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    Analyses of temperature-dependent interface states, series resistances, and AC electrical conductivities of Al/p-Si and Al/Bi4Ti3O12/p-Si structures by using the admittance spectroscopy method
    (Iop Publishing Ltd, 2013) Yıldırım, Mert; Durmuş, Perihan; Altındal, Şemsettin
    In this study, Al/p-Si and Al/Bi4Ti3O12/p-Si structures are fabricated and their interface states (N-ss), the values of series resistance (R-s), and AC electrical conductivity (sigma(ac)) are obtained each as a function of temperature using admittance spectroscopy method which includes capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. In addition, the effect of interfacial Bi4Ti3O12 (BTO) layer on the performance of the structure is investigated. The voltage-dependent profiles of N-ss and R-s are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that N-ss and R-s, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of N-ss and the reordering and restructuring of N-ss under the effect of temperature. The values of activation energy (E-a), obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the E-a of the metal-ferroelectric-semiconductor (MFS) structure is found to be half that of the metal-semiconductor (MS) structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms (N-A), built-in potential (V-bi), Fermi energy (E-F), image force barrier lowering (Delta Phi(b)), and barrier height (Phi(b)), are extracted using reverse bias C-2-V characteristics as a function of temperature.
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    Controlling the electrical characteristics of Al/p-Si structures through Bi4Ti3O12 interfacial layer
    (Elsevier Science Bv, 2013) Durmuş, Perihan; Yıldırım, Mert; Altındal, Şemsettin
    In this study, the effects of high permittivity interfacial Bi4Ti3O12 (BTO) layer deposition on the main electrical parameters; such as barrier height, series resistance, rectifying ratio, interface states and shunt resistance, of Al/p-Si structures are investigated using the currentevoltage (I-V) and admittance measurements (capacitance-voltage, C-V and conductance-voltage, G/omega-V) at 1 MHz and room temperature. I-V characteristics revealed that, due to BTO layer deposition, series resistance values that were calculated by both Ohm's law and Cheung's method decreased whereas shunt resistance values increased. Therefore, leakage current value decreased significantly by almost 35 times as a result of high permittivity interfacial BTO layer. Moreover, rectifying ratio was improved through BTO interfacial layer deposition. I-V data indicated that high permittivity interfacial BTO layer also led to an increase in barrier height. Same result was also obtained through C-V data. Obtained results showed that the performance of the device is considerably dependent on high permittivity BTO interfacial layer. (C) 2013 Elsevier B.V. All rights reserved.
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    Correlation between barrier height and ideality factor in identically prepared diodes of Al/Bi4Ti3O12/p-Si (MFS) structure with barrier inhomogeneity
    (Elsevier Science Sa, 2017) Çetinkaya, H.G.; Yıldırım, Mert; Durmuş, Perihan; Altındal, Şemsettin
    This study aims to investigate electrical characteristics of identically prepared metal-ferroelectric-semiconductor (MFS) structures. Therefore a total number of 58 diodes were fabricated in the form of Al/Bi4Ti3O12/P-Si structure and then current-voltage (I-V) and admittance-voltage (C-V and G/omega-V) measurements were performed at room temperature. It was found that zero bias barrier height (Phi(Bo)) and ideality factor (n) show diode-to-diode variance. The value of n varied from 2.7 to 5.3 and such high values were attributed to the barrier height (BH) inhomogeneity, interfacial layer and surface states (N-ss). Similar behavior was observed for series resistance (R-s) values which were obtained by using Nicollian-Brews method. Other electrical parameters such as doping concentration of acceptor atoms (N-A), Fermi energy (E-F), and BH (Phi(B)) were extracted from reverse bias C-2-V characteristics. The experimental values of BH obtained from the forward bias I-V and reverse bias C-2-V characteristics varied from 0.69 to 0.84 eV and 0.75-0.93 eV and statistical analysis revealed mean BH values as 0.716 eV and 0.818 eV, respectively. We believe the variations in the electrical parameters are due to inhomogeneous interfacial layer and BH, non-uniformity of the interfacial traps or dislocations, and grain boundaries. (C) 2017 Elsevier B.V. All rights reserved.
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    Diode-to-diode variation in dielectric parameters of identically prepared metal-ferroelectric-semiconductor structures
    (Elsevier Science Sa, 2017) Çetinkaya, H.G.; Yıldırım, Mert; Durmuş, Perihan; Altındal, Şemsettin
    In this research, a total number of 58 diodes were fabricated in the form of Al/Bi4Ti3O12/p-Si structure and the voltage dependence of the real and imaginary parts of the complex dielectric constant (epsilon' and epsilon") and complex electric modulus (M' and M'') and ac electrical conductivity (sigma(ac)) of these diodes were investigated. It was also aimed to determine whether or not these parameters change from one sample to another and what kind of distribution exists for the identically fabricated samples. Mentioned parameters (e', e'', M', M'' and sac) were calculated using the capacitance and conductance data that were measured between -4 V and 4 V at 500 kHz at room temperature. Experimental results show that all of these parameters are strong functions of applied bias voltage especially in the depletion and accumulation regions. These changes are results of the restructuring and reordering of the surface states and their relaxation time under external electric field. Besides, it was found that there is diode-to-diode variation among the values of dielectric parameters which revealed double Gaussian distribution for the total 58 diodes. Thus, the results confirmed that investigating these parameters only for a single sample at a single bias voltage value cannot supply enough information on the dielectric properties and electric modulus. Therefore these parameters must be calculated in the wide range of bias voltage even for the identically prepared samples on the same semiconductor wafer. (C) 2017 Elsevier B.V. All rights reserved.
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    The effect of gamma irradiation on electrical and dielectric properties of organic-based Schottky barrier diodes (SBDs) at room temperature
    (Pergamon-Elsevier Science Ltd, 2012) Uslu, Habibe; Yıldırım, Mert; Altındal, Şemsettin; Durmuş, Perihan
    The effect of Co-60 (gamma-ray) irradiation on the electrical and dielectric properties of Au/Polyvinyl Alcohol (Ni,Zn-doped)/n-Si Schottky barrier diodes (SBDs) has been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements at room temperature and 1 MHz. The real capacitance and conductance values were obtained by eliminating series resistance (R-s) effect in the measured capacitance (C-m) and conductance (G(m)) values through correction. The experimental values of the dielectric constant (epsilon'), dielectric loss (epsilon ''), loss tangent (tan delta), ac electrical conductivity (sigma(ac)) and the real (M') and imaginary (M '') parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. In addition, the density distribution of interface states (N-ss) profile was obtained using the high-low frequency capacitance (C-HF-C-LF) method for before and after irradiation. The N-ss-V plots give two distinct peaks for both cases, namely before radiation and after radiation, and those peaks correspond to two different localized interface states regions at M/S interface. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect. (C) 2011 Elsevier Ltd. All rights reserved.
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    Effects of Frequency and Bias Voltage on Dielectric Properties and Electric Modulus of Au/Bi4Ti3O12/n-Si (MFS) Capacitors
    (Gazi Univ, 2017) Durmuş, Perihan; Bilkan, Çiğdem; Yıldırım, Mert
    In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor. Bismuth titanate (Bi4Ti3O12) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi4Ti3O12/n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (N-ss), series resistance (R-s), interfacial polarization and interfacial layer. It was found that R-s of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (N-ss) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of R-s and N-ss. The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of N-ss, R-s and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi4Ti3O12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO2 and SnO2. Therefore, a MFS capacitor with Bi4Ti3O12 interfacial layer can store more energy thanks to its high dielectric constant.
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    Effects of frequency and bias voltage ondielectric properties and electric modulus ofAu/Bi4Ti3O12/n-Si (MFS) capacitors
    (2017) Durmuş, Perihan; Bilkan, Çiğdem; Yıldırım, Mert
    In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor. Bismuth titanate (Bi4Ti3O12) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi4Ti3O12/n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (Nss), series resistance (Rs), interfacial polarization and interfacial layer. It was found that Rs of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (Nss) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of Rs and Nss. The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of Nss, Rs and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi4Ti3O12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO2 and SnO2. Therefore, a MFS capacitor with Bi4TiO12 interfacial layer can store more energy thanks to its high dielectric constant.
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    Electrical and Dielectric Properties of a n-Si Schottky Barrier Diode with Bismuth Titanate Interlayer: Effect of Temperature
    (Springer, 2017) Yıldırım, Mert; Şahin, C.; Altındal, Şemsettin; Durmuş, Perihan
    An Au/Bi4Ti3O12/n-Si Schottky barrier diode (SBD) was fabricated with a 51 nm Bi4Ti3O12 interfacial layer. Admittance measurements of the fabricated SBD were carried out in the bias voltage (V) range of -4 V and 6 V. Capacitance (C) and conductance (G/omega) measurements were carried out in a wide temperature range of 120-380 K so that temperature effects on electrical and dielectric properties of the SBD were investigated. Main electrical parameters were extracted from reverse bias C (-2)-V plots. It was found that variance of electrical and dielectric parameters of the SBD with temperature is basically different for low and high temperature regions. A fair number (similar to 10(12) eV(-1) cm(-2)) was obtained for surface states (N (ss)); however, N (ss) first decreased then increased with temperature. This result was associated with increased defects with temperature and higher activation energy in the high temperature region. Dielectric parameters of the SBD were also extracted and the dielectric constant of SBD was found as similar to 10 at room temperature. Application of modulus formalism to the admittance data revealed temperature-activated dielectric relaxation at 340 K. Results showed that the temperature has considerable effects on electrical and dielectric properties of Au/Bi4Ti3O12/n-Si SBD.
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    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.
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    Influence of interfacial layer thickness on frequency dependent dielectric properties and electrical conductivity in Al/Bi4Ti3O12/p-Si structures
    (A V S Amer Inst Physics, 2014) Durmuş, Perihan; Yıldırım, Mert
    Three Al/Bi4Ti3O12/p-Si structures were fabricated with different interfacial layer thickness values (10, 25, and 53 nm) and admittance measurements of the structures were carried out between 1 kHz and 1 MHz in order to investigate the influence of interfacial layer thickness on dielectric properties of these structures. For the structure with thicker interfacial layer, higher dielectric constant (epsilon') and dielectric loss (epsilon '') values were obtained at low frequencies. At high frequencies, these parameters tend to be saturated and become almost constant. Loss tangent versus frequency plots exhibit a peak and magnitude of the peak weakens with increasing frequency and shifts toward high frequency region. The dispersion in epsilon' and epsilon '' with varying thickness at low frequencies was ascribed to interfacial polarization. In addition, obtained epsilon '' values indicated higher energy dissipation in the structure with thicker interfacial layer. Admittance data of the structures were also considered in terms of modulus formalism to interpret the relaxation processes in the structures. Moreover, dc electrical conductivity values were derived using frequency dependent ac electrical conductivity of the structures. (C) 2014 American Vacuum Society.