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Öğe Alloying and phase transformation in CdS/CdSe bilayers annealed with or without CdCl2(Elsevier Sci Ltd, 2019) Ciris, A.; Basol, B. M.; Yilmaz, S.; Atasoy, Y.; Tomakin, M.; Kucukomeroglu, T.; Bacaksiz, E.The present paper studies the structural, compositional, morphological and optical properties of thin CdS/CdSe stacks annealed in an inert atmosphere or subjected to a CdCl2 treatment. The bilayer stacks were fabricated by chemical bath deposition (CBD) of a 50 nm thick CdS layer followed by evaporation of a CdSe film with equal thickness. It was found that when this stack was annealed at 400 degrees C for up to 10 min, no appreciable intermixing/alloying between the two layers was detected. Upon heating for 5-10 min in presence of a CdCl2 layer disposed over the CdSe film, however, led to appreciable alloying and formation of CdSSe, which was confirmed through XRD, optical transmission and room temperature photoluminescence measurements. XRD data further showed that the CdS layer in the CdS/CdSe stack had nano-amorphous structure that did not change upon annealing in inert atmosphere. The CdSe layer of the stack, which had a cubic structure, also preserved its phase upon annealing in inert atmosphere. When the CdS/CdSe stack was CdCl2 treated, the phase of the CdSSe alloy formed was transformed to hexagonal. These observations may have consequences in applications where CdS/CdSe bilayers are formed within device structures and subjected to various types of heat treatments.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 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 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.
