Yazar "Karabulut, A." seçeneğine göre listele

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    Capacitance-conductance characteristics of Au/Ti/Al2O3/n-GaAs structures with very thin Al2O3 interfacial layer
    (Iop Publishing Ltd, 2015) Turut, A.; Karabulut, A.; Ejderha, K.; Biyikli, N.
    High-k Al2O3 with metallic oxide thickness of about 3 nm on n-type GaAs substrate has been deposited by the atomic layer deposition (ALD) technique. Thus, it has been formed the Au-Ti/Al2O3/n-GaAs MIS structures. It has been seen that the MIS structure exhibits excellent capacitance-voltage (C-V) and current-voltage (I-V) properties at 300 K. The saturation current of the forward bias and reverse bias I-V characteristics was the same value. An ideality factor value of 1.10 has been obtained from the forward bias I-V characteristics. The C-Vcharacteristics of the structure have shown almost no hysteresis from +3 V to -10 V with frequency as a parameter. The reverse bias C-V curves have exhibited a behavior without frequency dispersion and almost hysteresis at each frequency from 10 kHz to 1000 kHz.
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    Capacitance-conductance-current-voltage characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures
    (Elsevier Sci Ltd, 2015) Turut, A.; Karabulut, A.; Ejderha, K.; Biyikli, N.
    We have studied the admittance and current-voltage characteristics of the Au/Ti/Al2O3/n-GaAs structure. The Al2O3 layer of about 5 nm was formed on the n-GaAs by atomic layer deposition. The barrier height (BH) and ideality factor values of 1.18 eV and 2.45 were obtained from the forward-bias In I vs V plot at 300 K. The BH value of 1.18 eV is larger than the values reported for conventional Ti/n-GaAs or Au/Ti/n-GaAs diodes. The barrier modification is very important in metal semiconductor devices. The use of an increased barrier diode as the gate can provide an adequate barrier height for FET operation while the decreased barrier diodes also show promise as small signal zero-bias rectifiers and microwave. The experimental capacitance and conductance characteristics were corrected by taking into account the device series resistance Rs. It has been seen that the noncorrection characteristics cause a serious error in the extraction of the interfacial properties. Furthermore, the device behaved more capacitive at the reverse bias voltage range rather than the forward bias voltage range because the phase angle in the reverse bias has remained unchanged as 90 independent of the measurement frequency. (C) 2015 Elsevier Ltd. All rights reserved.
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    Characterization of aluminum 8-hydroxyquinoline microbelts and microdots, and photodiode applications
    (Pergamon-Elsevier Science Ltd, 2020) Sevgili, O.; Canli, S.; Akman, F.; Orak, I; Karabulut, A.; Yildirim, N.
    In the present study, we investigated the electrical, optical, and photoresponse characteristics of aluminum 8-hydroxyquinoline (Alq3)/silicon heterojunctions. The Alq3 thin film was successfully coated using the spin coating method on p-type Si. In order to determine the energy band gap diagram, the highest occupied molecular orbital-lowest unoccupied molecular orbital energy diagram was simulated with the density functional theory program. The quality of the coating and morphological properties of the Alq3 thin film were characterized using atomic force microscopy and scanning electron microscopy. The optical characteristics of the organic layer were investigated using ultraviolet-visible spectrophotometry. A reference diode was also fabricated with an Alq3/pSi photodiode to obtain a better understanding of the electrical and optical properties of the device. The photodiode and diode parameters comprising the saturation current, ideality factor, barrier height, short circuit current, open circuit voltage, fill factor, and power conversion efficiency were obtained from the current-voltage measurements. These measurements were performed in the dark and under different illumination conditions at room temperature. The experimental results showed that the properties of the photodiode device were improved by using organic Alq3 microdots, and thus the device may have optoelectronic and photovoltaic applications.
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    Cu-Al-Mn shape memory alloy based Schottky diode formed on Si
    (Elsevier, 2019) Aldirmaz, E.; Tataroglu, A.; Dere, A.; Guler, M.; Guler, E.; Karabulut, A.; Yakuphanoglu, F.
    In this work, martensite was made over the wide temperature ranges and the two forms of martensite morphology in Cu85.41Al9.97Mn4.62 shape memory alloy (SMA) were beta' and gamma' martensite phases. The SMA was characterized by the use of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. In order to fabricate the Schottky diode, Cu-Al-Mn alloy was used as a Schottky contact on p-type Si semiconductor substrate. Some of the crucial parameters for diodes such as ideality factor and barrier height values were obtained from electrical measurements. Illumination-dependent measurements showed that the fabricated device presents the behaviors of photodiode and photoconducting. Besides, it is found that the fabricated diode's structure is sensitive to illumination. Frequency-dependent measurements also indicated that the series resistance and interface state parameters are crucial to affect electrical characteristics of the fabricated diode. The experimental results showed that the fabricated Schottky device could be used in variety of optoelectronic applications.
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    Electrical characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures over a wide measurement temperature
    (Natl Inst Optoelectronics, 2017) Turut, A.; Karabulut, A.; Efeoglu, H.
    We have prepared the Au/Ti/Al2O3/n-GaAs structures and investigated their current-voltage (I-V) characteristics with the temperature (in 20-320K range) as a parameter, and current-temperature (I-T) characteristics with bias voltage as a parameter. The ultrathin Al2O3 metal-oxide layer on the n-GaAs substrate has been formed by atomic layer deposition (ALD) method. Ti(10nm) rectifying contacts have been fabricated on Al2O3/n-GaAs structure by DC magnetron sputtering. The ideality factor value has remained between 1.10-1.06 from 130 K to 320 K. The barrier height (BH) value has increased with a slope of alpha = -0.31 meV/K from 320 K to 110 K. Then, it has been seen that the decrease in the BH value from 110 K to 20 K obeys a double Gaussian distribution (GD) of the BHs due to the BH inhomogeneity. The experimental I-T characteristics have been interpreted by plotting the theoretical I-T characteristics with and without the GD based on the TE current theory at each bias voltage. Moreover, the BH values have been also determined from the Richardson curves plotted using the I-T data at each forward and reverse bias voltage. It has been observed that the BH reduction is higher under reverse bias voltage than under forward bias voltage regime due to the barrier inhomogeneity which is not recommended for the Schottky diode being a rectifying device.
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    Fabrication of Ni, Cr, W reinforced new high alloyed stainless steels for radiation shielding applications
    (Elsevier, 2019) Aygun, B.; Sakar, E.; Korkut, T.; Sayyed, M. I.; Karabulut, A.; Zaid, M. H. M.
    Stainless steel is commonly used in radiation applications for its high temperature resistance and fine mechanical properties. In this study, three types of high alloyed stainless-steel samples were produced. Before the production, GEANT4 Monte Carlo simulation toolkit was used to estimate the total fast neutron macroscopic cross sections and gamma mass attenuation coefficients. The hot-pressing process and the powder metallurgy method were applied. We tested samples' chemical and mechanical strength. Samples were exposed to both gamma rays and fast neutrons. The obtained simulation and experimental results for both neutron and gamma radiation are compatible. According to the simulation and experimental results, neutron shielding capacity of the new stainless-steel alloys is higher than the most commonly used 316LN stainless steel in nuclear applications. Among the prepared samples, SSA1 steel has the smallest half value layer at the all examined energies. All the prepared samples posses higher mass attenuation coefficient values and lower half value layer than 316LN steel. This indicates that the produced three new high alloyed stainless-steel samples have high gamma absorption capacity when compared to 316LN steel.
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    Investigation of temperature dependent negative capacitance in the forward bias C-V characteristics of (Au/Ti)/Al2O3/n-GaAs Schottky barrier diodes (SBDs)
    (Elsevier Sci Ltd, 2019) Guclu, C. S.; Ozdemir, A. F.; Karabulut, A.; Kokce, A.; Altindal, S.
    In this study, a metal-insulator-semiconductor (MIS) type Schottky barrier diodes (SBDs) were fabricated by growing a thin Al2O3 insulator layer between Au/Ti and n-GaAs using atomic layer deposition (ALD) method. The effect of temperature and voltage on interface states (N-ss) and series resistance (R-s) of the (Au/Ti)/Al2O3/n-GaAs (MIS) type Schottky barrier diodes (SBDs) was investigated using the capacitance/conductance-voltage (C/ (G/omega-V) data measured in wide range of temperature (200-380 K) and voltage (+/- 5 V). It was found that C and G/omega are strongly dependent on temperature and voltage. The value of C in the forward bias region reaches to maximum and then becomes negative. This negative capacitance (NC) behavior of this SBD is observed for each temperature level. Also, capacitance-current (C-I) and conductance-current (G/omega-I) plots were drawn to explain the NC behavior. The negative value of C in the accumulation region corresponds to the maximum value of G/omega. Such behavior of C can be explained by the loss of interface charges located at (Al2O3)/n-GaAs interface because of impact ionization process, the existence of surface states (N-ss), series resistance (R-s) and interfacial of (Al2O3) oxide layer.Therefore, the voltage dependent profiles of R-s and N-ss were obtained using Nicollian-Brews and Hill-Colleman methods for enough high forward biases as a function of temperature at various positive bias voltages. The changes in R-s and N-ss values were attributed to restructure and reordering of the carriers under temperature and voltage effects.