Browsing by Author "Surucu, O. Bayrakli"
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Article Citation Count: 6Construction of self-assembled vertical nanoflakes on CZTSSe thin films(Iop Publishing Ltd, 2019) Sürücü, Özge; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Abak, M. K.; Gullu, H. H.; Ercelebi, C.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringCu2ZnSn(S, Se)(4) (CZTSSe) is a promising alternative absorber material to achieve high power conversion efficiencies, besides its property of involving low-cost and earth-abundant elements when compared to Cu(In, Ga) Se-2 (CIGS) and cadmium telluride (CdTe), to be used in solar cell technology. In this study, a novel fabrication technique was developed by utilizing RF sputtering deposition of CZTSSe thin films having a surface decorated with self-assembled nanoflakes. The formation of nanoflakes was investigated by detailed spectroscopic method of analysis in the effect of each stacked layer deposition in an optimized sequence and the size of nanoflakes by an accurate control of sputtering process including film thickness. Moreover, the effects of substrate temperature on the formation of nanoflakes on the film surface were discussed at a fixed deposition route. One of the main advantages arising from the film surface with self-assembled nanoflakes is the efficient light trapping which decreases the surface reflectance. As a result of the detailed production and characterization studies, it was observed that there was a possibility of repeatable and controllable fabrication sequence for the preparation of CZTSSe thin films with self-textured surfaces yielding low surface reflectance.Article Citation Count: 9CZTSSe thin films fabricated by single step deposition for superstrate solar cell applications(Springer, 2019) Sürücü, Özge; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Gullu, H. H.; Ciftpinar, E. H.; Ercelebi, C.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringThe focus of this study is the characterization of Cu2ZnSn(S,Se)(4) (CZTSSe) thin films and fabrication of CZTSSe solar cell in superstrate configuration. In this work, superstrate-type configuration of glass/ITO/CdS/CZTSSe/Au was entirely fabricated by totally vacuum-based process. CZTSSe absorber layers were grown by RF magnetron sputtering technique using stacked layer procedure. SnS, CuSe and ZnSe solid targets were used as precursors and no additional step like the selenization process was applied. The structural and morphological properties of deposited CZTSSe layers were analyzed using X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy analysis (EDS) measurements. The optical and electrical properties of the CZTSSe thin films were investigated by UV-Vis spectroscopy, Hall-Effect and photoconductivity measurements. In addition, the device performance of the fabricated superstrate solar cell was examined.Article Citation Count: 21Determination of current transport characteristics in Au-Cu/CuO/n-Si Schottky diodes(Elsevier, 2019) Sürücü, Özge; Gullu, H. H.; Güllü, Hasan Hüseyin; Yildiz, D. E.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringIn this study, the material properties of CuO thin films fabricated by sputtering technique and electrical properties of CuO/n-Si structure were reported. Temperature-dependent current-voltage (I-V) measurement was carried out to determine the detail electrical characteristics of this structure. The anomaly in thermionic emission (TE) model related to barrier height inhomogeneity at the interface was obtained from the forward bias I-V analysis. The current transport mechanism at the junction was determined under the assumption of TE with Gaussian distribution of barrier height. In this analysis, standard deviation and mean zero bias barrier height were evaluated as 0.176 and 1.48 eV, respectively. Depending on the change in the diode parameters with temperature, Richardson constant was recalculated as 110.20 Acm(-2)K(-2) with the help of modified Richardson plot. In addition, density of states at the interface were determined by using the forward bias I-V results.Article Citation Count: 14Frequency effect on electrical and dielectric characteristics of In/Cu2ZnSnTe4/Si/Ag diode structure(Springer, 2019) Sürücü, Özge; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Yildiz, D. E.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringIn/Cu2ZnSnTe4/Si/Ag diode structure was fabricated by sputtering Cu2ZnSnTe4 (CZTTe) thin film layer on the Si layer with In front contact. The frequency dependent room temperature capacitance and conductance measurements were carried out to obtain detailed information of its electrical characteristics. Admittance spectra of the diode exhibited strong frequency dependence and the obtained values showed decreasing behavior with the increase in the applied frequency. The effect of interfacial film layer with series resistance values and density of interface states were investigated by taking into consideration of non-ideal electrical characteristics of the diode. The distribution profile of the interface states was extracted by Hill-Coleman and high-low frequency capacitance methods. As a function of frequency, they were in proportionality with the inverse of applied frequency. Dielectric constant and dielectric loss parameters were calculated from the maximum value of the diode capacitance at the strong accumulation region. The loss tangent showed a characteristic peak behavior at each frequency. Based on the time-dependent response of the interfacial charges to the applied ac field, the values of ac electrical conductivity and complex electric modulus were calculated and discussed as a function of frequency and bias voltage.Article Citation Count: 10Investigation of band gap energy versus temperature for SnS 2 thin films grown by RF-magnetron sputtering(Elsevier, 2020) Sürücü, Özge; Gullu, H. H.; Işık, Mehmet; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Gasanly, N. M.; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering[No Abstract Available]Article Citation Count: 11Investigation of electrical characteristics of Ag/ZnO/Si sandwich structure(Springer, 2019) Sürücü, Özge; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Yildiz, D. E.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringIn this study, temperature-dependent current-voltage (I-V), frequency-dependent capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements are carried out for the electrical characterization of a zinc oxide (ZnO) thin film-based diode. The sandwich structure in the form of Ag/ZnO/Si/Al is investigated at temperatures between 220 and 360 K and in the frequency region of 1 kHz-1 MHz. ZnO thin film layer is deposited on a p-Si wafer substrate as a transparent conductive oxide layer by taking into consideration possible electronic applications with intrinsic attractive material properties. At each temperature step, the I-V curves showed about two orders of magnitude rectifying behavior and, according to the Schottky diode relation, the saturation current, zero-bias barrier height and ideality factor were extracted as a function of the temperature. In the case of non-ideal diode characteristics due to the inhomogeneties in the diode as observed from the characteristics of the calculated parameters, effective barrier height values are evaluated. In addition, based on the existence of the interface layer, density of interface states in the band gap region and parasitic resistances were determined by the capacitance measurements.Article Citation Count: 5Material and Si-based diode analyses of sputtered ZnTe thin films(Springer, 2020) Sürücü, Özge; Surucu, O. Bayrakli; Işık, Mehmet; Terlemezoglu, M.; Güllü, Hasan Hüseyin; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringStructural, optical, and electrical properties ZnTe thin films grown by magnetron sputtering technique were studied by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and electrical conductivity measurements. Structural analyses showed that ZnTe thin films grown on soda-lime glass substrates have a cubic crystalline structure. This crystalline nature of the films was also discussed in terms of Raman active modes. From atomic force microscopy images, the smooth and dense surface profile was observed. The conductivity of the film at room temperature was measured as 2.45 x 10(-4)(omega cm)(-1)and the temperature dependency of conductivity showed Arrhenius behavior. The dark conductivity profile was modeled by thermionic emission mechanism and activation energies were extracted. In addition, the conductivity values indicated an increasing behavior with illumination intensity applied between 20 and 115 mW/cm(2). The heterojunction diode was generated by sputtering ZnTe film on n-Si wafer substrate and the rectification behavior was evaluated to determine the main diode parameters.Article Citation Count: 17Temperature dependence of band gaps in sputtered SnSe thin films(Pergamon-elsevier Science Ltd, 2019) Sürücü, Özge; Isik, M.; Işık, Mehmet; Terlemezoglu, M.; Güllü, Hasan Hüseyin; Parlak, M.; Gasanly, N. M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringTemperature-dependent transmission experiments were performed for tin selenide (SnSe) thin films deposited by rf magnetron sputtering method in between 10 and 300 K and in the wavelength region of 400-1000 nm. Transmission spectra exhibited sharp decrease near the absorption edge around 900 nm. The transmittance spectra were analyzed using Tauc relation and first derivative spectroscopy techniques to get band gap energy of the SnSe thin films. Both of the applied methods resulted in existence of two band gaps with energies around 1.34 and 1.56 eV. The origin of these band gaps was investigated and it was assigned to the splitting of valence band into two bands due to spin-orbit interaction. Alteration of these band gap values due to varying sample temperature of the thin films were also explored in the study. It was seen that the gap energy values increased almost linearly with decreasing temperature as expected according to theoretical knowledge.Article Citation Count: 14Temperature dependence of electrical properties in In/Cu2ZnSnTe4/Si/Ag diodes(indian Acad Sciences, 2019) Sürücü, Özge; Yildiz, D. E.; Güllü, Hasan Hüseyin; Terlemezoglu, M.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringCu2ZnSnTe4 (CZTTe) thin films with In metal contact were deposited by thermal evaporation on monocrystalline n-type Si wafers with Ag ohmic contact to investigate the device characteristics of an In/CZTTe/Si/Ag diode. The variation in electrical characteristics of the diode was analysed by carrying out current-voltage (I-V) measurements in the temperature range of 220-360 K. The forward bias I-V behaviour was modelled according to the thermionic emission (TE) theory to obtain main diode parameters. In addition, the experimental data were detailed by taking into account the presence of an interfacial layer and possible dominant current transport mechanisms were studied under analysis of ideality factor, n. Strong effects of temperature were observed on zero-bias barrier height (Phi(B0)) and n values due to barrier height inhomogeneity at the interface. The anomaly observed in the analysis of TE was modelled by Gaussian distribution (GD) of barrier heights with 0.844 eV mean barrier height and 0.132 V standard deviation. According to the Tung's theoretical approach, a linear correlation between Phi(B0) and n cannot be satisfied, and thus the modified Richardson plot was used to determine Richardson constant (A*). As a result, A* was calculated approximately as 120.6 A cm(-2) K-2 very close to the theoretical value for n-Si. In addition, the effects of series resistance (R-s) by estimating from Cheng's function and density of surface states (N-ss) by taking the bias dependence of effective barrier height, were discussed.Article Citation Count: 8Temperature dependent band gap in SnS2xSe(2-2x) (x=0.5) thin films(Elsevier Sci Ltd, 2020) Sürücü, Özge; Isik, M.; Işık, Mehmet; Terlemezoglu, M.; Güllü, Hasan Hüseyin; Gasanly, N. M.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringStructural and optical properties of SnS2xSe(2-2x) thin films grown by magnetron sputtering method were investigated for composition of x = 0.5 (SnSSe) in the present study. X-ray diffraction, energy dispersive X-ray spectroscopy, atomic force microscopy and scanning electron microscopy methods were used for structural characterization while temperature-dependent transmission measurements carried out at various temperatures in between 10 and 300 K were accomplished for optical investigations. X-ray diffraction pattern of studied composition presented peaks at positions which are between those of SnSe2 and SnS2. Transmittance spectra recorded at all applied temperatures were analyzed using well-known Tauc relation. Analyses revealed the direct band gap energy value of SnSSe thin films as 1.75 eV at room temperature. Change of band gap energy as a response to varying temperature were discussed in the study by utilizing Varshni relation. It was shown that variation of gap energy values was well-matched with the Varshni's empirical formula. Energy band gap at absolute zero and rate of change of band gap with temperature were found to be 1.783 eV and -2.1 x 10(-4) eV K-1, respectively.