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Tugay E.,Middle East Technical University | Tugay E.,Center for Solar Energy Research and Applications | Yilmaz E.,Abant Izzet Baysal University | Turan R.,Middle East Technical University | Turan R.,Center for Solar Energy Research and Applications
Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films | Year: 2012

The authors studied effects of gamma radiation on the electrical properties of the MOS capacitor mČadež on SiN x thin films with thickness of 100 nm deposited on p-type (100) silicon wafer using plasma-enhanced chemical vapor deposition method. The authors investigated the chemical bonds and their densities inside the films using Fourier transform infrared (FTIR) spectroscopy. The as-deposited and annealed samples with Al/SiN x/Si structure as metal-insulator-semiconductor (MIS) capacitors were exposed to a 60-Co gamma radiation source with a dose rate of 0.015 Gy/S. The authors performed capacitance-voltage measurements at frequencies 10, 100, and 1000 kHz before and after radiation exposure with doses of up to 40 Gy. It was found that before gamma irradiation compared with as-deposited sample, the annealed samples exhibit less negative flatband voltages (V fb) shift. This indicates the relative reduction in positive charge in the SiN x:H samples. After gamma irradiation, for all samples a negative shift has been observed in V fb, being more pronounced in the samples annealed at 700 °C. The more striking feature is that the amount of shift does not change by increasing radiation dose after first irradiation, in which we attributed what to the radiation hardening in Al/SiN x/Si MIS capacitors. © 2012 American Vacuum Society.


Saleh Z.M.,Center for Solar Energy Research and Applications | Saleh Z.M.,Arab American University - Jenin | Nasser H.,Center for Solar Energy Research and Applications | Ozkol E.,Center for Solar Energy Research and Applications | And 4 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2015

Plasmonic interfaces integrated to the front, back and both surfaces of photovoltaic thin films show different degrees of enhancement of light trapping. Enhancements in the spectral dependence of photocurrent normalized to the power of excitation light are used as an indicator of enhanced light trapping. In a previous study, we obtained enhancement in the spectral range of 600-700 nm by integrating 100-nm Ag nanoparticles to the back surface of a-Si:H with a critical dependence on the SiNx spacer layer thickness. In this study, we compare the enhancement in photocurrent due to plasmonic interfaces integrated to the front, back and both front and back surfaces of the a-Si:H absorber. Interfaces integrated to the back result in the largest enhancement in photocurrent while those integrated to the front give the lowest. The marginal enhancements due to two interfaces appear to be mainly due to the back interface. While plasmonics effects may not account for the total enhancement in photocurrent, it explains the relative enhancement in the spectral range of 550-700 rather well. For all configurations, the enhancement in the spectral dependence of photocurrent is accompanied by broadening into the red of the localized surface plasmon resonance (LSPR). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Gullu H.H.,Middle East Technical University | Gullu H.H.,Center for Solar Energy Research and Applications | Coskun E.,Canakkale Onsekiz Mart University | Parlak M.,Middle East Technical University | Parlak M.,Center for Solar Energy Research and Applications
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2015

In this work, zinc selenide (ZnSe) thin films were deposited by thermal evaporation method using pure elemental (Zn and Se) sources. The physical properties of the films have been investigated in terms of the structural and optical characterizations depending on the post-annealing process under nitrogen atmosphere in the temperature between 300 and 500 °C for 30 min. The structural and compositional analyses were carried out by means of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The compositional analysis indicated that the deposited films were nearly stoichiometric whereas there was a decrease in Se and increase in the Zn contents. This implies the segregation and/or reevaporation of Se atoms from the thin film structure. The optical characteristics were studied by using the room temperature transmission measurements. The analysis of transmission values showed that the band gap values changed in between 2.38 and 2.62 eV depending on the annealing temperatures. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Coskun E.,Middle East Technical University | Coskun E.,Canakkale Onsekiz Mart University | Coskun E.,Center for Solar Energy Research and Applications | Gullu H.H.,Middle East Technical University | And 5 more authors.
Journal of Low Temperature Physics | Year: 2014

The structural properties and electrical conduction mechanisms of Ag–Ga–In–Te thin films deposited by a combination of e-beam and thermal evaporation methods were studied for various annealing temperatures. Structural analysis showed the existence of In(Formula presented.) and In(Formula presented.) binary phases at the early stage of crystallization and monophase of AgGa(Formula presented.) with the main orientation along (112) direction following the post-annealing at 400 (Formula presented.)C. The effects of the structural changes on electrical properties and temperature dependence of the electrical conductivity of Ag–Ga–In–Te thin films were studied in the temperature range of 90–400 K. The analysis of electrical conductivity revealed the Efros–Shklovskii variable range hopping (VRH) mechanism in between 90 and 210 K and Mott VRH mechanisms for the temperature range of 250–400 K for all deposited films. The VRH parameters including average hopping distance, average hopping energy and characteristic temperature coefficient for Efros–Shklovskii and Mott VRH mechanisms were determined and discussed in detail. © 2014, Springer Science+Business Media New York.


Coskun E.,Middle East Technical University | Coskun E.,Canakkale Onsekiz Mart University | Coskun E.,Center for Solar Energy Research and Applications | Gullu H.H.,Middle East Technical University | And 9 more authors.
Materials Science in Semiconductor Processing | Year: 2015

In this work, p-(Ag-Ga-In-Te) polycrystalline thin films were deposited on soda-lime glass and n-type Si substrates by e-beam evaporation of AgGa0.5In0.5Te2 crystalline powder and the thermal evaporation of Ag powder, sequentially in the same chamber. The carrier concentration and mobility of the Ag-Ga-In-Te (AGIT) film were determined as 5.82×1015 cm-3 and 13.81 cm2/(V s) as a result of Hall Effect measurement. The optical analysis indicated that the band gap values of the samples were around 1.58 eV. The structural analysis was carried out by means of X-ray diffraction. Current-Voltage (I-V) measurements depending on the sample temperature were performed to investigate the device characteristics and the dominant conduction mechanism in an In/p-AGIT/n-Si/Ag structure. The series and shunt resistances were calculated by the help of parasitic resistance analysis as 5.73 and 1.57×104 Ω cm2, respectively at room temperature. The ideality factors and barrier heights were evaluated as a function of sample temperature. In the low bias region, the thermionic emission together with the generation-recombination mechanism was investigated as the dominant transport mechanism; however, in the high bias region, space charge limited current was analyzed as the other effective mechanism in the carrier conduction. The built-in potential of the device was also determined by the help of capacitance-voltage measurements. © 2015 Elsevier Ltd.

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