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Kahraman A.,Center for Nuclear Radiation Detector Research and Applications | Kaya S.,Center for Nuclear Radiation Detector Research and Applications | Kaya S.,Abant Izzet Baysal University | Jaksic A.,Tyndall National Institute | And 2 more authors.
Radiation Effects and Defects in Solids | Year: 2015

Radiation-sensing Field Effect Transistors (RadFETs or MOSFET dosimeters) with SiO2 gate dielectric have found applications in space, radiotherapy clinics, and high-energy physics laboratories. More sensitive RadFETs, which require modifications in device design, including gate dielectric, are being considered for personal dosimetry applications. This paper presents results of a detailed study of the RadFET energy response simulated with PENELOPE Monte Carlo code. Alternative materials to SiO2 were investigated to develop high-efficiency new radiation sensors. Namely, in addition to SiO2, Al2O3 and HfO2 were simulated as gate material and deposited energy amounts in these layers were determined for photon irradiation with energies between 20keV and 5MeV. The simulations were performed for capped and uncapped configurations of devices irradiated by point and extended sources, the surface area of which is the same with that of the RadFETs. Energy distributions of transmitted and backscattered photons were estimated using impact detectors to provide information about particle fluxes within the geometrical structures. The absorbed energy values in the RadFETs material zones were recorded. For photons with low and medium energies, the physical processes that affect the absorbed energy values in different gate materials are discussed on the basis of modelling results. The results show that HfO2 is the most promising of the simulated gate materials. © 2015 © 2015 Taylor & Francis.

Kahraman A.,Center for Nuclear Radiation Detector Research and Applications | Kahraman A.,Uludag University | Yilmaz E.,Center for Nuclear Radiation Detector Research and Applications | Yilmaz E.,Abant Izzet Baysal University | And 3 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2015

The purposes of this paper are to investigate the post deposition annealing (PDA) effect on structural and electrical characterizations of HfO2 MOS capacitor and the frequency dependency of series resistance and interface states in this device. PDA processes on the HfO2 films deposited using RF magnetron sputtering system were performed in N2 ambient at 350, 550, 650, and 750 °C. The phase identifications and crystallization degrees of the HfO2 films were determined by using X-ray diffractometry. The grain size of the films was varied from 4.5 to 15.23 with increasing in PDA temperature. The HfO2 MOS capacitors were fabricated using the as-deposited and annealed films for electrical characterization. C–V and G/ω–V measurements were performed at 1 MHz frequency. The C–V characteristics of the MOS capacitor fabricated with film annealed at 550 °C show a better behaviour in terms of the high dielectric constant and low effective oxide charge compared to others. For this device, C–V and G/ω–V measurements were performed in different frequencies ranging from 10 kHz to 1 MHz at room temperature. Obtained results show that series resistance and interface states strongly influence the C–V and G/ω–V behaviour of the MOS capacitor. © 2015 Springer Science+Business Media New York

Cetinkaya A.O.,Abant Izzet Baysal University | Cetinkaya A.O.,Center for Nuclear Radiation Detector Research and Applications | Kaya S.,Abant Izzet Baysal University | Kaya S.,Center for Nuclear Radiation Detector Research and Applications | And 5 more authors.
Thin Solid Films | Year: 2015

Bismuth ferrite (BiFeO3) thin films were deposited by sol-gel dip coating (SGDC) technique on Si-P(100) and glass substrates to investigate the structural and electrical characteristics. The aluminum (Al) metal contacts were formed on the samples deposited on the Si-P(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. The fabricated MOS structures were characterized electrically by capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements. The structural characterizations were performed by X-ray diffraction technique and scanning electron microscopy. The compositions of the films were investigated by energy-dispersive X-ray spectroscopy. The results exhibit that pure rhombohedral perovskite phase films were fabricated without any elemental contamination. Average grain sizes of the BiFeO3 deposited on silicon and glass wafers were found to be about 34,50 and 30,00 nm, respectively. In addition, while the thin films deposited on glass substrate exhibit porous surface, those deposited on Si-P(100) wafers exhibit dense microstructure with a homogenous surface. Moreover, the C-V and G/ω-V characteristics are sensitive to applied voltage frequency due to frequency dependent charges (Nss) and series resistance (Rs). The peak values of Rs have been decreased from 2,6 kω to 40 ω, while Nss is varied from 6,57 × 1012 to 3,68 × 1012 eV- 1 cm- 2 with increasing in frequency. Consequently, pure phase polycrystalline BiFeO3 thin films were fabricated successfully by SGDC technique and BiFeO3 dielectric layer exhibits stable insulation characteristics. © 2015 Elsevier B.V.

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