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Öğe A comparison study regarding Al/p-Si and Al/(carbon nanofiber-PVP)/p-Si diodes: current/impedance-voltage (I/Z-V) characteristics(Springer Heidelberg, 2020) Sevgili, Omer; Yildirim, Mert; Azizian-Kalandaragh, Yashar; Altindal, SemsettinAl/p-Si and Al/(carbon nanofiber-PVP)/p-Si diodes were produced using a p-type silicon wafer with 10 omega cm resistivity to determine the polymer interlayer effects on device characteristics. To assess whether carbon nanofiber-PVP interlayer is beneficial for electrical performance, the current-voltage (I-V) and the impedance-voltage (Z-V) measurements were performed in wide range of voltage. Thus, electrical parameters such as series resistance, barrier height, and ideality factor were derived from the forward bias Ln (I-F)-V(F)and Cheung's functions, so that they are compared and voltage dependence of them is explored. Later, the values of intercept voltage, width of depletion layer, doping acceptor atom concentration, and barrier height were also extracted from C-2-Vdata at 1 MHz and then results were compared with each other. The surface states and their energy profile were also extracted from theI(F)-V(F)characteristics by considering barrier height (BH) and n is voltage dependent as well. Experimental results indicate that the carbon nanofiber-PVP interlayer decreases surface states (N-ss), series resistance (R-s) and leakage current, whereas it increases rectifying ratio and shunt resistance. Hence, such polymeric interlayer material forms an interesting alternative to conventional oxide layer due to some advantages of polymers such as desirably low values of cost, weight, and energy consumption.Öğe Distribution of interface traps in Au/2% GC-doped Ca3Co4Ga0.001Ox/n-Si structures(Wiley, 2020) Eroglu, Ayse Gul; Yildirim, Mert; Durmus, Perihan; Dokme, IbilgeThis study presents voltage-dependent profile of interface traps in Au/n-Si structure with 2% graphene-cobalt-doped Ca3Co4Ga0.001Ox interfacial layer. Admittance measurements revealed capacitance-voltage (C-V) plots with typical regions of a metal-insulator-semiconductor structure through inversion, depletion, and accumulation regions. Frequency dispersion is observed in C-V plots and such behavior was explained with excess capacitance, which is associated with the density of interface traps (D-it) in the structure because larger D-it is observed when the measurements are held at low frequencies due to the fact that traps can follow the signal depending on their lifetime. D-it was also obtained using conductance method, which also provided lifetime of the traps. The difference between the values of D-it was attributed to the difference in extraction methods. Obtained results showed that Au/2% graphene-cobalt-doped Ca3Co4Ga0.001Ox/n-Si structure yields promising electrical characteristics when the structure is operated at high frequencies. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48399.Öğe Effect of intermolecular charge transfer between Ni(II)Pc and CdSeS/ZnS QD on dielectric relaxation mechanism of 5CB nematic liquid crystals in the presence of UV illumination(Springer, 2020) Kocakulah, Gulsum; Yildirim, Mert; Koysal, OguzThis paper is a report on electro-optical and dielectric parameters of Ni(II)Pc (nickel(II) phthalocyanine) and CdSeS/ZnS (cadmium selenide sulfide/zinc sulfide) quantum dot (QD) doped 5CB (4-pentyl-4 '-cyanobiphenyl) nematic liquid crystal (LC) in the dark and under UV illumination condition. Electro-optical and dielectric measurements of the samples were carried out using electro-optical switching and dielectric spectroscopy methods, respectively. Dielectric anisotropy, relaxation frequency, dielectric strength, and threshold voltage values were determined using the experimental data. Investigation of dielectric properties demonstrates that relaxation frequency is decreased because of the dispersal of Ni(II)Pc and CdSeS/ZnS QD under UV exposure. The electro-optical investigation also shows that UV illumination and dispersal of Ni(II)Pc and CdSeS/ZnS QD cause a decrease in threshold voltages. Overall, results indicate that Ni(II)Pc, CdSeS/ZnS QD and UV light enhanced the electro-optical and dielectric properties of 5CB nematic LC.Öğe Influence of UV light intensity on dielectric behaviours of pure and dye-doped cholesteric liquid crystals(Springer, 2020) Kocakulah, Gulsum; Yildirim, Mert; Koysal, Oguz; Ercan, IsmailThis study aims to explore the ultraviolet (UV) light effects on dielectric properties of azo dye methyl red (MR)-doped cholesteric liquid crystal (CLC) composite. The CLC composite formed in the study contains 5CB nematic liquid crystal (LC) and S811 chiral additive. To obtain CLC/MR composite, CLC was dispersed with 2% wt/wt MR azo dye. Dielectric measurements of the CLC and CLC/MR samples were performed using dielectric spectroscopy technique in wide frequency range in the absence of UV light and at various UV light intensities (30, 60 and 90 mW/cm(2)) for 0 and 40 V. It was observed that the dielectric constant increased with UV light at low-frequency values. Dielectric loss data were utilized to extract relaxation frequency which was observed to increase with UV light exposure. Dielectric anisotropy of CLC sample exhibited typical transition from p-type to n-type, but this behaviour disappears for CLC/MR composite above 60 mW/cm(2) UV light intensity. Cole-Cole plots were used for extraction of dielectric relaxation data and obtained results showed that CLC sample shows Debye type relaxation only at 0 V whereas CLC/MR composite exhibits non-Debye type relaxation both at 0 V and 40 V. Moreover, conductivity properties of the samples were also investigated, and dc conductivity values were extracted from experimental ac conductivity values. It was found that MR incorporation increased dc conductivity, also it was significantly increased by UV light exposure and thus similar effect was also observed in current-voltage characteristics of the samples. The results show that azo dye MR molecules are suitable for CLCs since they lead to some enhancements in dielectric and electrical properties.Öğe One-step preparation of poly(NIPAM-pyrrole) electroconductive composite hydrogel and its dielectric properties(Wiley, 2021) Sarkaya, Koray; Yildirim, Mert; Alli, AbdulkadirConductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one-step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N-isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N-methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)-pyrrole) electroconductive composite hydrogel was 9.88 g of H2O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM-PPy) conductive hydrogel (700 degrees C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600 degrees C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM-PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non-Debye relaxation since experimental data fit into dielectric model of Havriliak-Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 x 10(-11) and 1.02 x 10(-8) S/cm, respectively. Real part of impedance at low frequencies also points out similar to 10(3) times lower resistance values at 10 Hz for composite poly(NIPAM-PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.Öğe The origin of anomalous peak and negative capacitance in the forward bias C-V characteristics of Au/n-GaAs contacts at low temperatures (T <= 300 K)(Natl Inst Optoelectronics, 2020) Dokme, Ilbilge; Yeriskin, Seckin Altindal; Yildirim, Mert; Durmus, PerihanAu/n-GaAs contacts were fabricated using n-GaAs wafer with high doping concentration and their electrical characteristics were investigated via admittance measurements at low temperatures (T <= 300 K) at 1MHz. The main electronic parameters such as barrier height, depletion region width, doping concentration, series resistance and Fermi energy were obtained from experimental data. All these parameters showed dependence on temperature since different conduction mechanisms may play role at a certain voltage and temperature range. The forward bias capacitance-voltage curve exhibited an anomalous peak and then capacitance took negative values for each temperature. Such negative capacitance behaviour can be explained by the loss of interface charges located at junction, the existence of surface states, series resistance and a native interlayer. The decrease in series resistance and increase in surface states with increasing temperature were attributed to the decrease in band gap of GaAs and restructuring and reordering of surface charges.
