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A comparative study regarding effects of interfacial ferroelectric Bi4Ti3O12 (BTO) layer on electrical characteristics of Au/n-Si structures
(Indian Acad Sciences, 2014) Yıldırım, Mert; Gökçen, Muharrem
Present study focuses on the effects of interfacial ferroelectric BTO layer on the electrical characteristics of Au/n-Si structures, hence Au/n-Si (MS) and Au/BTO/n-Si (MFS) structures were fabricated and admittance measurements (capacitance-voltage: C-V and conductance-voltage: G/omega-V) of both structures were conducted between 10 kHz and 1MHz at room temperature. Results showed that C-V and G/omega-V characteristics were affected not only by frequency but also through deposition of BTO layer. Some effects can be listed as sharper peaks in C-V plots, higher capacitance and conductance values. Structure's series resistance (R-s) also decreased due to BTO layer. Interface states (N-ss) profiles of the structures were obtained using Hill-Coleman and high-low frequency capacitance (C-HF-C-LF). Some of the main electrical parameters were extracted from C-2-V plots using depletion capacitance approach. Furthermore, current-voltage characteristics of MS and MFS structures were presented.
Controlling the electrical characteristics of Au/n-Si structures by interfacial insulator layer
(Elsevier Sci Ltd, 2012) Yıldırım, Mert; Gökçen, Muharrem
Admittance (C-V and G/omega-V) measurements of Au/n-Si (metal-semiconductor, MS) and Au/SnO2/n-Si (metal-insulator-semiconductor, MIS) structures were carried out between 1 kHz and 1 MHz at room temperature to investigate the interfacial insulator layer effect on the electrical characteristics of Au/n-Si structures. Experimental results showed that MIS structure's capacitance (C) values, unlike those of MS structure, became stable especially at high frequencies in the accumulation region. Also, the insulator layer caused structure's shunt resistance (R-sh) to increase. It was found that series resistance (R-s) is more effective in the accumulation region at high frequencies after the correction was applied to C and G/omega) data to eliminate the R-s effect. The density of interface states (D-is) was obtained using Hill-Coleman method, D-is values MIS structure was obtained smaller than those of MS structure. Results indicate that interfacial insulator layer brings about some improvements in electrical characteristics of Au/n-Si structures. (C) 2012 Elsevier Ltd. All rights reserved.
Current conduction in Schottky barrier diodes with poly(propylene glycol)-b-polystyrene block copolymer interfacial layer
(Natl Inst Science Communication-Niscair, 2017) Yıldırım, Mert; Allı, Abdulkadir; Demir, Ahmet; Allı, Sema; Gökçen, Muharrem
Polymeric materials have gained great importance in electron devices. There has been considerable number of studies on block copolymers due to enhanced features that appear after co-polymerization. In this study, poly (propylene glycol)-b polystyrene block copolymer has been synthesized and Schottky bather diodes (SBDs) have been fabricated with this block copolymer. Current-voltage (I-V) measurements have been conducted at room temperature in order to investigate electrical characteristics and current conductions governing in these SBDs. Series resistance and shunt resistance of the SBDs have been calculated using Ohm's law. Ideality factor, reverse saturation current and zero-bias bather height of the SBDs have been extracted from the forward-bias I-V data. Fabricated SBDs exhibited high rectifying ratio of the order 10(4). Also, current conduction mechanisms and the density of interface states in the SBDs have been investigated. Calculated values of density of interface states in the SBDs are on the order of 10(13) which is acceptable for this kind of SBDs having polymeric interfacial layer.
Current-voltage characteristics of Au/PLiMMA/n-Si diode under ultraviolet irradiation
(Pergamon-Elsevier Science Ltd, 2017) Çulcu, Hayat; Gökçen, Muharrem; Allı, Abdulkadir; Allı, Sema
Au/poly (linoleic acid)-g-poly(methyl methacrylate)(PLiMMA)/n-Si diode was fabricated and current-voltage (I-V) characteristics of this diode were measured in dark and under 365 nm ultra violet (UV) irradiation at room temperature. Main electrical parameters; such as leakage current (I-o) factor (n), zero-bias barrier height ((Phi B-o)) and surface states density (N-ss) were calculated using thermionic emission theory to obtain UV irradiation intensity dependence of these parameters. Also alternatively n, barrier height ((Phi(B))) and series resistance (Re) was calculated by Cheung & Cheung method. These alternatively obtained values were given and compared with the literature.
Current-voltage characteristics of Au/PLiMMA/n-Si diode under ultraviolet irradiation (vol 103, pg 197, 2017)
(Pergamon-Elsevier Science Ltd, 2017) Çulcu, Hayat; Gökçen, Muharrem; Allı, Abdulkadir; Allı, Sema
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Current-voltage characteristics of nano whisker ZnO/Si heterojunction under UV exposition
(Elsevier Science Sa, 2022) Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Gökçen, Muharrem; Doğruer, Musa; Altuğ, Cevher; Varilci, Ahmet
In/ZnO/p-Si heterojunction diode was produced to investigate the photo-responsivity and electrical features under ultraviolet (UV) light. A hydrothermal synthesis technique was used to coat the ZnO layer on the p-Si single crystal as nanowhisker/rods. The formation of surface and nanowhisker properties of the ZnO layer were investigated by scanning electron microscope (SEM). The I-V (current-voltage) analysis of the In/ZnO/p-Si diode was realized in dark and under UV (290-400 nm) illumination. Further, the main electrical parameters of the diode; such as reverse bias saturation current (I-V), ideality factor (n), zero bias barrier height (Phi(Bo)), resistance (R) and interface state density (N-ss) were obtained from the experimental I-V measurements by thermionic emission (TE) and Card and Rhoderick's function. Also, the power law of the photocurrents (I-PC), photoresponsivity (PR) and response time were extracted. Photo-responsivity and response time values of In/ZnO/p-Si heterojunction diode were obtained as 2.0 A/W and (rise/decay) 160/200 ms, respectively.
Dielectric and AC electrical conductivity characteristics of liquid crystal doped with graphene
(Edp Sciences S A, 2012) Gökçen, Muharrem; Yıldırım, Mert; Köysal, Oğuz
The dielectric response of the liquid crystal (LC) and LC doped with graphene was studied by using dielectric spectroscopy technique in the frequency range of 100 kHz to 10 MHz at room temperature. The LC material used in this experiment was E7 and the concentration of doping material graphene was acquired as 0.05 wt.% in E7. Dielectric constant (epsilon'), dielectric loss (epsilon ''), dielectric loss tangent (tan delta) and AC conductivity of pure LC and graphene-doped LC mixture were also calculated. Results showed that all dielectric parameters are strong functions of frequency and applied bias voltage. Also, it was found that doping LC with graphene strongly influenced threshold voltage.
Dielectric Properties of Au/PVA (Cobalt-Doped)/n-Si Photoconductive Diodes
(Springer, 2013) Gökçen, Muharrem
The voltage (V) and frequency (f) dependence of dielectric parameters such as the dielectric constant (epsilon'), dielectric loss (epsilon aEuro(3)), dielectric loss tangent (tan delta), real and imaginary parts of electrical modulus (M' and MaEuro(3)), and alternating-current (AC) electrical conductivity (sigma (AC)) of Au/PVA (cobalt-doped)/n-Si structures have been investigated by using experimental admittance measurements conducted at room temperature. The values of epsilon', epsilon aEuro(3), and tan delta were found to be strong functions of voltage and frequency, especially at low frequencies in the positive voltage region. It was observed that the values of epsilon' and epsilon aEuro(3) increase as the frequency decreases. The M' values increase with increasing frequency due to increasing dielectric relaxation, while MaEuro(3) values, in general, remain stable as frequency is changed. The sigma (AC) values at each bias voltage increase with increasing frequency.
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.
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.
The effect of PVA (Bi2O3-doped) interfacial layer and series resistance on electrical characteristics of Au/n-Si (110) Schottky barrier diodes (SBDs)
(Elsevier, 2012) Gökçen, Muharrem; Tunç, Tuncay; Altındal, Şemsettin; Uslu, İbrahim
Two types of Schottky Barrier Diodes (SBDs) with and without PVA (Bi2O3-doped) polymeric interfacial layer, were fabricated and measured at room temperature in order to investigate the effects of the PVA (Bi2O3-doped) interfacial layer on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (Phi(B0)), series resistance (R-s) and interface-state density (N-ss). Electrical parameters of these two diodes were calculated from the current-voltage (I-V) characteristics and compared with each other. The values of Phi(B0), n and R-s for SBDs without polymeric interfacial layer are 0.71 eV, 1.44 and 4775 Omega, respectively. The values of Phi(B0), n and R-s for SBDs with PVA (Bi2O3-doped) polymeric interfacial layer are 0.74 eV, 3.49 and 10,030 Omega, respectively. For two SBDs, the energy density distribution profiles of interface states (N-ss) were obtained from forward-bias I-V measurements by taking the bias dependence of R-s of these devices into account. The values of N-ss obtained for the SBD with PVA (Bi2O3-doped) polymeric interfacial layer are smaller than those of the SBD without polymeric interfacial layer. (C) 2011 Elsevier B.V. All rights reserved.
The effect of side-chain liquid crystalline concentration in liquid crystal on dielectric properties
(Pergamon-Elsevier Science Ltd, 2012) Gökçen, Muharrem; Köysal, Oğuz; Yıldırım, Mert; Altındal, Şemsettin
As liquid crystal (LC), E63 and as doping material, side-chain liquid crystalline polymer (SLCP) were used in this study. In order to observe the effect of SLCP concentration in LC on the dielectric properties in a wide range of frequency and bias voltage. SLCP was doped into E63 with 0 (pure E63), 1 and 10 wt%. The bias voltage and frequency dependence of the dielectric properties of pure E63 and doped mixtures (E63/SCLP) have been investigated using the admittance spectroscopy method (C-V and G/omega-V) in the frequency range of 10 kHz-10 MHz at room temperature. The values of dielectric constant (epsilon') and real (M') and imaginary (M '') parts of electric modulus of the pure E63 and E63/SLCP (1 and 10%) were calculated using the measured admittance values. Moreover, dielectric anisotropy (Delta epsilon) was also obtained for each sample as a function of frequency. Results show that the values of dielectric parameters are strong functions of frequency and applied bias voltage depending on the concentration amount. Furthermore, dielectric anisotropy has negative values according to p/n type changing for each sample after a critical frequency value. (C) 2012 Elsevier Ltd. All rights reserved.
The effects of Bi4Ti3O12 interfacial ferroelectric layer on the dielectric properties of Au/n-Si structures
(World Scientific Publ Co Pte Ltd, 2015) Gökçen, Muharrem; Yıldırım, Mert
Au/n-Si metal-semiconductor (MS) and Au/Bi4Ti3O12/n-Si metal-ferroelectricsemiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi4Ti3O12 decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.
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 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.
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.
The Fe3O4 nanoparticle doping effect in liquid crystal on electrical and dielectric properties
(Canadian Science Publishing, 2013) Köysal, Oğuz; Gökçen, Muharrem; Yıldırım, Mert
Fe3O4 nanoparticles were doped into E63 coded liquid crystal (LC) with 0.1 wt% to investigate the effect of Fe3O4 on the electrical and dielectric properties of LC in a wide range of frequency, bias voltage, and illumination. The frequency, bias voltage, and illumination level dependence of the electrical and dielectric properties of pure E63 and doped mixture (E63-Fe3O4) has been investigated using the current-voltage (I-V) and admittance spectroscopy (C-V and G/omega-V) data in the frequency range of 10 kHz - 1 MHz at room temperature. Results show that the increment in current with Fe3O4 doping is due to the metallic nature of the Fe3O4 nanoparticles. The current switching voltage of reorientation is shifted to lower voltage values as a result of Fe3O4 doping. Same behavior is also observed with increasing illumination level. The polarization contribution of Fe3O4 doping is evident considering the values of Delta epsilon' = epsilon'(E63/Fe3O4) - epsilon'(E63) at low frequencies. Moreover, depending on the existence of Fe3O4 doping agent, there is a split in sigma(ac)-f plots where sigma(ac) values increase with frequency, especially at high frequencies.
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.
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.
Illumination Effects on Electrical Characteristics of Au/Bi4Ti3O12/n-Si Structures
(Amer Scientific Publishers, 2015) Gökçen, Muharrem
The effects of illumination on electrical and photocurrent properties of Au/n-Si structures with and without Bi4Ti3O12 interfacial ferroelectric layer were investigated using current-voltage (I-V) and admittance measurements (C-V, G/omega-V). For this purpose, Au/n-Si metal-semiconductor (MS) and Au/Bi4Ti3O12/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and measured at dark and under various illumination intensity levels at room temperature. It was found that the ferroelectric interfacial layer increased the rectifying ratio by decreasing the leakage current and passivated the interface states. Furthermore, the photocurrent of MFS structure is more sensitive to illumination compared with that of MS structure, whereas the situation is opposite for interface states.

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