Yazar "Polat, I." seçeneğine göre listele
Listeleniyor 1 - 16 / 16
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A research on growth and characterization of CdS:Eu thin films(Springer Heidelberg, 2019) Yilmaz, S.; Polat, I.; Tomakin, M.; Bacaksiz, E.Chemical spray pyrolysis-grown CdS thin films including various quantities of Eu atoms (from 0 to 10at.%) were synthesized on glass slides. The detailed physical properties of the produced CdS and CdS:Eu thin films were explored. Structural analysis showed that Eu-doping enhanced the crystal quality of CdS thin films until 10at.% Eu-doping and further Eu-doping treatment led to a distortion in the CdS structure. In addition, the crystallite sizes of CdS thin films dropped from 36.2 to 32.4nm as Eu-doping level increased to 10at.%. Morphological data showed that increasing Eu-doping remarkably varied the surface morphology of CdS thin films forming smaller grains. Chemical content examinations approved the presence of Eu atoms in CdS structure. From the optical measurements, it was obtained that more transparent CdS thin films with a maximum transmittance of 68% at 820nm were created after 10at.% Eu-doping and bandgap values of samples reduced from 2.58 to 2.47eV with rising of Eu-doping from 0 to 10at.%. Room temperature photoluminescence data demonstrated the formation of two essential peaks for all the samples, which are in turn related to green and yellow bands. Electrical investigation pointed out that Eu-doping enhanced the carrier density of CdS thin films from 4.38 x 10(13) cm(-3) to 2.46 x 10(14) cm(-3) and dropped the resistivity of CdS samples from 2.59 x 10(4) cm to 5.85 x 10(3) cm until 6at.% and further increment of Eu-doping paved the way to get worse electrical data. Thus, it can be brought a conclusion that Eu-doping not only improved the optical properties of CdS thin films, but also restored the electrical properties, which are able to use in the opto-electronic devices.Öğe An evaluation of structural, optical and electrical characteristics of Ag/ZnO rods/SnO2/In-Ga Schottky diode(Springer, 2018) Kucukomeroglu, T.; Yilmaz, S.; Polat, I.; Bacaksiz, E.ZnO rods were successfully deposited on ZnO seeded SnO2 coated glass substrates by a spray pyrolysis route. It was seen that the grown ZnO sample had a wurtzite structure with a well-defined hexagons of similar to 1-3 A mu m in diameter. Photoluminescence results measured at 300 K indicated that ZnO rods had a ultra-violet peak located at 383 nm without a deep level band emission. ZnO rods were subsequently used to realize a Ag/ZnO rods/SnO2/In-Ga Schottky diode which displayed rectifying current-voltage (I-V) characteristic with a turn on voltage of 1.2 V at 300 K. Electrical parameters of the Ag/ZnO rods/SnO2/In-Ga Schottky diode were further examined by (I-V) characteristics at the temperature range of 125-300 K with a step of 25 K. Using thermionic emission theory (TET), it was found that the ideality factor reduced with the increase of temperature whereas the zero bias barrier height increased with the increment of the temperature. Using ln(I (0) )/T (2) versus q/nkT plot, Richardson constant (A*) and zero bias barrier height (I broken vertical bar (B0)) was obtained as 3.27 x 10(-5) A m(-2) K-2 and 0.32 eV, respectively. After applying TET with the assumption of Gaussian distribution, a mean barrier height and the modified Richardson constant (A**) were determined to be 0.88 eV and 2.75 x 10(5) A m(-2) K-2.Öğe CdSe thin films-based photodetector doped with Cu, In and Ga atoms: a comparative work(Springer Heidelberg, 2023) Yilmaz, S.; Polat, I.; Tomakin, M.; Kucukomeroglu, T.; Bacaksiz, E.The present work demonstrates a comparison of performance of Cu, In and Ga-doped CdSe thin films-based photodetectors. Structural, morphological, optical and electrical investigation of Cu, In and Ga-doped CdSe thin films prepared by close space sublimation on glass slides is also achieved. It is obtained that Cu, In and Ga-doped CdSe thin films have a good crystal quality with a hexagonal structure in the preferred orientation along (002) plane. Morphological examination shows that Cu-doped CdSe thin films grow in the porous microstructure while In and Ga-doped CdSe films possess compact and uniform morphology without any voids. Transparency of In and Ga-doped CdSe films are higher than that of Cu-doped CdSe throughout the entire spectrum. Band gap values of all the samples are determined to be almost 1.72 eV. Photoluminescence data indicate that Ga-doped CdSe thin films display a deep level band at the lowest peak intensity, which is the indication of less defected structure. All the samples exhibit n-type conductivity. Additionally, the maximum carrier density and the minimum resistivity are reached for In-doped CdSe thin films as 1.75 x 10(16) cm(-3) and 6.12 & omega; cm, respectively. Rise time of 28 ms and fall time of 25 ms are obtained for Cu-doped CdSe thin films-based photodetector, which are the fastest photoresponse within all the devices. Furthermore, Cu-doped CdSe thin films-based device has a responsivity of 1.20 x 10(-2) A/W and a detectivity of 1.20 x 10(9) Jones that makes Cu-doped CdSe thin films-based device as a strong candidate for high sensitive photodetector applications.Öğe Determination of optimum Er-doping level to get high transparent and low resistive Cd1-xErxS thin films(Springer, 2019) Yilmaz, S.; Polat, I.; Tomakin, M.; Bacaksiz, E.Cd1-xErxS (x=0, 0.02, 0.04, 0.06, 0.08 and 0.10) thin films were produced by a chemical route on glass slides. The structural, morphological, optical and electrical properties of the grown samples were studied to obtain the optimum Er-doping level. Structural properties indicated that specimens had a hexagonal structure. Morphological analysis showed that the grain size of pristine CdS thin films remarkably reduced with rising Er-doping. The presence of Er atoms in CdS host structure was proved by energy dispersive of X-ray spectroscopy (EDS). The transparency of CdS thin films substantially improved after 10at.% Er-doping and a gradual decrease was acquired in the band gaps of the CdS samples with the increase of Er-doping. Photoluminescence data approved the existence of two main peaks corresponding to the green and yellow regions. Electrical properties of pristine CdS thin films were enhanced by Er-doping and the best electrical conclusions were obtained for Cd0.94Er0.06S thin films. Thus, it can be brought to an end that Er-doping enhanced both optical and electrical properties of pristine CdS thin films, which are of vital importance in optoelectronic applications.Öğe Enhancement in the optical and electrical properties of CdS thin films through Ga and K co-doping(Elsevier Sci Ltd, 2017) Yilmaz, S.; Toreli, S. B.; Polat, I.; Olgar, M. A.; Tomakin, M.; Bacaksiz, E.In the presented work, Ga-doped CdS and (Ga-K)-co-doped CdS thin films are grown on glass substrates at a temperature of 400 degrees C through spray pyrolysis. Influence of K-doping on structural, morphological, optical and electrical characteristics of CdS:Ga thin films are examined. K level is changed from 1 at% to 5 at% for CdS:Ga samples just as Ga concentration is fixed 2 at% for all CdS thin films. It is observed from the X-ray diffraction data that all the samples exhibit hexagonal structure and an increase level of K in Ga-doped CdS samples causes a degradation in the crystal quality. Energy-dispersive X-ray spectroscopy measurements illustrate that the best stoichiometric film is acquired when K content is 2 at% in Ga-doped CdS films. Optical transmission curves demonstrate that CdS:Ga thin films exhibit the best optical transparency in the visible range for 4 at% K content compared to other specimens. A widening in the optical bandgap is unveiled after K-dopings. It is obtained that maximum band gap value is found as 2.45 eV for 3 at%, 4 at% and 5 at%. K -dopings while Ga-doped CdS thin films display the band gap value of 2.43 eV. From photoluminescence measurements, the most intensified peak is observed in the deep level emission after incorporation of the 4 at% K atoms. As for electrical characterization results, the resistivity reduces and the carrier density improves with the increase of K concentration from 1 at% to 4 at%. Based on all the data, it can be deduced that 4 at% K-doped CdS:Ga thin films show the best optical and electrical behavior, which can be utilized for solar cell devices.Öğe Fabrication of CdS nanospheres-based hybrid solar cells having increased efficiency(Springer Heidelberg, 2022) Yilmaz, S.; Unverdi, A.; Tomakin, M.; Polat, I.; Bacaksiz, E.The impact of surface modification through diverse dyes (Eosin-Y, D205, N719 and N3) on structural, morphological, optical, and electrical properties of CdS/P3HT hybrid solar cells is studied. X-ray diffraction (XRD) pattern shows that CdS nanospheres have a hexagonal structure with a preferential orientation of (002) with respect to indium tin oxide (ITO) coated glass slide. Scanning electron microscopy (SEM) results indicate that compact and dense spherical morphologies of CdS occurred, and the P3HT layer also consisted of small spherical grains. The bandgap of CdS is found to be 2.52 eV according to Tauc's plot analysis. Absorption spectra demonstrate that interfacial modification via each dye leads to an increase in the absorption in the wavelength range of 300-1000 nm. Photoluminescence (PL) data prove that surface modification of CdS nanospheres with diverse dyes causes a decrease in the spectral intensity of PL curve, implying that efficient exciton separation is taking place upon dye loadings. Fabricated devices with and without modification show photovoltaic effects that can be seen from current density-voltage (J-V) curves obviously, and the highest power conversion efficiency (PCE) is obtained as 0.881% for N719-modified (ITO/CdS/N719/P3HT/Ag) device (almost 70-fold of pristine one) with a short-circuit current density (J(sc)) of 2.878mA/cm(2) and open-circuit voltage (V-oc) of 0.92V, respectively. This enhancement can be attributed to a better surface area between CdS and P3HT after dye modification.Öğe Facile synthesis and characterization of CdS thin films doped by yttrium atoms(Springer Heidelberg, 2023) Yilmaz, S.; Tomakin, M.; Polat, I.; Bacaksiz, E.A facile preparation and structural, optical and electrical characterization of undoped and Y-doped CdS thin films are demonstrated through spray pyrolysis changing doping concentration of yttrium atoms in CdS structure. X-ray diffraction pattern displays that CdS samples have polycrystalline hexagonal phase and as they are doped by various amounts of Y atoms, a fluctuation is observed in the preferential orientation. Scanning electron microscopy results show that compact and smooth surface morphology in addition to a slight reduction in grain size are obtained with increasing Y-doping up to 5%. Transparency of CdS thin films are noticeably enhanced by doping of 1% Y atoms. However, further increase of Y-doping towards 5% causes less transparent CdS films due to deterioration of crystal quality. Tauc analysis indicates presence of two direct bandgaps for each sample owing to spin-orbit splitting of valence band of CdS. CdS films have bandgaps of 2.48 eV (E-g1) and 2.85 eV (E-g2). Whereas E-g1 value decreases to 2.46 for 5% Y-doping, E-g2 value increases to 2.92 eV for the same Y-doping concentration. Photoluminescence data show that an obvious red shift is observed for blue band regardless of Y-doping concentration. 3% Y-doped CdS thin films display the best carrier density of 4.37 x 10(14) cm(-3) and resistivity of 3.78 x 10(3) & omega;.cm, which originate from substitutional incorporation of Y3+ ions at Cd2+ ions. Therefore, it can be stated that Y-doped CdS thin films exhibit better electrical and optical properties that are of vital importance in thin film-based solar cells as a window layer.Öğe Optical and electrical optimization of dysprosium-doped CdS thin films(Springer, 2018) Yilmaz, S.; Polat, I.; Tomakin, M.; Toreli, S. B.; Kucukomeroglu, T.; Bacaksiz, E.As-grown and Dy-doped CdS thin films containing concentrations of 1, 2, 3, 4 and 5 at.% Dy atom were prepared via chemical spray route on glass substrates. The constructed thin films were searched through analyzing their structural, morphological, optical and electrical features. X-ray diffraction (XRD) surveys showed that as-grown and Dy-doped CdS thin films had hexagonal structure and the preferential orientation was along (101) plane for as-grown, 1 and 2 at.% Dy-dopings. But further dopings (3 and 4 at.%) caused more random orientation, especially for the case of 5 at.%, the preferred orientation changed to (002) plane. The crystallite size progressively lessened from 39 to 27 nm with increasing Dy-doping. The existence of a close relation between grain shape and the preferential orientation appeared as compared to micrographs of scanning electron microscopy with XRD data. 5 at.% Dy-doped CdS thin films possessed the best transmittance (over 80%) among all the samples. Except for 2 at.% Dy-doped CdS sample, the other samples had almost a band gap of 2.45 eV. Photoluminescence results revealed that more stoichiometric thin films were formed after Dy-incorporations. The outcomes of the electrical investigation evidenced that the best sample was 1 at.% Dy-doped CdS thin films since the lowest resistivity (6.35 x 10(3) abroken vertical bar cm) and highest carrier concentration (1.06 x 10(14) cm(-3)) were obtained for this specimen.Öğe Performance assessment of oxygenated CdS films-based photodetector(Elsevier, 2024) Polat, I.; Yilmaz, S.; Kucukomeroglu, T.; Tomakin, M.; Bacaksiz, E.CdS films were grown by thermal evaporation on glass substrates. After growth process, samples were oxygenated at 400 degrees C at various gas pressures for 5 mins employing rapid thermal process. The produced CdS films were used as photodetectors in blue light. X-ray diffraction results revealed that as-deposited CdS films had a wurtzite crystal structure with a satrong preferred orientation along (002) plane. The intensity of (002) peak increased by rising oxygen gas pressure to 2 atm and then decreased with further increase of oxygen gas pressure to 4 atm. Scanning electron microscopy analysis indicated that even though as-deposited CdS thin films included some aligned rod-like grains on an underlaying layer, oxygenation at various gas pressures changed the surface morphology of CdS films. CdS films oxygenated at a gas pressure of 2 atm exhibited the best transmittance value of 80% in the range of 600-1000 nm. It was calculated that band gap increased from 2.42 eV to 2.45 eV as CdS films were oxygenated at a gas pressure of 2 atm. Photoluminescence spectrum of as-deposited CdS films indi-cated two fundamental peaks located at 530 nm and an interval of 550-700 nm, corresponding to green and deep level emissions, respectively. Consequently, it was attained that CdS films oxygenated at a pressure of 2 atm had the optimized structural, morphological and optical results and therefore, this sample was further employed for photodetecting applications. From photocurrent-time curves, the best photodetecting performance was reached for CdS films-based device oxygenated at a gas pressure of 2 atm including rise time and fall time values of 22 ms and 25 ms, respectively. In addition, the maximum responsivity, detectivity and external quantum efficiency were found to be 23.7 mA/W, 4.75 x 108 Jones and 6.6 for the same photodetector, respectively.Öğe Physical properties of CdS:Ga thin films synthesized by spray pyrolysis technique(Springer, 2017) Yilmaz, S.; Polat, I.; Olgar, M. A.; Tomakin, M.; Toreli, S. B.; Bacaksiz, E.This paper reports the investigation of physical properties of CdS:Ga thin films grown for the first time by a simple spray pyrolysis method as a function of Ga-doping level from 0 to 8 at.%. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive photoelectron spectroscopy, transmittance, photoluminescence, Hall effect and resistivity measurements are utilized to search for the structural, morphological, chemical, optical and electrical properties of as-prepared samples. XRD data confirm the presence of hexagonal structure with a strong (101) preferred orientation. SEM results show that the surface morphology varies significantly via Ga-doping, particularly 6 at.% doping level. Optical transparency is improved by the lower Ga-doping (2 and 4 at.%) whereas higher doping concentration (6 and 8 at.%) causes a poor transmission in the visible region. With respect to CdS (2.42 eV), the calculated band gap values at first enhances for 2 at.% Ga-doping and reaches to 2.43 eV. But, further increase in Ga-doping amount leads to a drop in the band gap value (2.39 eV) for 8 at.% Ga-doping. Electrical analyses display that 2 at.% Ga-doped CdS thin films exhibit a maximum carrier density and a minimum resistivity that are related to the substitutional incorporation of Ga3+ ions at Cd2+ ions. However, higher doping of Ga atoms into CdS gives rise to a gradual diminish in the carrier concentration and a rise in the resistivity. Based on all the data, it should be concluded that 2 at.% Ga-doped CdS thin films exhibit the best optical and electrical properties that can be used in the optoelectronic applications.Öğe Sm-doped CdS thin films prepared by spray pyrolysis: a structural, optical, and electrical examination(Springer, 2018) Yilmaz, S.; Polat, I.; Tomakin, M.; Kucukomeroglu, T.; Toreli, S. B.; Bacaksiz, E.Virgin and Sm-doped CdS thin films were prepared by spray pyrolysis route on glass substrates. The influences of Sm-doping amount on structural, topographical, optical and electrical properties were examined. It was found from X-ray diffraction data that virgin and 1 and 2 at.% Sm-doped CdS samples grew along (002) plane whereas the preferred orientation changed to (101) starting from Sm doping of 3 at.%. Morphological investigation showed that even though CdS specimen had irregular shaped grains, Sm-doping substantially modified the surface topography of CdS thin films. A maximum transmittance were attained for 4 at.% Sm-doped CdS sample. After Sm-doping, a slight increase was observed in the band gap value of CdS thin films. It was found from the room temperature photoluminescence data that compared to the virgin CdS, the intrinsic defect population of Sm-doped CdS thin films reduced, meaning that more stoichiometric films formed. From the electrical measurements, it was determined that 1 at.% Sm-doped CdS thin films exhibited the best electrical properties, i.e., maximum carrier density and minimum resistivity. Based on all the data, it could be pronounced that 4 at.% Sm-doped CdS displayed the best optical properties, whereas the optimum electrical characteristics were reached for 1 at.% Sm-doped CdS thin films.Öğe Structural, morphological, optical and electrical evolution of spray deposited ZnO rods co-doped with indium and sulphur atoms(Springer, 2014) Yilmaz, S.; Polat, I.; Atasoy, Y.; Bacaksiz, E.Undoped and (In-S) co-doped ZnO films were grown by the spray pyrolysis method on glass substrates. The structural, morphological, optical and electrical properties of all the samples were studied in detail. X-ray diffraction results showed that all the samples have a hexagonal wurtzite structure with the preferred orientation that changed from (002) to the random orientation after (In-S) co-doping. From the scanning electron microscopy analysis, it is noted that the morphology of ZnO changed from rods to thin film upon (In-S) co-doping. Compared to undoped ZnO rods, transparency of (In-S) co-doped ZnO thin films significantly increased whereas their band gap values gradually decreased. From photoluminescence measurements, it is observed that the UV peak completely quenched after (In-S) co-doping while the deep level band intensity slightly increased especially for 2 and 4 at.% (In, S) co-doped ZnO samples. Compared with undoped sample, the carrier concentration enhanced with the increase of (In-S) co-doping to 4 at.% and further increase in the co-doping amount results in the decline of the conductivity.Öğe Surface modification of CBD-grown CdS thin films for hybrid solar cell applications(Elsevier Gmbh, 2019) Yilmaz, S.; Unverdi, A.; Tomakin, M.; Polat, I.; Bacaksiz, E.The influences of interfacial modification by various dyes (Eosin-Y, D205, N719 and N3) on structural, morphological, optical and electrical properties of CdS-based hybrid solar cells are investigated. Structural properties showed the cubic growth of chemical bath deposited CdS thin films. Morphological analysis indicated that CdS specimen had a smooth and crack-free surface whereas P3HT layer coated on CdS thin films displayed spherical grains with nonuniform distribution. According to Tauc's estimation conclusions, CdS and P3HT layers exhibited band gaps of 2.98 eV and 1.98 eV, respectively. The surface modification of CdS thin films by diverse dyes led to an increase in the absorption spectra of the CdS samples. Photoluminescence data showed that surface treatment of CdS samples by diverse dyes caused a decrease in the luminescence intensity of the CdS-based hybrid solar cells, meaning that efficient exciton dissociation was obtained. All the devices showed an obvious photovoltaic effect as a result of current density voltage (J-V) curves. Furthermore, the highest solar cell efficiency was achieved for ITO/CdS/N3/Ag device as 0.322%, which could be ascribed to the surface modification of CdS thin films, giving rise to a formation of better interface between CdS and P3HT layers.Öğe Synthesis and fabrication of Mg-doped ZnO-based dye-sensitized solar cells (vol 25, pg 3173, 2014)(Springer, 2014) Polat, I.; Yilmaz, S.; Bacaksiz, E.; Atasoy, Y.; Tomakin, M.[Abstract Not Available]Öğe Synthesis and fabrication of Mg-doped ZnO-based dye-synthesized solar cells(Springer, 2014) Polat, I.; Yilmaz, S.; Bacaksiz, E.; Atasoy, Y.; Tomakin, M.Undoped and 2, 4 and 6 at.% Mg-doped ZnO nanorods were successfully deposited on ZnO seeded fluorine tin oxide substrates by a simple chemical bath deposition technique to form a photoanode. It was seen that all the samples had a hexagonal wurtzite structure with compact rod morphology. From Tauc's plot results, as compared to the undoped one (3.26 eV), the optical band gap of the ZnO:Mg samples increased to 3.32 eV for 4 at.% Mg-doping concentration and then decreased to 3.27 eV for 6 at.% Mg-doping. Photoluminescence results measured at 300 K indicated that ZnO nanorods had a ultra-violet peak with a wavelength of 382 nm, a blue peak at 420 nm and a deep level band in the range of 450-800 nm. Undoped and Mg-doped ZnO nanorods were subsequently used to realize ZnO-based dye-synthesized solar cells which exhibited the best power conversion efficiency of 0.144 % for 4 at.% ZnO:Mg sample.Öğe Transparent and conductive CdS:Ca thin films for optoelectronic applications(Springer Heidelberg, 2020) Yilmaz, S.; Polat, I.; Tomakin, M.; Bacaksiz, E.This paper presents the structural, morphological, optical and electrical evolution of Ca-doped CdS thin films. Non-doped and Ca-doped CdS samples with various amounts of Ca atoms (from 0 to 10 at.% with an increasing step of 2 at.%) were grown by spray pyrolysis route on glass slides. The structural investigation by X-ray diffraction showed that Ca-doping distorted CdS structure until 8 at.% Ca-doping and then a slight improvement in the intensity of (101) peak was obtained for 10 at.% Ca-doping compared to the other Ca-doping samples. Morphological analysis displayed a grain growth for a low amount of Ca-doping whereas higher concentration of Ca-doping led to a reduction in the grain size of CdS thin films. More stoichiometric CdS specimens were obtained after various amounts of Ca-doping according to energy dispersive X-ray spectroscopy data. Transparency of the CdS samples enhanced remarkably with the incorporation of Ca atoms in CdS with a particular concentration of 10 at.%. Tauc's plot investigation illustrated that the bandgap score of samples changed from 2.54 eV for non-doped CdS to 2.48 eV for 4 at.% Ca-doped CdS thin films. Further increase of Ca-doping doesn't vary the bandwidth of CdS samples. Photoluminescence data indicated that Ca-doped CdS thin films had lower intrinsic defects compared with non-doped CdS one. The electrical examination demonstrated that the carrier density of CdS thin films increased till 6 at.% Ca-doping and then decreased further increase of Ca-doping. However, resistivity values exhibited the opposite behavior accordingly. In conclusion, it can be pronounced that 6 at.% Ca-doped CdS thin films are the optimum specimen to be used as an effective transparent and conductive material in the optoelectronic devices.
