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Kaya S.,Abant Izzet Baysal University | Kaya S.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Abant Izzet Baysal University | Yilmaz E.,Nuclear Radiation Detectors Research and Development Center
Journal of Radioanalytical and Nuclear Chemistry | Year: 2014

Effects of gamma-ray irradiation on the electrical characteristics of Al2O3 MOS capacitors such as barrier height, acceptor concentration, series resistance and interface state parameters have been studied by analyzing capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements. The fabricated MOS capacitors were irradiated with gamma-rays at doses up to five grays. C-V and G/ω-V measurements were recorded prior to and after irradiation at high frequency. The results show that the measured capacitance and conductance values decreased with increasing in irradiation dose and C-V and G/ω curves has been shifted toward the negative voltages. Moreover, the series resistance (Rs) and density of interface states increased with increasing in irradiation dose and density of interface states (Dit) were calculated as order of 1012 eV-1cm-2 prior to and after irradiation. Due to presence and variations in the Rs values, the corrected and the measured C-V and G/ω-V exhibited different behaviors. Therefore other electrical characteristics were assessed from corrected Cc characteristics. It was observed that acceptor concentration decreased with increasing in barrier height of device due to changes in interface states and diffusion potential. © 2014 Akadémiai Kiadó, Budapest, Hungary. Source


Malkas H.,Inonu University | Kaya S.,Abant Izzet Baysal University | Kaya S.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Abant Izzet Baysal University | Yilmaz E.,Nuclear Radiation Detectors Research and Development Center
Journal of Electronic Materials | Year: 2014

The effects of substrate temperature on the microstructure and morphology of CdZnTe thin films were investigated in detail. The CdZnTe thin films were deposited on glass substrates at 200°C, 300°C and 400°C by radio frequency magnetron sputtering and annealed at 450°C for an hour under N2 ambient at atmospheric pressure. The microstructure and morphology of the CdZnTe films were analyzed by using x-ray diffractometry, scanning electron microscopy, energy dispersive x-ray spectroscopy and atomic force microscopy. The effects of substrate temperature on transmission spectra of the CdZnTe films were also investigated. The experimental results show that the optimum morphology and crystalline thin film structures were achieved at 400°C growth temperature. At higher substrate temperatures, atomic mobility and diffusion are promoted, which can stabilize the uniformity and crystallite size. The crystalline grains enlarge and the surface morphology becomes smoother due to growth of grains in the CdZnTe thin films. In addition, the transmission spectra of the films are consistent with the morphological changes. It may be concluded that substrate temperature in growing CdZnTe films has a substantial effect on morphological characteristics, and desired quality of the CdZnTe thin films may be fabricated at higher substrate temperatures. © 2014 The Minerals, Metals & Materials Society. Source


Kaya S.,Abant Izzet Baysal University | Kaya S.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Abant Izzet Baysal University | Yilmaz E.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Tyndall National Institute
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2014

The possible usage of BiFeO3 (bismuth ferrite) in MOS (metal-oxide-semiconductor) based radiation sensors was studied. Gamma radiation effects on the electrical characteristics of BiFeO3 MOS capacitors were investigated in detail. BiFeO3 thin films were deposited on p (100)-type silicon wafers with a thickness of 300 nm by magnetron sputtering. To examine their gamma irradiation response over a range of doses, the fabricated MOS capacitors were irradiated using a Co-60 gamma source from 0.5 to 16 Gray at a dose rate of 0.0030 Gy/s. Capacitance-Voltage measurements were recorded prior to and after irradiation and the effects of radiation were determined from the mid-gap and flat-band voltage shifts. The results show that BiFeO 3 has a good response to gamma irradiation and can be used as a new material for future dielectric applications such as radiation sensors. © 2013 Elsevier B.V. All rights reserved. Source


Kaya S.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Nuclear Radiation Detectors Research and Development Center | Yilmaz E.,Abant Izzet Baysal University | Kahraman A.,Nuclear Radiation Detectors Research and Development Center | And 3 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2015

The frequency dependent irradiation influences on Sm2O3 MOS capacitors have been investigated and possible use of Sm2O3 in MOS-based radiation sensor was discussed in this study. To examine their gamma irradiation response over a range of doses, the fabricated MOS capacitors were irradiated up to 30 grays. Capacitance-Voltage (C-V) measurements were recorded for various doses and the influences of irradiation were determined from the mid-gap and flat-band voltage shifts. In addition, the degradations of irradiation have been studied by impedance based leakage current-voltage (J-V) characteristics. The results demonstrate that J-V characteristics have not been significantly change by irradiation and implying that the excited traps have a minor effect on current for given dose ranges. However, the frequency of applied voltage during the C-V measurements affects the irradiation response of devices, significantly. The variations on the electrical characteristics may be attributed to the different time dependency of acceptor and donor-like interface states. In spite of the variations on the device characteristics, low frequency measurements indicate that Sm2O3 is a potential candidate to be used as a dielectric layer in MOS based irradiation sensors. © 2015 Elsevier B.V.All rights reserved. Source


Kaya S.,Abant Izzet Baysal University | Kaya S.,Nuclear Radiation Detectors Research and Development Center | Lok R.,Abant Izzet Baysal University | Lok R.,Nuclear Radiation Detectors Research and Development Center | And 6 more authors.
Journal of Alloys and Compounds | Year: 2014

The frequency dependent electrical behavior of BiFeO3 MOS capacitors was studied in this work. BiFeO3 thin films were deposited on p-type Si (1 0 0) substrates at 0 C by RF magnetron sputtering and the structures were investigated by XRD and SEM measurements. Electrical characteristics of the capacitors were determined by C-V and G/ω-V measurements for several frequencies from 10 kHz to 1 MHz. The results illustrate that the C-V and G/ω-V characteristics of the devices are sensitive to both frequency and voltage variations. C-V characteristic variations decrease with increasing frequency and are mainly resulting from the presence of interface states (Ns) between silicon and BiFeO 3. The G/ω-V characteristics of devices were found to be different for low and high frequencies. Variations in G/ω-V characteristics in the low frequency regions (f < 500 kHz) decrease with increasing frequency, however, in high frequency regions they increase with increasing frequency. For high frequency (1 MHz) characteristics of the capacitor, the capacitance has been corrected by eliminating the effects of the series resistance (Rs) because of its negligible response to high frequency; however, for conductance measurements it cannot be ignored. The C-V and G/ω-V analysis demonstrate that Rs and Ns are important factors that can affect electrical characteristics of the capacitor. © 2013 Elsevier B.V. All rights reserved. Source

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