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Evaluation of novel thiophene branched polystyrene as insulator layer in organic electronic device
(Elsevier Science Bv, 2019) Günaydın, Okan; Demir, Ahmet; Atahan, Alparslan; Yardım, Tayfun; Yücedağ, İbrahim
A novel thiophene branched polystyrene copolymer (PS-Th) was successfully synthesized and well characterized. Two different Organic Field Effect Transistor (OFET) devices were fabricated by using this novel PS-Th material and polystyrene (PS) as insulator materials and main performance parameters of the devices such as mobility (mu(FET)), on/off ratio (I-on/off), and threshold voltage (V-Th) were compared. Consequently, our results indicated that PS-Th copolymer was efficiently working as dielectric material for OFETs. Moreover, mu(FET) significantly enhanced (approx. 3.7 times) compared to the PS based OFET device while V-Th and I-on/off were slightly increasing. This situation can be explained by well organized molecular arrangement at the dielectric-semiconductor interface via thiophene-thiophene interaction between semiconductor material Poly(3-hexylthiophene-2,5-diyl) (P3HT) and insulator material PS-Th chains. (C) 2019 Elsevier B.V. All rights reserved.
Enhancement of electro-optical and dielectric properties of CdSeS/ZnS semiconductor quantum-dot-doped nematic liquid crystals in the presence of UV-illumination effect
(Springer Heidelberg, 2019) Kocakülah, Gülsüm; Köysal, Oğuz
In this study, we have investigated ultraviolet (UV) illumination effect on electro-optical and dielectric properties of varying concentration of CdSeS/ZnS semiconductor quantum-dot-doped 5CB nematic liquid crystal. Dielectric measurements were made from 10kHz to 10MHz frequency ranges in dark and under UV-illumination conditions. Electro-optical measurements were also performed with a voltage-dependence light transmission system at 10kHz frequency in dark and under UV-illumination conditions. Significant physical parameters such as relaxation frequency (f(R)), real and imaginary components of complex dielectric permittivity (epsilon and epsilon), and threshold voltage (V-th) values were obtained from experimental results. Results show that UV-illumination effects cause considerable improvements on electro-optical and dielectric characteristic of investigated samples.
Enhancement of Dielectric Characteristics of Polyvinyl Alcohol (PVA) Interfacial Layer in Au/PVA/n-Si Structures by Bi2O3 Disperse
(Wiley, 2013) Gökçen, Muharrem; Tunç, Tuncay
Dielectric characteristics such as dielectric constant (epsilon), dielectric loss (epsilon), dielectric loss tangent (tan) and real and imaginary parts of electrical modulus (M and M), and ac electrical conductivity (sigma(ac)) of Au/ Polyvinyl Alcohol (PVA) (Bi2O3-dispersed)/n-Si structures have been investigated by using admittance measurements. Results show that the epsilon values of Au/PVA/n-Si with Bi2O3-dispersed PVA interfacial layer are very higher compared with those with pure and other dopant/mixture's of PVA. Thus, PVA is made very compatible for device applications with the enhanced dielectric properties by Bi2O3 disperse and its native very high dielectric strength.
Electro-optical and dielectric performance analysis: the influence of azo dye on polymer/LC composite structures
(Springer Heidelberg, 2019) Kocakülah, Gülsüm; Önsal, Gülnur; Köysal, Oğuz
In the present work, electro-optical and dielectric properties of polymer/LC doped with azo dye methyl red (MR) were investigated. Norland optical adhesive (NOA65) and nematic liquid-crystal (E63-coded nematic liquid crystal) materials were used to compose of polymer/LC composite structure. A doping agent ratio of MR was chosen 1% wt/wt in polymer/LC composite structure. Dielectric measurements of the obtained samples were held between 10Hz and 10MHz at room temperature using dielectric/impedance analyzer. Physical parameters such as dielectric permittivity, dielectric anisotropy, electric modulus, loss tangent, relaxation frequency, relaxation time, threshold voltage, and splay elastic constant were obtained from experimental data. Optical bandgap values of polymer/LC and polymer/LC/MR composite structures were estimated using UV spectroscopy technique. Polymer/LC composite structures' electro-optical properties were affected the MR dispersal which was reduced the anchoring force between polymer and LC molecules; therefore, threshold voltage and splay elastic constant decreased. In addition, dispersal of MR caused a decrease in optical bandgap values of polymer/LC composite structures. Due to the increase in charge density caused by MR, the value of the current passing through the polymer/LC composite structures increased as well as its dependence on voltage. Results show that MR dispersal enhanced electro-optical and dielectric properties of polymer/LC composite structures and makes it suitable to design new based on optoelectronic device applications.
High work-function hole transport layers by self-assembly using a fluorinated additive
(Royal Soc Chemistry, 2014) Mauger, Scott A.; Li, Jun; Özmen, Özge Tüzün; Yang, Andy Y.; Friedrich, Stephan; Rail, M. Diego; Moule, Adam J.
The hole transport polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) derives many of its favorable properties from a PSS-rich interfacial layer that forms spontaneously during coating. Since PEDOT: PSS is only usable as a blend it is not possible to study PEDOT: PSS without this interfacial layer. Through the use of the self-doped polymer sulfonated poly(thiophene-3-[2-(2-methoxyethoxy) ethoxy]-2,5-diyl) (S-P3MEET) and a polyfluorinated ionomer (PFI) it is possible to compare transparent conducting organic films with and without interfacial layers and to understand their function. Using neutron reflectometry, we show that PFI preferentially segregates at the top surface of the film during coating and forms a thermally-stable surface layer. Because of this distribution we find that even small amounts of PFI increase the electron work function of the hole transport layer. We also find that annealing at 150 degrees C and above reduces the work function compared to samples heated at lower temperatures. Using near edge X-ray absorption fine structure spectroscopy and gas chromatography we show that this reduction in work function is due to S-P3MEET being doped by PFI. Organic photovoltaic devices with S-P3MEET/PFI hole transport layers yield higher power conversion efficiency than devices with pure S-P3MEET or PEDOT: PSS hole transport layers. Additionally, devices with a doped interface layer of S-P3MEET/PFI show superior performance to those with un-doped S-P3MEET.
Gaussian distribution of inhomogeneous barrier height in Au/n-Si (111) Schottky barrier diodes at low temperatures
(Elsevier Sci Ltd, 2014) Durmuş, Perihan; Yıldırım, Mert
Forward bias current-voltage (I-V) characteristics of Au/n-Si (111) Schottky barrier diode (SBD) were investigated in the temperature range of 80-290 K. Analysis of temperature dependent I-V data in terms of thermionic emission (TE) theory revealed an abnormal increase in zero-bias barrier height (Phi(B0)) and decrease in ideality factor (n) with increasing temperature. Such behavior of Phi(B0) and n was attributed to barrier inhomogeneities by assuming a Gaussian distribution (GD) of barrier height. Therefore, mean barrier height and effective Richardson constant (A*) values were extracted from the modified Richardson plot, and extracted A* was found close to the theoretical value for n-type Si. Hence, it has been concluded that temperature dependent I-V characteristics of the SBD can be successfully explained on the basis of TE theory with GD of barrier height. In addition, series resistance and energy profile of density of interface traps in the SBD were also investigated. (C) 2014 Elsevier Ltd. All rights reserved.
Frequency Dependent Electrical and Dielectric Properties of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky Barrier Diode
(Springer, 2017) Taşçıoğlu, İlke; Özmen, Özge Tüzün; Şağban, Muzaffer; Yağlıoğlu, E.; Altındal, Ş.
In this study, poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (P3HT:PCBM:F4-TCNQ) organic film was deposited on n-type silicon (n-Si) substrate by spin coating method. The electrical and dielectric analysis of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky barrier diode was conducted by means of capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements in the frequency range of 10 kHz-2 MHz. The C-V-f plots exhibit fairly large frequency dispersion due to excess capacitance caused by the presence of interface states (N (ss)). The values of N (ss) located in semiconductor bandgap at the organic film/semiconductor interface were calculated by Hill-Coleman method. Experimental results show that dielectric constant (epsilon') and dielectric loss (epsilon aEuro(3)) decrease with increasing frequency, whereas loss tangent (tan delta) remains nearly the same. The decrease in epsilon' and epsilon aEuro(3) was interpreted by the theory of dielectric relaxation due to interfacial polarization. It is also observed that ac electrical conductivity (sigma (ac)) and electric modulus (M' and MaEuro(3)) increase with increasing frequency.
Frequency and voltage dependence of negative capacitance in Au/SiO2/n-GaAs structures
(Elsevier Sci Ltd, 2012) Gökçen, Muharrem; Altuntaş, Havva; Altındal, Şemsettin; Özçelik, Süleyman
The frequency (f) and bias voltage (V) dependence of electrical and dielectric properties of Au/SiO2/n-GaAs structures have been investigated in the frequency range of 10 kHz-3 MHz at room temperature by considering the presence of series resistance (R-s). The values of R-s, dielectric constant (epsilon'), dielectric loss (epsilon '') and dielectric loss tangent (tan delta) of these structures were obtained from capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements and these parameters were found to be strong functions of frequency and bias voltage. In the forward bias region, C-V plots show a negative capacitance (NC) behavior, hence epsilon'-V plots or each frequency value take negative values as well. Such negative values of C correspond to the maximum of the conductance (G/omega). The crosssection of the C-V plots appears as an abnormality when compared to the conventional behavior of ideal Schottky barrier diode (SBD), metal-insulator-semiconductor (MIS) and metal-oxide-semiconductor (MOS) structures. Such behavior of C and epsilon' has been explained with the minority-carrier injection and relaxation theory. Experimental results show that the dielectric properties of these structures are quite sensitive to frequency and applied bias voltage especially at low frequencies because of continuous density distribution of interface states and their relaxation time. (c) 2011 Elsevier Ltd. All rights reserved.
Forward and reverse bias current-voltage characteristics of Au/n-Si Schottky barrier diodes with and without SnO2 insulator layer
(Elsevier, 2011) Gökçen, Muharrem; Altındal, Şemsettin; Karaman, Mehmet; Aydemir, Umut
The effects of interfacial insulator layer, interface states (N-ss) and series resistance (R-s) on the electrical characteristics of Au/n-Si structures have been investigated using forward and reverse bias current-voltage (I-V) characteristics at room temperature. Therefore, Au/n-Si Schottky barrier diodes (SBDs) were fabricated as SBDs with and without insulator SnO2 layer to explain the effect of insulator layer on main electrical parameters. The values of ideality factor (n), R-s and barrier height (Phi(Bo)) were calculated from ln(I) vs. V plots and Cheung methods. The energy density distribution profile of the interface states was obtained from the forward bias I-V data by taking bias dependence of ideality factor, effective barrier height (Phi(e)) and R-s into account for MS and MIS SBDs. It was found that N-ss values increase from at about mid-gap energy of Si to bottom of conductance band edge of both SBDs and the MIS SBD's N-ss values are 5-10 times lower than those of MS SBD's. An apparent exponential increase from the mid-gap towards the bottom of conductance band is observed for both SBDs' (MS and MIS) interface states obtained without taking R-s into account. (C) 2011 Elsevier B.V. All rights reserved.
Ferromagnetic resonance in double perovskite epitaxial thin films of La2NiMnO6 on SrTiO3 and NdGaO3 substrates
(Amer Inst Physics, 2010) Kazan, Sinan; Mikailzade, F.A.; Özdemir, Mustafa; Aktaş, Bekir; Rameev, Bulat; İntepe, A.; Gupta, Amit
Ferromagnetic resonance (FMR) studies of epitaxial La2NiMnO6 (LNMO) thin films on (100) oriented SrTiO3 and (110) oriented NdGaO3 substrates at room temperature are presented. Observation of FMR spectra above the Curie temperature of this compound confirms the presence of magnetic ordering in LNMO thin films at room temperature. Best fitting of FMR spectra has been made on the assumption of the coexistence of two magnetic phases with different easy and hard axis periodicities in the film plane of LNMO. The spectra of the films on various substrates are characterized by different in-plane and out-of-plane symmetries, which indicates the existence of different epitaxial growth on the substrates with different crystal symmetries and orientations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3481678]
F4-TCNQ concentration dependence of the current-voltage characteristics in the Au/P3HT:PCBM:F4-TCNQ/n-Si (MPS) Schottky barrier diode
(Iop Publishing Ltd, 2014) Yağlıoğlu, E.; Özmen, Özge Tüzün
In this study, we investigate some main electrical parameters of the gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester:2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane/n-type silicon (Au/P3HT:PCBM:F4-TCNQ/nSi) metal-polymer-semiconductor (MPS) Schottky barrier diode (SBD) in terms of the effects of F4-TCNQ concentration (0%, 1%, and 2%). F4-TCNQ-doped P3HT:PCBM is fabricated to figure out the p-type doping effect on the device performance. The main electrical parameters, such as ideality factor (n), barrier height (Phi(B0)), series resistance (R-s), shunt resistance (R-sh), and density of interface states (N-ss) are determined from the forward and reverse bias current-voltage (I-V) characteristics in the dark and at room temperature. The values of n, R-s, Phi(B0), and N-ss are significantly reduced by using the 1% F4-TCNQ doping in P3HT:PCBM:F4-TCNQ organic blend layer, additionally, the carrier mobility and current are increased by the soft (1%) doping. The most ideal values of electrical parameters are obtained for 1% F4-TCNQ used diode. On the other hand, the carrier mobility and current for the hard doping (2%) become far away from the ideal diode values due to the unbalanced generation of holes/electrons and doping-induced disproportion when compared with 1% F4-TCNQ doping. These results show that the electrical properties of MPS SBDs strongly depend on the F4-TCNQ doping and doping concentration of interfacial P3HT:PCBM:F4-TCNQ organic layer. Moreover, the soft F4-TCNQ doping concentration (1%) in P3HT:PCBM:F4-TCNQ organic layer significantly improves the electrical characteristics of the Au/P3HT:PCBM:F4-TCNQ/n-Si (MPS) SBDs which enables the fabricating of high-quality electronic and optoelectronic devices.
Electrical characterization of Au/poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA)/n-Si diode in dark and under illumination
(Elsevier Science Bv, 2015) Yasan, M.; Gökçen, Muharrem; Allı, Abdulkadir; Allı, Sema
In this study, poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA) graft copolymer is used as an interfacial layer in a Schottky diode for the first time. Au/poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA)/n-Si diode was fabricated and main electrical characteristics of the diode were investigated using I-V measurements in dark and under illumination at room temperature. Ideality factor (n), barrier height (Phi(B0)) and serial resistance (R-s) values of the diode were found as 2.8, 0.87 eV and 8096 Omega for dark, and 6.3, 0.71 eV and 676 Omega for 100 mW/cm(2) illumination intensity. Also, the reasons of deviation from ideal thermionic emission theory were investigated using Cheung&Cheung method and Card&Rhoderick's function which are used for calculating voltage dependence of barrier height (Phi(B)(V)), series resistance (R-s) and number of surface states (N-ss) of the Au/PLiMMA/n-Si diode. (C) 2014 Elsevier B.V. All rights reserved.
Electrical and photocurrent characteristics of Au/PVA (Co-doped)/n-Si photoconductive diodes
(Elsevier, 2012) Gökçen, Muharrem; Tunç, Tuncay; Altındal, Şemsettin; Uslu, İbrahim
In this work, we investigate the some main electrical and photocurrent properties of the Au/PVA(Co-doped)/n-Si diodes by using current-voltage (I-V) measurements at dark and various illumination intensity. Two types of diodes with and without polyvinyl alcohol (PVA) (Co-doped) polymeric interfacial layer were fabricated and measured at room temperature. Results show that the polymeric interfacial layers and series resistance (R-s) strongly affect the main electrical parameters of these structures. Also, metal/polymer/semiconductor (MPS) diode with PVA (Co-doped) interfacial organic layer is very sensitive to the light such that the current in reverse bias region increase by 10(3)-10(4) times with the increasing illumination intensity. The open circuit voltage V-oc and short-circuit current I-sc values of this MPS diode under 100 mW/cm(2) illumination intensity were found as 0.28 V and 19.3 mu A, respectively. (C) 2012 Elsevier B.V. All rights reserved.
Electrical and interfacial properties of Au/P3HT:PCBM/n-Si Schottky barrier diodes at room temperature
(Elsevier Sci Ltd, 2014) Özmen, Özge Tüzün; Yağlıoğlu, E.
In this study, a gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/n-type silicon (Au/P3HT:PCBM/n-Si) metal-polymer-semiconductor (MPS) Schottky barrier diode (SBD) was fabricated. To accomplish this, a spin-coating system and a thermal evaporation were used for preparation of a P3HT/PCBM layer system and for deposition of metal contacts, respectively. The forward- and reverse-bias current-voltage (I-V) characteristics of the MPS SBD at room temperature were studied to investigate its main electrical parameters such as ideality factor (n), barrier height (phi(B)), series resistance (R-s), shunt resistance (R-sh), and density of interface states (N-ss). The I-V characteristics have nonlinear behavior due to the effect of R-s, resulting in an n value (3.09) larger than unity. Additionally, it was found that n, phi(B), R-s, R-sh, and N-ss have strong correlation with the applied bias. All results suggest that the P3HT/PCBM interfacial organic layer affects the Au/P3HT:PCBM/n-Si MPS SBD, and that R-s and N-ss are the main electrical parameters that affect the Au/P3HT:PCBM/n-Si MPS SBD. Furthermore, a lower N-ss compared with that of other types of MPS SBDs in the literature was achieved by using the P3HT/PCBM layer. This lowering shows that high-quality electronic and optoelectronic devices may be fabricated by using the Au/P3HT:PCBM/n-Si MPS SBD. (C) 2014 Elsevier Ltd. All rights reserved.
Effects of PCBM concentration on the electrical properties of the Au/P3HT:PCBM/n-Si (MPS) Schottky barrier diodes
(Pergamon-Elsevier Science Ltd, 2014) Özmen, Özge Tüzün
In this study, the gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/n-type silicon (Au/P3HT:PCBM/n-Si) metal-polymer-semiconductor (MPS) Schottky barrier diodes (SBDs) were investigated in terms of the effects of PCBM concentration on the electrical parameters. The forward and reverse bias current-voltage (I-V) characteristics of the Au/P3HT:PCBM/n-Si MPS SBDs fabricated by using the different P3HT:PCBM mass ratios were studied in the dark, at room temperature. The main electrical parameters, such as ideality factor (n), barrier height (Phi(B0)), series resistance (R-s), shunt resistance (R-sh), and density of interface states (N-ss) were determined from I-V characteristics for the different P3HT:PCBM mass ratios (2:1, 6:1 and 10:1) used diodes. The values of n, R-s, Phi(B0), and N-SS were reduced, while the carrier mobility and current were increased, by increasing the PCBM concentration in the P3HT:PCBM organic blend layer. The ideal values of electrical parameters were obtained for 2:1 P3HT:PCBM mass ratio used diode. This shows that the electrical properties of MPS diodes strongly depend on the PCBM concentration of the P3HT:PCBM organic layer. Moreover, increasing the PCBM concentration in P3HT:PCBM organic blend layer improves the quality of the Au/P3HT:PCBM/n-Si (MPS) SBDs which enables the fabrication of high-quality electronic and optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.
Effects of glass substrate coated by different-content buffer layer on the quality of poly-Si thin films
(Wiley-V C H Verlag Gmbh, 2016) Karaman, Mehmet; Özmen, Özge Tüzün; Sedani, Salar Habibpur; Özkol, Engin; Turan, Raşit
In this work, polycrystalline silicon (poly-Si) thin films were fabricated by aluminum induced crystallization (AIC) technique. SiNx, deposited as a function of NH3/SiH4 ratio, and AZO (Al-doped ZnO) films on glass were used as a buffer layer between glass and Si film. The effect of buffer layer content on the crystallinity of poly-Si thin films was studied by Raman analysis which shows that fully crystallization without stress was achieved for all samples. Moreover, the preferred crystalline orientation and crystallite size of films were deduced by X-ray diffraction (XRD) analysis. The preferred orientation is <100> as independent from the buffer layer content while the crystallite sizes increase up to 48.5 nm by increasing the amount of SiH4. The electrical properties of the films were carried out by four point probe and currentvoltage (I-V) analysis. Both techniques demonstrated that the resistivity of the SiNx-based samples is around 0.1Ocm. The grain size analysis was accomplished by electron back scattering diffraction (EBSD) measurements. The grain size up to 25 mu m was achieved as observed from EBSD images. The results show that the fabrication parameters of SiNx and AZO buffer layers have the great effects on the crystallography of poly-Si films. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effect of multi wall carbon nanotube on electrical properties 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid liquid crystal host
(Elsevier Sci Ltd, 2015) Denktaş, Cenk; Ocak, Hale; Okutan, M.; Yıldız, Alptekin; Eran, Belkız Bilgin; Köysal, Oğuz
Dielectric properties, conductivity mechanisms and current voltage characteristics of Multi Wall Carbon Nanotube (MWCNT) doped and pure Liquid Crystal (LC) material was investigated using impedance spectroscopy method in the frequency range of 100 Hz to 15 MHz. Liquid crystalline material, 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid (CBBA) as a host material and MWCNT was used as doping material in this study. In order to observe the effects of doping MWCNT into LC on dielectric properties, an MWCNT material was doped into CBBA structure with 1 wt%. Real part of dielectric constants (epsilon'), imaginary part of dielectric constant (epsilon ''), i.e. dielectric loss, dissipation factor/dielectric loss tangent (tan delta) were obtained for the pure and doped LC samples. In addition, dielectric strength (bads), negative dielectric anisotropy (Delta epsilon da), absorption coefficients (alpha) and relaxation times (tau) were calculated from the empirical data. I-V characteristics of pure LC and doped LC structures were carried out at micro-current levels by current-voltage measurements. (C) 2015 Elsevier Ltd. All rights reserved.
Effect of frequency on dielectric properties of liquid crystal doped with side-chain liquid crystalline polymer
(Elsevier Science Sa, 2011) Gökçen, Muharrem; Köysal, Oğuz
The frequency and applied bias voltage dependence of the dielectric properties and dielectric anisotropy of liquid crystal (LC) doped with side-chain liquid crystalline polymer (SLCP) mixture have been investigated using the admittance spectroscopy method (C-V and G/omega-V) in the frequency range of 10 kHz to 10 MHz at room temperature. The liquid crystal used in this experiment is E63. The doping material used in this study is SLCP and its concentration is ensured 1 wt % in E63. Dielectric constant (epsilon'), dielectric loss (epsilon), dielectric loss tangent (tan delta) and real and imaginary parts of electrical modulus (M' and M '') of the E63/SLCP mixture was also calculated. Moreover, dielectric anisotropy (Delta epsilon) as a function of frequency was obtained. Results show that the values of the all dielectric parameters are strong functions of frequency and applied bias voltage. After a critical frequency, dielectric anisotropy has negative values according to p/n type changing. (C) 2011 Elsevier B.V. All rights reserved.
Double parallel barrier height behavior of Au/Poly (linoleic acid)-g-poly (methyl methacrylate) (PLiMMA)/n-Si structure
(Pergamon-Elsevier Science Ltd, 2019) Gökçen, Muharrem; Taran, Songül
The main electrical parameters and current conduction mechanisms of Au/Poly (linoleic acid)-g-poly (methyl methacrylate)/n-Si diode were carried out in the range of 300 K-400 K with a temperature increment of 10 K. Two distinct linear regions were observed in semi-logarithmic current-voltage (I-V) plots for each investigated temperature. For each linear region, leakage currents, barrier heights and ideality factors which are main electrical parameters of the diode were extracted from the experimental I-V measurements. Also, interface state density was derived by Card and Rhoderick's function. To obtain effective current conduction mechanisms, lnI versus lnV plots were obtained by taking into account of double linear region of current-voltage plots and abnormal increasing of barrier height and ideality factor at above the room temperature.
Dielectric properties of CdSeS/ZnS quantum dots doped PMMA/LC composite structure
(Taylor & Francis Ltd, 2019) Kocakülah, Gülsüm; Önsal, Gülnur; Köysal, Oğuz
In this work, electrical and dielectric properties of CdSeS/ZnS quantum dots (QDs) doped Polymer/Liquid Crystal composite structures (PMMA/LC) were investigated by using Dielectric Spectroscopy Technique in the frequency range of 100 Hz-10 MHz at room temperature. In order to determine the effect of quantum dot concentrations, PMMA/LC composites structure was dispersed with 0.5, 1 and 1.5 wt% CdSeS/ZnS QDs. Hence some considerable physical parameters such as dielectric constant (epsilon ' and epsilon ''), dielectric anisotropy (Delta epsilon '), relaxation frequency (f(R)), relaxation time (tau) as a function of frequency were obtained depend on QDs concentrations. Results show that QDs contribution have occurred significant changes in dielectric properties of investigated samples which can be used in PMMA/LC based device applications.

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