Suleyman Ozcelik | Gazi University (original) (raw)

Papers by Suleyman Ozcelik

Journal of Materials Science: Materials in Electronics, Jun 1, 2023

Optical and Quantum Electronics, Jun 21, 2018

DJ GaInP/GaAs SC structure was designed by using analytical solar cell model. The electrical para... more DJ GaInP/GaAs SC structure was designed by using analytical solar cell model. The electrical parameters (J sc , V oc , FF and η) were calculated by determining optimum conditions for improving the performance of the SCs. Considering the optimization conditions in design of SC, lattice and current matched DJ GaInP/GaAs SC structure was grown using MBE technique. Alloy composition and lattice constants of each layers in the structure were estimated from measured XRD data. To evaluate of effects on conversion efficiency of different metal contact materials, SC devices were fabricated by photolithographic technique. Two types of front-side electrodes, which included Au and Au/Ti metals, were separately fabricated on devices and denoted as S1 and S2, respectively. Performance of the S1 and S2 were determined using I-V measurements under the AM1.5 illuminations. S2 possesses 4.16% enhancement in conversion efficiency compared to that of S1. The better performance of the S2 can be attributed to having higher I sc and V oc due to higher conductivity of titanium as well as good adhesion on GaAs. In addition, Al 2 O 3 /TiO 2 anti-reflective coating effect on performance of the S1 and S2 was also investigated. Sputtered anti-reflective layer increased the efficiencies from 14.65 to 15.72% and 15.26 to 16.90% for S1 and S2, respectively.

Journal of Materials Science: Materials in Electronics, Apr 1, 2023

Social Science Research Network, 2022

Scientific Reports, Nov 12, 2022

Semi-transparent organic solar cells' (ST-OSCs) photovoltaic and high optical performance paramet... more Semi-transparent organic solar cells' (ST-OSCs) photovoltaic and high optical performance parameters are evaluated in innovative applications such as power-generating windows for buildings, automobiles, and aesthetic designs in architectural and industrial products. These parameters require the precision design of structures that optimize optical properties in the visible region and aim to achieve the required photon harvest in UV and IR. These designs can be realized by integrating wavelength-selective photonics-based systems into ST-OSC to increase localized absorption in wavelengths greater than 600 nm and NIR and provide modifiable optical properties. In this study, methodologically, we followed highly detailed light management engineering and transfer matrix method-based theoretical and experimental approaches. We discussed the optimal structures by evaluating color, color rendering index, correlated color temperature, and photovoltaic performances for ST-OSCs, including one-dimensional photonic crystal (1D-PC) designed at different resonance wavelengths (λ B) and periods. Finally, by integrating fine-tuned (MgF 2 /MoO 3) N 1D-PC, we report the inherently dark purple-red color of the P3HT:PCBM bulk-heterojunction-based ST-OSC neutralizes with the optimal state was 0.3248 and 0.3733 by adjusting close to the Planckian locus. We also enhanced short current density from 5.77 mA/cm 2 to 6.12 mA/cm 2 and PCE were increased by 7.34% from 1.77% to 1.90% designed for the N = 4 period and λ B = 700 nm. The features of organic semiconductor-based photovoltaic (PV) technology, such as lightness, thinness and flexibility, cost-effective production, sustainability, and simple fabrication processes, make them stand out among other photovoltaic technologies both in academic studies and in the industry 1-5. In particular, the efficiency of organic solar cells (OSC), reaching over 18% in the past few years, has increased the application potential of many new PV systems, which are designed 1,2,6-10. At the forefront of these new photovoltaic systems are colored, transparent and semi-transparent OSCs (ST-OSC), which present the most striking properties of organic materials 1,3,11. Recently, researchers have especially focused on their potential applications in flexible or semi-transparent solar cells due to the flexible nature of their active layers and the strong absorption coefficient of organic photoactive materials rather than aiming for high cell efficiency 1,6,12,13. Usually, the active layer of the solar cell is designed to absorb light outside the visible range (380-780 nm) (VR) while maintaining high transparency in VR for ST requirements 14. However, ST requirements can be achieved by adding different photonic and material systems to the structure without changing the structure of the organic material forming the active region 1. In addition, developing high-conductivity transparent contact systems to reduce absorption and reflection in visible light without disturbing the selective transport and band arrangement is a critical parameter in designing high-performance ST-OSCs 13. In OSCs, opaque metal electrodes

Scientific Reports, Jul 4, 2022

Photonic-based functional designs and integrations for advanced optoelectronic devices are regard... more Photonic-based functional designs and integrations for advanced optoelectronic devices are regarded as promising candidates considering the enhancement of efficiency and tunability. With the aim to improve photovoltaic performance by increasing photon harvesting, the study presents the prominent findings of experimental and theoretical comparison of optical and electrical evaluation integrating a functionally designed one-dimension photonic crystal (1D-PC) into CdTe solar cells. Since transparency of the CdS/CdTe heterojunction based solar cell (SC) is reduced by a photonic band gap formed by (MgF 2 /MoO 3) N 1D-PC; namely, re-harvesting is improved by increasing absorbance. The period number at resonance wavelength of 850 nm and photocurrent density (J ph) have remarkable influence on the investigation. For four periods, the reflectance in the region of photonic band gap is sufficient for photon harvesting and saturation occurs. The photovoltaic performances are comparatively analysed for SCs with and without 1D-PC produced at optimal values. The open-circuit voltage does not change, besides, short-circuit current density and maximum-current density vary between 15.86-17.23 mA cm −2 and, 13.08-15.41 mA cm −2. Having integrated the 1D-PC into the structure, it is concluded that the FF and power conversion efficiency increase from 55.27 to 63.35% with an improvement of 15.91% and, from 8.26 to 10.47% with an improvement of 21.10%. In today's world, where the increasing energy demand is high, the importance of the energy need for abundant, low-cost, and clean energy sources is increasing day by day. Therefore, renewable energy, an alternative to fossil fuel-containing sources, offers a solution to overcome this energy need. In solar cells (SC), which are the most promising alternative among renewable energy sources, photon energy from the sun can be collected cheaply, efficiently, and simply 1. Especially Cadmium Tellurium (CdTe) based solar cells have recently attracted attention in academic and industrial studies due to their ability to reach 22.1% efficiencies 2,3 , high thermal cell stability, low cost, and long-term stable photovoltaic performance 4-7. CdTe has a direct optical band gap around 1.45 eV, which is the convenient band gap for SC's. Also, due to the high absorbency of CdTe, CdTe-based SCs generally consist of a thin n-type Cadmium Sulfide (CdS) and a relatively thick p-type CdTe heterojunction. The efficiency of CdS/CdTe heterojunction SCs has been increased by 1.5% in the last 20 years under laboratory conditions, with cell efficiency exceeding 20% and module efficiency close to 15% 8-10. Through the absorber CdTe, which provides high absorption at the joint, all photons with energies greater than the band gap can be absorbed even with a very thin p-type material. SCs based on CdS/CdTe heterojunctions with a CdTe absorber layer about 2 μm thick can absorb almost all photons from AM 1.5G. In addition, the flexibility of the CdS/CdTe heterojunction at this thickness is quite high. For this reason, the use of CdS/CdTe-based SCs in technology is very advantageous in terms of production, mechanical functionality, and lightness. The n-type CdS layer is a suitable thin window layer in the heterojunction and can form a suitable

Journal of Electronic Materials, Sep 17, 2018

The structural, optical, electrical and electrical-optical properties of a doublejunction GaAsP l... more The structural, optical, electrical and electrical-optical properties of a doublejunction GaAsP light-emitting diode (LED) structure grown on a GaP (100) substrate by using a molecular beam epitaxy technique were investigated. The p-n junction layers of GaAs 1Àx P x and GaAs 1Ày P y , which form the doublejunction LED structure, were grown with two different P/As ratios. Highresolution x-ray diffraction (HRXRD), photoluminescence (PL), and currentvoltage (I-V) measurements were used to investigate the structural, optical and electrical properties of the sample. Alloy composition values (x, y) and some crystal structure parameters were determined using HRXRD measurements. The phosphorus compositions of the first and second junctions were found to be 63.120% and 82.040%, respectively. Using PL emission peak positions at room temperature, the band gap energies (E g) of the first and second junctions were found to be 1.867 eV and 2.098 eV, respectively. In addition, the alloy compositions were calculated by Vegard's law using PL measurements. The turn-on voltage (V on) and series resistance (R s) of the device were obtained from the I-V measurements to be 4.548 V and 119 X, respectively. It was observed that the LED device emitted in the red (664.020 nm) and yellow (591.325 nm) color regions.

Journal of Alloys and Compounds

A two-step process was used to prepare Cu2SnS3 films in this study: first, precursor stacks were ... more A two-step process was used to prepare Cu2SnS3 films in this study: first, precursor stacks were deposited using a magnetron sputtering technique, and then the stacks were annealed in sulfur-containing atmosphere at various times. Utilizing a variety of characterization techniques, it was thoroughly examined how sulfurization time affected the films’ structural, morphological, optical, and electrical characteristics. X-ray diffraction and Raman spectroscopy measurements indicated that two structural polymorphs (tetragonal and monoclinic) of Cu2SnS3 co-existed in the films. Surface and cross-sectional images obtained by scanning electron microscopy showed that the microstructures of the films were entirely changed to well-grown crystal structures at 30 min and 40 min sulfurization times. In2S3/Cu2SnS3 stacks were prepared by the deposition of In2S3 films on the absorber layers sulfurized for 30 and 40 min by RF magnetron sputtering method. The fabrication of Ni/Al/Ni/AZO/i:ZnO/In2S3/Cu2SnS3/Mo/SLG-structured devices was done using both thermally annealed and non-annealed In2S3/Cu2SnS3 stacks. Secondary ion mass spectroscopy studies of the devices revealed that the indium diffused from In2S3 layer into the Cu2SnS3 absorber to a certain depth. The efficiency values of the devices were found to have been slightly enhanced with the annealing of the In2S3/Cu2SnS3 stacks. The solar cell with the maximum efficiency (η) of 3.12 %, open-circuit voltage (VOC) of 0.265 mV, short-circuit current (JSC) of 37.90 mA/cm2, and fill factor (FF) of 0.31 was produced by thermally annealed In2S3/Cu2SnS3 stack with an absorber layer sulfurized for 40 min.

Thin Solid Films, 2020

In this work, Cu 2 ZnSnS 4 (CZTS) absorber films were prepared by sulfurization of co-sputtered p... more In this work, Cu 2 ZnSnS 4 (CZTS) absorber films were prepared by sulfurization of co-sputtered precursor films at different time periods. The influence of sulfurization time on physical characteristics of the grown films was investigated in detail. The sulfurized CZTS films exhibited the characteristic diffraction peak of the kesterite phase corresponding to the (112) crystal plane, the main Raman mode of kesterite phase at around 337 cm −1 and Cu-deficient and Zn-rich composition. From the atomic force microscopy surface and cross-sectional scanning electron microscopy images, it was revealed out that the films were uniform, compact without any cracks and consisted of micron-sized and closely packed grains. In addition, the films showed tail-to-tail, band-to-tail and band-to-band transitions at around 1.41 eV (E 1), 1.45 eV (E 2) and 1.51 eV (E 3), respectively. Secondary ion mass spectroscopy analysis showed that the sodium ions deeply diffused through the molybdenum layer into the CZTS film from the soda lime glass substrate for all samples. All of the films exhibited an optical band gap of around 1.4 eV, an absorption coefficient over 10 4 cm −1 , p-type conductivity with a high concentration of free holes in the order of 10 17-10 18 cm −3 and low mobility in the range from 0.63 cm²/V.s to 8.11 cm²/V.s.

Journal of Electronic Materials, 2021

Here we report the growth of molybdenum disulfide (MoS 2) films with different thicknesses on sil... more Here we report the growth of molybdenum disulfide (MoS 2) films with different thicknesses on silicon dioxide/silicon (SiO 2 /Si) and c-plane sapphire substrates by sulfurization of direct current (DC) sputtered Mo precursor films in a chemical vapor deposition furnace with sulfur powder at 900°C. The structural, morphological, optical, and electrical properties of the films on different substrates were investigated through a series of characterization in detail. X-ray diffraction (XRD) results showed that the grown films on sapphire substrates had better crystallization and a well-stacked layered structure than the films on SiO 2 /Si substrates. The frequency difference between the characteristic modes E 1 2g and A 1g of hexagonal phase MoS 2 was determined as $ 26 cm À1 which is consistent with the typical value of bulk MoS 2. Energy-dispersive x-ray (EDX) spectra exhibited that the films were near-stoichiometric. A small shift towards the lower binding energies in the Mo 3d 5/2 peak positions was observed due to the valency of Mo below +4 depending on the compositional ratios of the films in xray photoelectron spectroscopy (XPS) spectra. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis indicated that the films had smooth surfaces and a well-packed crystal structure. However, when the thickness of the films deposited on sapphire substrates increased, the strain between the sapphire substrate and MoS 2 film caused the formation of the micro-domes in the film. In addition, the films exhibited high absorption and reflection properties in the near-infrared (NIR) and mid-infrared (MIR) regions in Fourier transform infrared (FTIR) analysis. Therefore, it is considered that the films can be used for photodetector applications in these regions and infrared shielding coating applications.

Vacuum, 2020

In the current study, silicon was utilized as the substrate material and, then, the TiO 2 deposit... more In the current study, silicon was utilized as the substrate material and, then, the TiO 2 depositions with 100 nm, 300 nm, 500 nm and 700 nm were done onto substrates as thin films at room temperature by a radio frequency (rf) magnetron sputtering method. The binding energy, the surface roughness, elemental analysis and the specific acoustic impedance have been determined via X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and scanning acoustic microscopy (SAM), respectively. AFM analysis represented that the root mean square roughness values changed in the range of 0.72 nm-1.22 nm, gradually by the increase in thickness. Two-dimensional acoustic images were recorded by SAM with 80 MHz transducer. The mean and standard deviation values of acoustic impedance were found as 3.151 ± 0.080 MRayl for 100 nm, 3.366 ± 0.080 MRayl for 300 nm, 3.379 ± 0.067 MRayl for 500 nm and, 3.394 ± 0.065 MRayl for 700 nm. SAM results pointed out that the hardness of films increased with increasing thickness. Moreover, the surface defects at the micrometer level were demonstrated. The success of imaging films indicated the potential of SAM in monitoring as well as the inspection of flat two-dimensional surfaces.

Solar Energy, 2021

Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zi... more Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

International Journal of Energy Research, 2020

This paper reports the plasma discharge analysis of a dielectric barrier discharge (DBD) source. ... more This paper reports the plasma discharge analysis of a dielectric barrier discharge (DBD) source. Helium is used as a working gas. The analysis is performed at fixed working pressure and operating frequency. The investigations are carried out using sinusoidal supply for the generation of discharges where two current pulses have been observed with different polarities in one period. A homogeneous type of discharge has been observed for different operating conditions in this DBD source. Since in situ diagnostics are not possible due to the small geometries in the used DBD source, the electrical measurements and spectroscopic analysis of the discharge have been performed to analyse the plasma discharge. The electrical analysis has been carried out using equivalent electrical circuit model. The plasma density and temperature within the discharge have been estimated using line ratio technique of the observed visible neutral helium lines. The estimated electron plasma density is found to be in close proximity with the plasma simulation code 'OOPIC Pro'.

IEEE Sensors Journal, 2020

The goal of in this paper has to design, fabricate and test gas sensors based on chromium (Cr) do... more The goal of in this paper has to design, fabricate and test gas sensors based on chromium (Cr) doped titanium dioxide (TiO2) thin films for propane gas detection. Cr doped TiO2 thin films with different power on the Cr target ranging from 5 to 20 W were deposited by confocal magnetron sputtering at same deposition conditions. The effect of Cr concentrations on structural, morphological and optical properties of the films have been investigated in detail. The thin film characterizations were performed by using X-Ray Photoelectron Spectroscopy (XPS), Energy-Dispersive X-Ray Spectroscopy (EDX), Secondary Ion Mass Spectroscopy (SIMS), Atomic Force Microscope (AFM), UV-Vis-NIR spectrometer and Photoluminescence (PL) systems. The sensing behavior of the sensors was tested with gas testing system to propane gas at 250, 500 and 1000 ppm. The high sensor performance was observed in gas detection behavior with increasing Cr content. In particular, the obtained gas sensor with Cr RF power of 20 W exhibited higher sensor response in the detection of propane at working temperature of 300 °C.

Journal of Materials Science: Materials in Electronics, 2020

In this study, temperature-and frequency-dependent capacitance and conductance measurements of th... more In this study, temperature-and frequency-dependent capacitance and conductance measurements of the Au/SrTiO 3 /p-Si heterojunction structure were examined. Strontium titanate (SrTiO 3) thin films were deposited on cleaned p-type (100)-oriented silicon substrates using radio frequency (RF) magnetron sputtering method at a substrate temperature of 500 °C. The temperature-dependent reverse and forward bias C-V and G/ω−V characteristics of the Au/SrTiO 3 /p-Si heterojunction structure was realized in the temperature range of 110-350 K (by step 30 K) at 1 MHz. The frequency-dependent reverse and forward bias C-V and G/ω−V characteristics of the Au/SrTiO 3 /p-Si heterojunction structure was realized in the frequency range of 100-900 kHz (by step 100 kHz) at room temperature. It has been demonstrated that Au/SrTiO 3 /p-Si heterojunction structure exhibits negative capacitance (NC) behavior as a result of both temperature-and frequency-dependent capacitance measurements due to the reduction of interface charges, ionization states and series resistance in the forward bias voltage. In addition, it was shown that it exhibits an intersection point in the forward bias voltage of both temperature and frequencydependent capacitance measurements. In temperature and frequency-dependent admittance spectroscopy measurements of Au/SrTiO 3 /p-Si heterojunction structure was observed NC phenomenon.

Silicon, 2020

The TiO 2 /SiO 2 film being the dielectric layer was grown on the n-Si wafer using radio frequenc... more The TiO 2 /SiO 2 film being the dielectric layer was grown on the n-Si wafer using radio frequency (RF) magnetron sputtering. Thus, the Au/TiO 2 /SiO 2 /n-Si metal-oxide-semiconductor (MOS) capacitor was fabricated with the forming of metal contacts. The optical properties of the oxide film were analyzed by Fourier transform infrared (FTIR) and Ultraviolet-visible (UV-Vis) spectroscopy. The electrical properties of the MOS capacitor were investigated using admittance (Y = G + iωC) measurements performed at various frequencies. The series resistance (R s) parameter of the capacitor was derived from the conductance method.

Current Applied Physics, 2018

Mo films deposited by DC sputtering are widely used as back contact in CIGS and CZTS based thin f... more Mo films deposited by DC sputtering are widely used as back contact in CIGS and CZTS based thin film solar cells. However, there have been only a few studies on the deposition of Mo films by RF sputtering method. In this context, Mo films on SLG substrates were prepared as a function of deposition pressure and power by using RF magnetron sputtering method to contribute to this shortcoming. Mo films were deposited at 250 C substrate temperature by using 20, 15, 10 mTorr Ar pressures at 120 W RF power and 10 mTorr Ar pressure at 100 W RF power. Structural, morphological and reflectivity properties of RFsputtered Mo films were clarified by XRD, AFM, FE-SEM and UVeVis measurements. In addition, due to sodium incorporation from SLG substrate to the absorber layer through Mo back contact layer is so essential in terms of improving the conversion efficiency values of CIGS and CZTS thin film solar cell devices, the effects of Na diffusion in the films were analyzed with SIMS depth profile. The electrical properties of the films such as mobility, carrier density and resistivity were determined by Hall Effect measurements. It was found that Mo films prepared at 120 W, 10 mtorr and 250 C substrate temperature and then annealed at 500 C for 30 min, had resistivity as low as 10 À5 U cm, as well as higher amount of Na incorporation than other films.

Journal of Electronic Materials, 2016

Two AlInN/AlN/GaN heterostructures with 280-nm-and 400-nm-thick AlN buffer grown on sapphire subs... more Two AlInN/AlN/GaN heterostructures with 280-nm-and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (10 12) plane in the 280nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (10 12) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 9 10 8 cm À2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.

In this work, the hot-electron transport properties of AlInN/AlN/GaN HEMT structures with a high ... more In this work, the hot-electron transport properties of AlInN/AlN/GaN HEMT structures with a high sheet electron density of 4.84×10 13 cm −2 grown by MOCVD (Metal Organic Chemical Vapor Deposition) on sapphire substrate were investigated at lattice temperature ranging from 10 K to 300 K. High speed current-voltage measurements and Hall measurements were used to study hot-electron transport. Current-voltage characteristics show that current and drift velocity increase linearly but deviate from the linearity towards high voltages, as would be expected from the increased scattering of hot electrons with LO phonons. However, no saturation of current and drift velocity were observed at the highest voltage reached. Drift velocities were deduced as approximately 6.7×10 6 and 6.1×10 6 cm/s at an electric field of around E ~ 23 kV/cm at lattice temperatures TL = 10 K and 300 K, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, the so-called mobility comparison method with power balance equations were used. The effect of hot-phonon production on the phonon lifetime and effective energy relaxation of hot electrons was investigated as a function of lattice temperature.

Journal of Materials Science: Materials in Electronics, 2012

The structural, optical and morphological properties of Ga-rich Ga x In 1-x P layers with various... more The structural, optical and morphological properties of Ga-rich Ga x In 1-x P layers with various gallium compositions grown on epi-ready semi-insulating (100)-oriented GaAs substrates by using Molecular Beam Epitaxy technique are presented in this study. The Ga x In 1-x P/GaAs structures (S1, S2 and S3) have been evaluated by means of high resolution X-ray diffraction, photoluminescence (PL) and atomic force microscopy measurements at room temperature. Experimental forward and reverse bias current-voltage (I-V) characteristics of structure S3 was investigated at room temperature due to its better characteristics when compared to the other two samples. The main electrical parameters such as ideality factor (n), barrier height (U b) and series resistance (R s) were extracted from forward bias I-V characteristics and Cheung's function. In addition, Hall measurements were carried out as a function of temperature (30-300 K) and at a magnetic field of 0.4 T were presented for structure S3.