure by integration of Si nanowires(Elsevier B.V., 2021) Coşkun, Emre; Güllü, H. H.; Emir, C.; Parlak, M.In this study, the effects of the nanowire geometry on Si wafer substrate were investigated for the SnSe/Si-nanowire heterojunction device and the obtained results were compared with the one fabricated on planar Si surface. Nanowires on Si surface were produced by metal-assisted etching method and the SnSe film layer was deposited by thermal evaporation technique. On both Si and glass surfaces, deposited film shows polycrystalline and single SnSe phase. From optical transmission measurements, optical band gap of this film was determined as 1.36 eV in a good agreement with the literature. All SnSe/Si heterostructures were found in a p-n diode behavior and the ideality factor and series resistance values were calculated as 2.40, 547 Ω, and 3.71, 1.57 × 103 Ω, for SnSe/Si-nanowire and SnSe/Si heterojunctions, respectively. As a result, an improvement in device characteristics concerning the planar Si structure was found by utilizing Si nanowire structure.Öğe Investigation of optical parameters of Ag-In-Se thin films deposited by e-beam technique(Elsevier Science Bv, 2008) Colakoglu, T.; Parlak, M.; Ozder, S.The optical properties of the Ag-In-Se (AlS) thin films deposited by e-beam technique were investigated by means of the optical transmittance measurements. The optical absorption coefficients of the films were found to vary from 10(3) to 10(5) cm(-1) over the wavelength range of 300-1100 nm. The real and imaginary parts of the refractive index and dielectric constant for the as-grown and annealed films in between 100 and 400 degrees C were evaluated by means of both envelope method (EM) and continuous wavelet transform (CWT) method and the results were in quite good agreement with each other. The refractive index, n, dispersion over the measured wavelength range was explained by applying single-oscillator model (SOM) and the related parameters were calculated. The optical absorption process for the AIS thin films was characterized by three direct transitions from three closely spaced valence bands to a single conduction band due to the splitting of the valence band under the influence of the tetragonal crystalline field and spin-orbit interaction. The direct optical band gap energy decreases as the annealing temperature increases because of the increase in the width of band tail states near valence-band edge caused by the Se segregation. The two distinct parameters of the quasicubic model; crystal-field splitting Delta(CF), and spin-orbit splitting, Delta(SO), were calculated for as-grown and annealed AlS thin films. (C) 2008 Elsevier B.V. All rights reserved.Öğe Investigation of optical parameters of thermally evaporated ZnSe thin films(Wiley-V C H Verlag Gmbh, 2015) Gullu, H. H.; Coskun, E.; Parlak, M.In this work, zinc selenide (ZnSe) thin films were deposited by thermal evaporation method using pure elemental (Zn and Se) sources. The physical properties of the films have been investigated in terms of the structural and optical characterizations depending on the post-annealing process under nitrogen atmosphere in the temperature between 300 and 500 degrees C for 30 min. The structural and compositional analyses were carried out by means of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The compositional analysis indicated that the deposited films were nearly stoichiometric whereas there was a decrease in Se and increase in the Zn contents. This implies the segregation and/or re-evaporation of Se atoms from the thin film structure. The optical characteristics were studied by using the room temperature transmission measurements. The analysis of transmission values showed that the band gap values changed in between 2.38 and 2.62 eV depending on the annealing temperatures. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimÖğe Investigation of structural and optical parameters of Cu-Ag-In-Se thin films deposited by thermal evaporation method(Elsevier Gmbh, 2015) Gullu, H. H.; Candan, I.; Coskun, E.; Parlak, M.Annealing effect on the structural and optical properties of the quaternary Cu-Ag-In-Se thin film deposited by the thermal evaporation has been investigated. The evaporation source was prepared by using vertical Bridgman-Stockbarger crystal growth system. Structural analysis indicated that annealing the films following to the deposition resulted in the changes from amorphous to polycrystalline phase with the preferred orientation along (1 1 2) direction. In order to determine the optical properties of the thin films as a function of annealing temperature, the transmission measurements were carried out in between 300 and 2000 nm. The optical band gap values were lying in between 1.29 and 1.50 eV upon annealing the thin films in the temperature range of 300-500 degrees C. The refractive indices of the samples were in the range of 2.7-3.8 depending on the wavelength region and annealing temperature by applying the Envelope Method. The other optical constants of the samples were also calculated using Cauchy Method and Single Oscillator Model. (C) 2015 Elsevier GmbH. All rights reserved.Öğe Investigations of thermal annealing role on the optical properties of Zn-In-Se thin films(Elsevier Gmbh, 2017) Gullu, H. H.; Coskun, E.; Parlak, M.Zn-In-Se (ZIS) thin films were prepared by sequential evaporation of its elemental sources on the glass substrates. The effect of thermal annealing under nitrogen environment on the optical properties of the films was discussed. In addition to the comparative study of three different annealing temperatures, the results were analyzed by relating with their structural and compositional characteristics. The optical analyses were based on the observed interference fringes on their transmission spectra of the films. The refractive indices were calculated by means of envelope method (EM) and the continuity of the refractive indices was evaluated by three-term Cauchy fitting process. From the results of the refractive index calculations, the real and imaginary part of the dielectric constant were determined. The optical absorption coefficients of the films were found in the range of 10(3)-10(4) cm(-1) over the visible and near-infrared region and by using these values, the extinction coefficients were calculated. Moreover, the band gap values were calculated from the corresponding Tauc plots, and the refractive index dispersion over the measured wavelength range was investigated with single-oscillator model (SOM) and the related parameters were obtained. (C) 2017 Elsevier GmbH. All rights reserved.Öğe Soil losses due to potato harvesting: a case study in western Turkey(Wiley, 2015) Parlak, M.; Blanco-Canqui, H.Harvesting of potato (Solanum tuberosum L.) may cause soil losses, but the magnitude of such losses has not been widely documented. We quantified the amount of soil lost with the mechanical harvesting of potatoes in 39 fields in western Turkey in 2013. The amount of soil lost was 1.81Mg/ha/harvest and increased with increased gravimetric water content and plant density. The cost to replace nutrients lost with soil was about US$3 per hectare. Overall, soil loss due to potato harvesting is an important component of total erosion in the study region.Öğe Structural and optical properties of Zn-In-Te thin films deposited by thermal evaporation technique(Elsevier Science Sa, 2013) Gullu, H. H.; Bayrakli, O.; Candan, I.; Coskun, E.; Parlak, M.Annealing effects on structural and optical properties of the thermally evaporated Zn-In-Te(ZIT) thin films have been investigated. The structural and the compositional analyses were carried out by means of X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDXA). The as-grown and annealed ZIT films had polycrystalline structure and the preferred orientation changed from (220) to (112) direction with increasing annealing temperature. The optical properties and constants were determined by transmittance measurements in the wavelength range of 200-2000 nm. The effect of annealing on the optical parameters was determined by using Single Oscillator Model (SOM), Envelope Model (EM) and Cauchy Method. The absorbance studies revealed that the films had three distinct transitions in the high absorption region because of the tetragonal distortion, and that was used to evaluate the splitting energies of crystal-field and spin-orbit splitting. The fundamental optical band gap values were found to be lying in the range of 1.51 and 1.72 eV and the notable change of the band gaps due to annealing temperatures was observed. Finally, the Urbach energies were calculated and it was observed that the band tail energies were increasing with increasing annealing temperature. (C) 2013 Elsevier B. V. All rights reserved.Öğe Study on the Structural and Electrical Properties of Sequentially Deposited Ag-Ga-In-Te Thin Films(Springer/Plenum Publishers, 2015) Coskun, E.; Gullu, H. H.; Parlak, M.; Ercelebi, C.The structural properties and electrical conduction mechanisms of Ag-Ga-In-Te thin films deposited by a combination of e-beam and thermal evaporation methods were studied for various annealing temperatures. Structural analysis showed the existence of InTe and InTe binary phases at the early stage of crystallization and monophase of AgGaInTe with the main orientation along (112) direction following the post-annealing at 400 C. The effects of the structural changes on electrical properties and temperature dependence of the electrical conductivity of Ag-Ga-In-Te thin films were studied in the temperature range of 90-400 K. The analysis of electrical conductivity revealed the Efros-Shklovskii variable range hopping (VRH) mechanism in between 90 and 210 K and Mott VRH mechanisms for the temperature range of 250-400 K for all deposited films. The VRH parameters including average hopping distance, average hopping energy and characteristic temperature coefficient for Efros-Shklovskii and Mott VRH mechanisms were determined and discussed in detail.
