İbrahim Yücedağ

Investigation of Electrical Characteristics in Al/CdS-PVA/p-Si (MPS) Structures Using Impedance Spectroscopy Method

The 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 [Φ_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, Φ_B(C-V) increases linearly. Therefore, both the measured capacitance (C_m) and conductance (G_m/w) 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.

On the frequency dependent negative dielectric constant behavior in Al/Co-doped (PVC+TCNQ)/p-Si structures

The dielectric properties, electric modulus and ac electrical conductivity (σac) of Al/Co-doped (PVC+TCNQ)/p-Si structures have been investigated in the wide frequency and voltage range of 0.5 kHz–3 MHz and (-4 V)–(9 V), respectively, using the capacitance-voltage (C–V) and conductance-voltage (G/ω–V) measurements at room temperature. The real and imaginary parts of dielectric constant (e′, e″), loss tangent (tan δ), σac and the real and imaginary parts of electric modulus (M′, M″) were found strongly function of frequency and applied voltage especially at low frequencies. The e′–V plot shows an anomalous peak in the forward bias region due to the series resistance (Rs), surface states (Nss) and interfacial layer (PVC+TCNQ) effects for each frequency and then it goes to negative values known as negative dielectric constant (NDC) at low frequencies (f ≤ 70 kHz). Such observation of NDC is important result because it implies that an increment of bias voltage produces a decrease in the charge on the electrodes. The amount of negativity e′ value increases with decreasing frequency and this decrement in the NDC corresponds to the increment in the e″.

Dielectric properties and electric modulus of Au/PPy/n-Si (MPS) type Schottky barrier diodes (SBDS) as a function of frequency and applied bias voltage

Au/PPy/n-Si Schottky barrier diodes (SBDs) were fabricated by forming polypyrrole (PPy) organic layer on n-Si using the spin coating technique. Frequency-dependent dielectric constant (e′), dielectric loss (e″), loss tangent (tan δ), real and imaginary parts of electrical modulus (M′ and M″) and AC electrical conductivity (σac) parameters of the structure were investigated in the frequency range of 10–500 kHz. It was found that the values of the e′, e″ and tan δ, in general, decrease with increasing frequency while an increase is observed in σac, M′ and M″. The tanδ and M″ also exhibit a peak at about zero-bias voltage, while peak intensity weakens with increasing frequency. The values of e′ and M′ decrease with increasing voltage while an increase is observed in e″, tan δ, σac and M″. These changes in e′, e″, tan δ, M′, M″ and σac values was attributed to surface charge polarization and the particular density distribution of surface states localized at PPy/n-Si interface.

Determination of type and quality of hazelnut using image processing techniques

Hazelnut (Corylus avellana L.) comes number two after almond in the ranking of hard shelled fruits that is cultivated commonly in the world. According to the FAO (Food and Agriculture Organization) statistics, Turkey covers approximately 70% of the world hazelnut production, and 82% of the hazelnut exportation. These statistics indicate that Turkey is the first largest hazelnut producer and exporter in the world. Quality and automation have a great importance in the agricultural industry that put our country forward as world-wide leader. In the quality control systems, classification studies with image processing methods have accelerated in recent years. In this study, it is aimed that determination of type and quality of shelled hazelnuts with image processing by using size and shape characteristics of hazelnuts. As a result of studies on a variety of hazelnuts, it was reached 84% accuracy rate for grouping of shelled hazelnut according to the type and commercial definitions. The quality of hazelnuts also was acquired without error. Inshell Hazelnut Standard (TS 3074) that is published by the Turkish Standards Institute (TSE) is based for shelled hazelnuts.

The Preparation of Transparent Organic Field Effect Transistor Using a Novel EDOT Functional Styrene Copolymer Insulator With a PEDOT:PSS Gate Electrode

In 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 (VTh), field effect mobility (μFET) and current on/off ratio (Ion/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 VTh, remarkable mobility, and Ion/off values.