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Öğe Characterization of Surface States and Their Relaxation Time in Al/ZnO/p-GaAs Structure by Admittance Method at Room Temperature(Amer Scientific Publishers, 2019) Demir, Gülçin Ersöz; Yücedağ, İbrahim; Yerişkin, Seçkin AltındalSurface state (N-ss) density and their relaxation time (tau) of the fabricated Al/ZnO/p-GaAs structure was investigated in frequency range of 1 kHz-1 MHz and in voltage range of +/- 1.2 V. It was found that the variance of capacitance (C) and conductance (G/omega) with frequency and voltage is basically different especially at low and intermediate frequencies in depletion and accumulation regions. Characteristics of Al/ZnO/p-GaAs structure are affected by parameters such as N-ss, dipole and surface polarization in depletion region at low frequencies, while they are affected by parameters such as interfacial ZnO layer and series resistance (R-s) in accumulation region at higher frequencies. C and G have higher values in low frequency region due to effects such as N-ss in metal-semiconductor interface, interfacial ZnO layer and surface dipole polarization. The rise in C and G has been showed up thanks to the ac signal that can be easily monitored N-ss, strong interface and dipole polarizations, interfacial layer especially at weak inversion and depletion regions. Due to special distribution of N-ss at ZnO/p-GaAs interface, parallel conductance (G(p/omega)) - ln(f) plots show a peak under distinct voltage. Thus, the values of N-ss and omega were determined from the peak values of these plots and changed from 3.92 X 10(12) eV(-1) . cm(2) to 4.33 X 10(12) eV(1) . cm(2) and 6.3 X 10(5) s to 6.3X 10(6) s for 0.35 V and 1.1 V, respectively. These values of N-ss and 1.30 nm RMS roughness (from Atomic Force Microscopy (AFM) image) are very suitable for an electronic device.Öğe Controlling the electrical characteristics of Au/n-Si structure with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature(Wiley, 2017) Baraz, Nalan; Yücedağ, İbrahim; Demir, Ahmet; Demir, Gülçin Ersöz; Altındal, Şemsettin; Kandaz, MehmetIn order to interpret well whether or not the organic or polymer interfacial layer is effective on performance of the conventional Au/n-Si (metal semiconductor [MS]) type Schottky barrier diodes (SBDs), in respect to ideality factor (n), leakage current, rectifying rate (RR), series and shunt resistances (R-s, R-sh) and surface states (N-ss) at room temperature, both Au/biphenyl-CoPc/n-Si (MPS1) and Au/OHSubs-ZnPc/n-Si (MPS2) type SBDs were fabricated. The electrical characteristics of these devices have been investigated and compared by using forward and reverse bias current-voltage (I-V) characteristics in the voltage range of (-4V)-(4V) for with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature. The main electrical parameters of these diodes such as reverse saturation current (I-0), ideality factor (n), zero-bias barrier height (phi(B0)), RR, R-s and R-sh were found as 1.14x10(-5)A, 5.8, 0.6eV, 362, 44 and 15.9k for reference sample (MS), 7.05x10(-10)A, 3.8, 0.84eV, 2360, 115 and 270k for MPS1 and 2.16x10(-7)A, 4.8, 0.7eV, 3903, 62 and 242k for MPS2, respectively. It is clear that all of these parameters considerably change by using an organic interfacial layer. The energy density distribution profile of N-ss was found for each sample by taking into account the voltage dependence of effective barrier height (phi(e)) and ideality factor, and they were compared. Experimental results confirmed that the use of biphenyl-CoPc and OHSubs-ZnPc interfacial layer has led to an important increase in the performance of the conventional of MS type SBD. Copyright (c) 2015 John Wiley & Sons, Ltd.Öğe Electric and Dielectric Properties of Au/ZnS-PVA/n-Si (MPS) Structures in the Frequency Range of 10-200 kHz(Springer, 2017) Baraz, Nalan; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Demir, Gülçin Ersöz; Orak, İkram; Altındal, Şemsettin; Akbari, HosseinPure polyvinyl alcohol (PVA) capped ZnS semiconductor nanocrystals were prepared by microwave-assisted method, and the optical and structural properties of the as-prepared materials were characterized by x-ray diffraction (XRD) and Ultraviolet-visible (UV-Vis) techniques. The XRD pattern shows the formation of ZnS nanocrystals, and the UV-Vis spectroscopy results show a blue shift of about 1.2 eV in its band gap due to the confinement of very small nanostructures. The concentration of donor atoms (N (D)), diffusion potential (V (D)), Fermi energy level (E (F)), and barrier height (I broken vertical bar(B) (C-V)) values were obtained from the reverse bias C (-2)-V plots for each frequency. The voltage dependent profile of series resistance (R (s)) and surface states (N (ss)) were also obtained using admittance and low-high frequency methods, respectively. R (s)-V and N (ss)-V plots both have distinctive peaks in the depletion region due to the spatial distribution charge at the surface states. The effect of R (s) and interfacial layer on the C-V and G/omega-V characteristics was found remarkable at high frequencies. Therefore, the high frequency C-V and G/omega-V plots were corrected to eliminate the effect of R (s). The real and imaginary parts of dielectric constant (epsilon' and epsilon aEuro(3)) and electric modulus (M' and MaEuro(3)), loss tangent (tan delta), and ac electrical conductivity (sigma (ac)) were also obtained using C and G/omega data and it was found that these parameters are indeed strong functions of frequency and applied bias voltage. Experimental results confirmed that the N (ss), R (s) , and interfacial layer of the MPS structure are important parameters that strongly influence both the electrical and dielectric properties. The low values of N (ss) (similar to 10(9) eV(-1) cm(-2)) and the value of dielectric constant (epsilon' = 1.3) of ZnS-PVA interfacial layer even at 10 kHz are very suitable for electronic devices when compared with the SiO2. These results confirmed that the ZnS-PVA considerably improves the performance of Au/n-Si (MS) structure and also allow it to work as a capacitor, which stores electric charges or energy.Öğe Investigation of Electrical Characteristics in Al/CdS-PVA/p-Si (MPS) Structures Using Impedance Spectroscopy Method(Ieee-Inst Electrical Electronics Engineers Inc, 2016) Demir, Gülçin Ersöz; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Orak, İkram; Altındal, ŞemsettinThe cadmium sulfide (CdS) nanopowders have been prepared by ball-milling method, and CdS-polyvinyl alcohol (PVA) nanocompound in the form of film has been deposited on a p-Si wafer as an interfacial layer by spin-coating method. The impedance characteristics of the fabricated Al/CdS-PVA/p-Si (metal-polymer-semiconductor)-type structures were studied in the frequency and voltage range of 5 kHz-5 MHz and +/-1 V, respectively, by considering interface states (D-it), series resistance (R-s), and interfacial layer effects at 300 K. While the voltage and frequency dependence profiles of D-it were evaluated from the low-high frequency capacitance (C-LF-C-HF) and Hill-Coleman methods, R-s profiles were evaluated from the Nicollian and Brews method. Doping concentration atoms (N-A) and barrier height [Phi (B)(capacitance-voltage (C-V))] values were also obtained from the reverse bias C-2 versus V plots for each frequency. While D-it and R-s values decrease with increasing frequency almost exponentially, Phi (B)(C-V) increases linearly. Therefore, both the measured capacitance (C-m) and conductance (G(m)/omega) values were corrected to eliminate the R-s effect. The experimental results show that R-s value is more effective on the impedance measurements at high frequencies in the accumulation region, but D-it is effective at low frequencies in the depletion region.Öğe Investigation of photo-induced effect on electrical properties of Au/PPy/n-Si (MPS) type schottky barrier diodes(Springer, 2017) Demir, Gülçin Ersöz; Yücedağ, İbrahim; Bayrakdar, Sümeyye; Altındal, Şemsettin; Gümüş, AhmetAu/PPy/n-Si (MPS) type Schottky barrier diodes (SBDs) were produced and their current-voltage (I-V) characteristics were measured in the positive and negative bias regions at 300 K. The basic electronic quantities such as reverse-saturation current (I-o ), ideality factor (n), zero-bias barrier height (Phi(B0) ), series (R-s) and shunt resistances (R-sh) were obtained by using I-V data in total darkness and illumination (100 W/m(2)). The values of these parameters were found as 7.79 x 10(-9) A, 5.41, 0.75 eV, 1 k Omega and 130 M Omega in dark) and 4 x 10(-9) A, 4.89, 0.77 eV, 0.9 k Omega and 1.02 M Omega under illumination), respectively. Also the energy density distribution behaviors of surface states (N-ss ) have been acquired by calculation of effective barrier height (Phi(e) ) and ideality factor n (V) depending on voltage in total darkness and illumination. The values of N (ss) show an exponentially increase from the mid-gap of Si to the lower part of conduction band (E-c ) for two conditions. The possible current conduction mechanisms were determined by plotting of the double logarithmic I-V plots in the positive voltage zone and the value of current was found proportional to voltage (I similar to V (m) ). The high values of n and R-s were ascribed to the certain density distribution of N-ss localized at semiconductor /PPy interface, surface conditions, barrier inequality, the thickness of PPy interlayer and its roughness. The open-circuit voltage of the photodiode was found as 0.36 V under 100 W/m(2) illumination level. This is evidence that the fabricated sample is very sensitive to illumination. Therefore, it can be put into practice in optoelectronic industries as a photodiode or solar cells.Öğe Investigation of the Frequency and Voltage Dependent Dielectric Properties of Au/n-SiC Metal Semiconductor (MS) and Au/Al2O3/n-SiC Metal-InsulatorSemiconductor (MIS) Structures(2020) Demir, Gülçin Ersöz; Yücedağ, İbrahimIn this study, we investigated the fabrication of Au/n-SiC (MS) and Au/Al2O3/n-SiC (MIS) type structures with atomic layer deposition (ALD) technique and their dielectric properties. The dielectric characteristics of structures were analyzed at frequency range of 1 kHz-500 kHz and by applying a (-3V)-(9V) bias voltage at 300 K. The significant dielectric parameters such as dielectric constant (?') and dielectric loss (?"), real and imaginary parts of electrical modulus (M' and M"), loss tangent (tan) were calculated by depending on frequency and voltage from capacitance-voltage (C-V) and conductance-voltage (G/-V) data. Thereby, the effect of frequency on MS and MIS was searched in detail. The effect of the interface states occurred in the low frequency region can be attributed to the variation of the characteristic behavior of these parameters. It is clear that the dielectric parameters highly depend on the frequency and voltage at depletion and accumulation regions. Moreover, the peak position of M shifts to the left side of the graphic due to the effect of the insulating layer. It can be deduced from the obtained results that the interfacial polarization is easier at low frequencies. Also the interfacial polarization can contribute more to the variation of the dielectric properties.Keywords: Au/Al2O3/n-SiC (MIS) type structures, AC electrical conductivity, Dielectric Properties, Impedance measurements.Öğe Metal-polimer-yarıiletken (MPY) yapıların hazırlanması, elektriksel ve dielektrik özelliklerinin frekans ve sıcaklığa bağlı incelenmesi(Düzce Üniversitesi, 2018) Demir, Gülçin Ersöz; Yücedağ, İbrahimBu tez çalışmasında, CdS-PVA arayüzey tabakalı Al/p-Si Metal-Polimer-Yarıiletken (MPY) yapıların elektrik ve dielektrik parametreleri kapasitans-voltaj (C-V), kondüktans-voltaj (G/?-V) ve akım-voltaj (I-V) ölçümlerinden yararlanılarak incelenmiştir. CdS-PVA nanoparçacıkları bilyalı öğütme metodu kullanılarak oluşturuldu ve p-Si üzerine sol-jel metodu ile kaplanmıştır. Omik ve doğrultucu kontaklar termal buharlaştırma yöntemiyle oluşturularak Al/(CdS-PVA)/p-Si yapılarının üretim süreci tamamlanmıştır. Al/(CdS-PVA)/p-Si yapıların yapısal özellikleri; Ultraviyole ve görünür ışık (UV-VIS), X-Ray Powder Diffraction (XRD) ve Scanning Elektron Mikroskobu (SEM) ile incelenirken, kompleks dielektrik (?', ?''), kayıp tanjant (tan?), ac elektriksel iletkenlik (?ac), kompleks elektriksel modülüs (M', M'') gibi dielektrik özellikleri 5 kHz-5 MHz frekans, ±1.0 V voltaj ve 500 kHz'de 230-340 K sıcaklık aralığında analiz edilmiştir. Yüksek frekanslarda ve düşük sıcaklıklarda ?', ?'', tan? ve ?ac değerleri neredeyse sabitken, düşük frekanslar ve yüksek sıcaklıklarda ?', ?'', tan? ve ?ac değerleri ac sinyalini kolayca takip edebilen Nss ve arayüzey polarizasyonlarından dolayı artış göstermektedir. M' ve M'' değerlerinin artan frekans ile birlikte artarken, sıcaklığın artışı ile azaldığı görülmektedir. Bu durum, dc gerilim, frekans ve sıcaklığın etkisi ile arayüzey yüklerin yeniden yapılanıp-düzenlenmesine atfedilmiştir. Al/(CdS-PVA)/p-Si yapıların relaksasyon mekanizmasını belirlemek için M' ve M'' parametrelerinin Argand diyagramları sıcaklığın fonksiyonu olarak incelenmiştir. Arayüzey durumlarının yoğunluğu (Nss)'nin voltaj ve frekansa bağlı özellikleri düşük-yüksek frekanslı kapasitans (CLF-CHF) ve Hill-Coleman yöntemleri ile incelenirken, Rs değerleri Nicollian ve Brews yöntemleri ile elde edilmiştir. Nss ve Rs değerleri artan frekans ile azalmıştır ve Rs etkisini ortadan kaldırmak için düzeltilmiş kapasitans (Cc) ve düzeltilmiş iletkenlik (Gc/?) grafikleri oluşturulmuştur.Öğe On the Frequency-Voltage Dependence Profile of Complex Dielectric, Complex Electric Modulus and Electrical Conductivity in Al/ZnO/p-GaAs Type Structure at Room Temperature(Amer Scientific Publishers, 2019) Yerişkin, Seçkin Altındal; Demir, Gülçin Ersöz; Yücedağ, İbrahimThe real and imaginary parts of complex dielectric parameters (epsilon', epsilon ''), complex electrical modulus (M', M ''), and ac electrical conductivity (sigma(ac)) of Al/ZnO/p-GaAs type structure were studied as a function of frequency and voltage through the Impedance Spectroscopy Method. For this purpose, both the capacitance (C) and conductance (G/omega) of the structure was carried out at wide frequency range (1 kHz-1 MHz) and voltage range (+/- 1.2 V). It is indicated that these parameters are considerably sensitive to relatively-low and medium frequency and voltage. The change of the parameters with frequency and voltage is thought to depend on circumstances of surface states (N-ss) and ZnO interlayer at the interface/semiconductor interface, interface-dipole polarization, and series resistance. While polarization and N-ss are active at low and medium frequency in the depletion and accumulation regions, series resistance (R-s) is active at high frequencies in the layer of accumulation. It is also found that epsilon', epsilon '', loss tangent (tan delta), and R-s decrease together with rising frequency whereas M', M '' and sigma(ac) increase under the same circumstances. The results indicated that interface-dipole polarization and N-ss can emerge more easily depending on the relaxation/lifetime of the surface states at low frequencies. The peak amplitude in the M '' - V graphics increase together with rising frequency and the peak locations move to the accumulation region because of the charges in the traps and relaxation polarization.Öğe The Preparation of Transparent Organic Field Effect Transistor Using a Novel EDOT Functional Styrene Copolymer Insulator With a PEDOT:PSS Gate Electrode(Springer, 2018) Günaydın, Okan; Demir, Ahmet; Demir, Gülçin Ersöz; Yücedağ, İbrahim; Coşut, BünyeminIn this study, we have purposed to combine both polystyrene (PS) and 3,4-ethylenedioxythiophene (EDOT) groups as a gate dielectric and to fabricate a transparent organic field effect transistor (OFET) device with polymeric gate electrode using this novel organic dielectric material. The focus point of this work is to obtain a transparent OFET and to minimize the interface states between gate insulator and gate electrode. Firstly, we have synthesized EDOT functional polystyrene (PS-EDOT) copolymer as gate insulator via "click" chemistry between azide-functional styrene copolymer and propargyl-functionalized EDOT. We used the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) conductive polymer mixture as a suitable alternative gate electrode instead of inorganic contacts, which is a new topic in the organic electronics. The contact resistance value was measured as 1/600 (S/cm)(-1). At the end of the process transparent OFETs with different channel length were fabricated using spin coating method by which poly(3-hexylthiophene) (P3HT), novel PS-EDOT copolymer insulator and PEDOT:PSS were coated on prepatterned OFET substrate. Electrical characterizations of OFET devices were held in total darkness and in air ambient in order to achieve output and transfer current-voltage (I-V) characteristics. The main parameters such as the threshold voltage (V (Th) ), field effect mobility (mu FET) and current on/off ratio (I (on/off) ) of the devices were extracted from capacitance-frequency (C-f) plot. It was found that fabricated PS-EDOT OFETs exhibit good device performances such as low V (Th) , remarkable mobility, and I (on/off) values.Öğe Temperature and Interfacial Layer Effects on the Electrical and Dielectric Properties of Al/(CdS-PVA)/p-Si (MPS) Structures(Springer, 2018) Demir, Gülçin Ersöz; Yücedağ, İbrahim; Kalandaragh, Yashar Azizian; Altındal, ŞemsettinIn the present study, cadmium sulphide (CdS) nanopowders were prepared by using a simple physical ball milling technique, and their x-ray diffraction (XRD) analysis confirmed the formation of hexagonal wurtzite structure of CdS. The morphology of CdS nanopowders was characterized by scanning electron microscope (SEM). Dielectric and electrical properties of the manufactured Al/(CdS-PVA)/p-Si (MPS) type structures were investigated by capacitance-voltage (C-V) and conductance-voltage (G/-V) measurements as functions of temperature and applied bias voltage at 500kHz. Some main parameters of the structure such as real and imaginary parts of complex dielectric constants, epsilon(=epsilon-j epsilon), loss tangent (tan), a.c. electrical conductivity (sigma(ac)), and real and imaginary parts of complex electric modulus, M*(=M+jM) of the structure were investigated in the temperature range between 230K and 340K. Ln(sigma(ac))-q/kT curve showed a linear behavior. The value of activation energy (E-a) was obtained as 0.0601eV at 5.0V from the slope of this curve. Moreover, argand diagrams of complex modulus were studied to determine relaxation process of these structures.