Browsing by Author "Parlak, Mehmet"
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Article Citation Count: 28Illumination and voltage effects on the forward and reverse bias current-voltage (I-V) characteristics in In/In2S3/p-Si photodiodes(Springer, 2021) Sürücü, Özge; Surucu, Ozge; Terlemezoglu, Makbule; Parlak, Mehmet; Altindal, Semsettin; Electrical-Electronics EngineeringThe illumination and voltage effects on the I-V measurements of the fabricated In/In2S3/p-Si photodiode were investigated in dark and under various illumination intensities (20-100 mW/cm(2)) between +/- 2 V. Two linear regions in the forward-bias ln(I)-V plots were observed. The value of diode ideality factor (n) had an increasing trend with increasing illumination intensity while the barrier height (phi(Bo)) had a decreasing trend due to the increase of photocurrent. The photodiode properties were also investigated, and the value of linear-dynamic value range (LDR) was found to be 20.56 dB. The photoresponse (I-ph/I-dark), the photoresponsivity (R), and specific detectivity (D*) of the photodiode were calculated as a function of the illumination. The open-circuit voltage (V-oc) and short-current (I-sc) were found to be 0.36 V and 2.87 mA under 100 mW.cm(-2) illumination intensity, respectively. The possible conduction mechanisms (CMs) were investigated using the forward ln(I)-V and reverse ln(I)-V-0.5 plots. The energy-dependent surface states (N-ss) profile was extracted from the positive I-V data by considering voltage-dependent barrier height (BH) and ideality factor (n) in dark and illumination at 100 mW/cm(2).Article Citation Count: 0Nanowire geometry effects on devices and transport mechanisms: SnS2/SiNW heterojunction(Springer, 2023) Coskun, Emre; Emir, Cansu; Terlemezoglu, Makbule; Parlak, MehmetThe semiconductor nanowire technology has become essential in developing more complex and efficient devices. In this study, the Si nanowire (SiNW) heterojunction structure with a two-dimensional SnS2 thin film was investigated. The SiNW array was created by the metal-assisted etching method because of length control and production over large areas of nanowires. The created SiNW has more diminishing reflectivity compared with Si planar substrate. The diode characteristics of SnS2/SiNW and SnS2/Si planar heterojunctions were investigated by dark current analysis at room temperature, and the improving diode characteristics by the three-dimensional interface between SiNW and SnS2 thin film were discussed. Transport mechanisms of the SiNW heterojunction were also studied for various methods. Thermionic emission and thermally assisted tunneling models are the dominant mechanisms for low voltages (0.02-0.20 V), and the space charge limiting current mechanism dominates the current for comparingly high voltages (0.20-0.40 V). All the values reveal the significant impact of the SiNW on heterojunctions for improving efficiency.Article Citation Count: 0A new method to determine the continuous refractive index of an absorbing film by Generalized Stockwell Transform(Elsevier Sci Ltd, 2023) Coskun, Emre; Emir, Cansu; Selamet, Semanur; Parlak, Mehmet; Ozder, SerhatGeneralized Stockwell Transform (GST) was adapted to analyze a transmittance signal to continuously determine the refractive index and extinction coefficient. The process is built by analyzing oscillation frequencies of the transmission signal where oscillations exist. The simulation studies clearly show the advantage of the locally referenced phase property of the presented method. The validity of the method was checked for a CdS thin film. The results determined by the GST method are consistent with the results determined by envelope and other signal analyzing methods, and the literature. The noise and relative error analysis of the method was also discussed.Article Citation Count: 0Performance analysis of CuSbSe2 thin-film solar cells with Cd-free window layers(Elsevier, 2024) Sürücü, Özge; Bal, Ersin; Gencer, Aysenur; Parlak, Mehmet; Surucu, Ozge; Electrical-Electronics EngineeringThis study investigates novel thin-film solar cells featuring CuSbSe2 (CASe) with ZnSnO and ZnMgO windows in the layer superstrate structure. For glass/ITO/ZnMgO/CASe/Cu + Au, the J-V measurements reveal a shortcircuit current density (Jsc) of 19.4 mA/cm2, an open-circuit voltage (Voc) of 0.28 Volts, a fill factor (FF) of 39.14 %, and a power conversion efficiency (eta) of 2.13 %. Similarly, glass/ITO/ZnSnO/CASe/Cu + Au exhibits Jsc around 19.6 mA/cm2, Voc around 0.31 Volts, FF around 40 %, and eta of 2.43 %. This paper is a pioneering contribution, introducing novel thin-film solar cells with a distinctive superstrate structure utilizing CASe in conjunction with ZnSnO and ZnMgO windows. The comprehensive study presents the first-ever characterization and performance evaluation of these innovative configurations, shedding light on their unique potential in advancing sustainable solar energy technology.Article Citation Count: 1Physical characterization of thermally evaporated Sn-Sb-Se thin films for solar cell applications(Springer Heidelberg, 2023) Sürücü, Özge; Surucu, Ozge; Terlemezoglu, Makbule; Parlak, Mehmet; Electrical-Electronics EngineeringThe substitution of Sb in binary SnSe structure may lead to tailoring the physical properties of both SnSe and SbSe, promising absorber layers for thin film solar cells. The resulting Sn-Sb-Se structure could be an outstanding material for photovoltaic applications. In this study, Sn-Sb-Se thin films were deposited by thermal evaporation, and the effect of annealing on the films' structural, optical, and electrical properties were reported. XRD measurement shows that annealing at 300 degrees C yields the best crystalline quality, and structural parameters were calculated using XRD data. SEM and AFM measurements indicate deformation in the film surface after annealing at 400 degrees C. UV-Vis spectroscopy measurement provides a high absorption coefficient which indicates a direct band gap. The band gap and activation energies of the as-grown sample were found as 1.59 eV and 106.1 meV, respectively. The results of SEM, AFM, XRD, Raman, UV-Vis spectroscopy and temperature-dependent photoconductivity measurements were discussed throughout the paper.Article Citation Count: 13Structural, morphological and temperature-tuned bandgap characteristics of CuS nano-flake thin films(Elsevier, 2022) Işık, Mehmet; Terlemezoglu, Makbule; Gasanly, Nizami; Parlak, Mehmet; Department of Electrical & Electronics EngineeringCopper sulfide (CuS) thin films were produced by radio-frequency (RF) magnetron sputtering method. Structural, morphological and optical characteristics of deposited CuS films were presented. X-ray diffraction pattern showed two intensive peaks associated with hexagonal crystalline structure. Scanning electron microscopy image indicated that CuS films have nano-flake structured. Raman spectrum was reported to show vibrational characteristics of the CuS nano-flake thin films. Two peaks associated with Cu-S and S-S vibrations were observed in the Raman spectrum. Transmission spectra were recorded at various temperatures between 10 and 300 K. The analyses accomplished considering Tauc expression demonstrated that direct bandgap energy decreases from 2.36 eV (at 10 K) to 2.22 eV (at 300 K). Temperature-bandgap dependency was analyzed considering Varshni and Bose-Einstein expressions to reveal bandgap at 0 K, rate of change of bandgap and Debye temperature. CuS nanoflake thin film may be used in optoelectronic and photocatalysis applications thanks to its direct and narrow bandgap energy characteristics.