Browsing by Author "Kurnaz S."

Now showing 1 - 7 of 7

A detailed research for determination of Er/Gd co-doping effect in ZnO-NPs thin films on optical, electrical and crystallographic properties
(2023-01-01) Asikuzun Tokeser E.; Ozturk O.; Kurnaz S.; Cicek C.; Seydioglu T.
Undoped, Er and Gd doped ZnO transparent semiconductor thin films were coated on non-alkaline glass using the sol–gel dip-coating method. Methanol and ethanolamine (MEA) were chosen as solvents and stabilizers. Er doping concentration was maintained at 5%. The effects of both different dopants and different dip numbers on the optical, electrical and structural properties of ZnO thin films were analyzed. According to the XRD patterns, hexagonal structure was seen in all films. The optical transmittance of impurity elements doped ZnO thin films increased with the increasing of Gd doping. High transparency was determined to doped films in the visible region. The electrical properties of the Er/Gd co-doped ZnO thin films were measured by Van der Pauw Hall measurements technique that determined the bulk carrier concentration, the Hall mobility and the resistivity at room temperature. Er and Gd doped films shown lower Hall mobility and resistivity than undoped ZnO thin films. In the bulk carrier concentration, it was seen that there was an increase in 5 dip and 10 dip, while it decreased in 20 dip.
Comparative investigation on electronic properties of metal-semiconductor structures with variable ZnO thin film thickness for sensor applications
(2019-10-01) Çiçek O.; Kurnaz S.; Bekar A.; Öztürk Ö.
In this work, AuPd/n-GaAs and Ag/n-GaAs metal–semiconductor structures, which is known as Schottky Junction Structures (SJSs), with various ZnO thin film thickness (25–250 nm) classified as Group AuPd and Group Ag were produced to investigate electronic properties on SJSs. The current-voltage (I–V) characteristics of SJSs operating in their forward and reverse regions operating at ±3 V were measured at room temperature (295 K). The electronics parameters such as the series resistance (Rs), the shunt resistance (Rsh), the ideality factor (n) and the barrier height (ΦB0) were calculated by using thermionic emission (TE) theory, Ohm's law, Cheung and Cheung's function and modified Norde's function. Labview® based characterization tool developed to calculate the electronic parameters. The results were compared according to the various thicknesses and different rectifier contacts. Experimentally, if the results are analysed for each group, a (gradual) decrease in ZnO thicknesses is caused by an increase in the values of n, ФB0, RR. In addition, the Rsh values were significantly increased while the Rs values were almost close to each other. As the ΦB0 values, while compatible with the values found in the Cheung and Cheung's function, they are slightly higher than the values found in the TE theory. On the other hand, due to the voltage-dependent barrier height and nature of the used method, ФB0 values from modified Norde's function are a little higher than the TE theory. Finally, it can be clearly seen that electronic parameters of SJSs based on sensor applications can be arranged with various thicknesses according to extracted results.
Comparison of the Dopant Effect and Sample Preparation Method on Y-123 Superconductors
(2021-11-01) Ozturk O.; Nefrow A.R.A.; Bulut F.; Kurnaz S.; Safran S.
The detailed comparison of the effects of Co and CoFe2O4 dopants and preparation methods (solid-state reaction method and sol–gel methods) have been studied on structural, electrical, superconducting, and mechanical properties of Y123 bulk superconductors. The doping amounts of Co and CoFe2O4 were chosen up to 0.10 wt. %. X-ray powder diffraction (XRD) method, temperature-dependent resistance measurement (R-T), and Vickers microhardness analyses were performed to characterize prepared samples. XRD analysis showed that all samples have Pmmm symmetry of orthorhombic crystal structure; intensities and width of the diffraction lines were affected by doping material, but, independent of the preparation method. Although all samples crystallize in orthorhombic structure and exhibit superconductivity behavior, with increasing doping rate the critical transition temperatures of the samples showed a significant decrease and broadened to superconducting temperature transition width. This is more evident in CoFe2O4-doped Y-123 samples produced by sol–gel method. As the applied force increased, it was observed that the microhardness values of the Co-doped samples increased while the CoFe2O4-doped samples decreased, regardless of the sample preparation method.
Flexible capacitive and piezoresistive pressure sensors based on screen-printed parylene C/polyurethane composites in low-pressure range
(2023) Kurnaz S.; Ozturk O.; Mehmet A.H.; Guduloglu U.; Yilmaz N.; Cicek O.
The use of polymers to fabricate flexible pressure sensors as an alternative to conventional pressure sensors has led to the development of physiological monitoring of human body and the electronic skin. In particular, the fabrication of flexible capacitive and piezoresistive sensors using a variety of materials and the investigation of their electromechanical properties are further developments in these fields. Herein, parylene C is synthesized via chemical vapor deposition method. Pressure-sensitive inks are prepared with a composite of parylene C, polyurethane, polymethylmethacrylate, and activated carbon at certain weight ratios. Flexible capacitive and piezoresistive pressure sensors are fabricated by the screen printing method. The sensitivity, detection limit, linearity range, and response/relaxation time, which define the capacitive and piezoresistive properties are investigated and presented in this paper. The sensitivities of the flexible capacitive and piezoresistive pressure sensors are 0.124 kPa−1 and 0.074 kPa−1 in the pressure range of 0.07-1.39 kPa. This study enables parylene C to be used in the composite structure and shows that it can be used not only as a protective layer but also in flexible pressure sensor applications. It also ensures that the design of the flexible capacitance pressure sensor can measure low pressure with high sensitivity compared to the flexible piezoresistive pressure sensor.
Self-powered visible-UV light photodiodes based on ZnO nanorods-silicon heterojunctions with surface modification and structural enhancement
(2022-07-01) Çiçek O.; Karasüleymanoğlu M.; Kurnaz S.; Öztürk Ö.; Taşçı A.T.
The letter reports the visible-UV light response of Al/ZnONRs/ZnOseed/p-Si/Al type photodiodes (PDs) with surface modification and structural enhancement. The PDs, which are referred to as PD10–2, PD10–4, PD20–2, PD20–3, and PD20–4 according to molar concentration (mM) and time (hour), were produced for improving the performances. Basic electronic parameters were obtained from the I-V data of Al/ZnONRs/ZnOseed/p-Si/Al type PDs by using thermionic emission (TE) theory, Ohm's law, and Cheung's methods. In accordance with the literature, the results showed that the potential barrier height (ФBo) values decreased with the increasing illumination intensity, while the ideality factor (n) values increased. In addition, voltage-dependent series resistance (Rs) values of the PDs under dark and different visible-UV light intensities were calculated by using Ohm's law and Cheung's method. It was observed that the Rs values decreased with increasing light intensities. On the other hand, the photosensitivity characteristics of the PDs at visible-UV light intensities were investigated depending on the applied voltage. While the photosensitivity value of the produced PD10–2 device reached the maximum value of 6.9 × 103 at the short-circuit voltage Vsc= 0 V, the open-circuit voltage Voc showed better photosensitivity with a minimum value of 0.0702 in the self-powered mode. In addition, the responsivity (R) and the detectivity (D*) values of Al/ZnONRs/ZnOseed/p-Si/Al type PDs were calculated. Herein, the R and D* values decreased with increasing power density at zero-bias voltage in accordance with the literature. Also, the R and D* values of the PD10–2 device are higher and lower than other devices, respectively. The linear dynamic range (LDR) value of the PD10–2 device reaches ~78 dB with a maximum value at Vbias= 0 V, while the dark current is 0.21 nA with a minimum value, self-powered mode. It is concluded that the PD10–2 device is suitable for photodiode applications in self-powered mode.
Solar light performances of n-ZnO nanorods/p-Si-based photodetectors under high illumination intensity
(2022-06-01) Ozturk O.; Candan B.M.; Kurnaz S.; Cicek O.; Tasci A.T.
We present ZnO nanorod/ZnO thin film structures synthesized at different molarities and growth times using a hydrothermal method, exhibiting uniquely solar sensing characteristics. ZnO thin film was deposited on p-Si(100) substrate by using RF sputter. ZnO nanorods with different molarities (10 and 20 mM) and growth times (2, 3, and 4 h) were fabricated at 90 °C by using the hydrothermal method on the n-ZnO/p-Si. The surface texture was also examined by scanning electron microscopy. The diameter of ZnO NRs was in the range of 62–119 nm. The current–time measurements were done under solar light illumination intensity (50 and 100 mW/cm2) and forward bias voltage (1, 5, and 10 V). Decay time (τd), rise time (τr), detectivity (D*), responsivity (R), and sensitivity (S) parameters were calculated. Samples produced at 2 h and 3 h in 10 mM solution performed best due to low τd, τr, and high D*, R, S. Especially, the S for the PD102 changed from 4.24 to 11.8, while it was in the range of 0.41–7.33 for the PD103. The R was 5.81 AW−1 in PD102 and 1.19 AW−1 in PD103. The D* was 109–1011 cmHz1/2/W in PD102 and 1010–1011 cmHz1/2/W in PD103 at ± 6 V.
The parylene C as a flexible substrate and passivation layer: A promising candidate for a piezoelectric, piezoresistive, and capacitive pressure sensor in low-pressure range
(2023-01-01) Kurnaz S.; Ozturk O.; Yilmaz N.; Cicek O.