Betül Güzeldir

Electrical characteristics of Au/Ti/n-GaAs contacts over a wide measurement temperature range

We have fabricated Au/Ti/n-GaAs/In Schottky barrier diodes using the magnetron dc sputter technique. The capacitance–temperature (C–T) measurements with bias voltage as a parameter and the current–voltage (I–V) and capacitance–voltage (C–V) measurements have been made in the temperature range of 60–300 K. The temperature-dependent capacitance measurements have been made at 1.0 MHz. The capacitance versus temperature curve at each bias voltage has four regions with slopes different from each other. The capacitance decreases with a decrease in temperature at each bias voltage. Such a temperature-dependent behavior could be attributed to modulation of the space charge region caused by the emission of deep-level impurities or interface states. The carrier concentration calculated in the �1.0 to �2.0 V range of C �2 –V plots was close to the value of 7.43×10 15 cm �3 given by the manufacturer around room temperature. The ideality factor value from the I–V characteristics has remained almost unchanged between 1.07 and 1.10 in the temperature range of 150–300 K, indicating that the current across the device obeys the thermionic emission current model quite well over the whole bias range at temperatures above 150 K. Therefore, the conventional Richardson plot in this temperature range has given a Richardson constant of 8.21 A (cm K) �2 , within experimental error, which is in very close agreement with the theoretical value of 8.16 A (cm K) �2 for n-type GaAs. Again, it has been seen that the ideality factor with the values of 1.10 at 150 K and 1.22 at 60 K does not show a considerable decrease. The experimental parameters show that the Au(90 nm)/Ti(10 nm)/nGaAs contact is a good candidate for electronic device applications.

Using different chemical methods for deposition of copper selenide thin films and comparison of their characterization.

Different chemical methods such as Successive Ionic Layer Adsorption and Reaction (SILAR), spin coating and spray pyrolysis methods were used to deposite of copper selenide thin films on the glass substrates. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDX) spectroscopy and UV-vis spectrophotometry. The XRD and SEM studies showed that all the films exhibit polycrystalline nature and crystallinity of copper selenide thin films prepared with spray pyrolysis greater than spin coating and SILAR methods. From SEM and AFM images, it was observed copper selenide films were uniform on the glass substrates without any visible cracks or pores. The EDX spectra showed that the expected elements exist in the thin films. Optical absorption studies showed that the band gaps of copper selenide thin films were in the range 2.84-2.93 eV depending on different chemical methods. The refractive index (n), optical static and high frequency dielectric constants (ε0, ε∞) values were calculated by using the energy bandgap values for each deposition method. The obtained results from different chemical methods revealed that the spray pyrolysis technique is the best chemical deposition method to fabricate copper selenide thin films. This absolute advantage was lead to play key roles on performance and efficiency electrochromic and photovoltaic devices.

Investigation of the Electrical Characteristics of Al/p-Si/Al Schottky Diode

In this study, p-type Si semiconductor wafer with (100) orientation, 400 μm thickness and 1-10 Ω cm resistivity was used. The Si wafer before making contacts were chemically cleaned with the Si cleaning procedure which for remove organic contaminations were ultrasonically cleaned at acetone and methanol for 10 min respectively and then rinsed in deionized water of 18 MΩ and dried with high purity N2. Then respectively RCA1(i.e., boiling in NH3+H2O2+6H2O for 10 min at 60°C ), RCA2 (i.e., boiling in HCl+H2O2+6H2O for 10 min at 60°C ) cleaning procedures were applied and rinsed in deionized water followed by drying with a stream of N2. After the cleaning process, the wafer is immediately inserted in to the coating unit. Ohmic contact was made by evaporating of Al on the non-polished side of the p-Si wafer pieces under ~ 4,2 10-6 Torr pressure. After process evaporation, p-Si with omic contac thermally annealed 580°C for 3 min in a quartz tube furnace in N2. Then, the rectifier contact is made by evaporation Al metal diameter of about 1.0 mm on the polished surface of p-Si in turbo molecular pump at about ~ 1 10-6 Torr. Consequently, Al/p-Si/Al Schottky diode was obtained. The I–V measurements of this diode performed by the use of a KEITLEY 487 Picoammeter/Voltage Source and the C–V measurements were performed with HP 4192A (50–13 MHz) LF Impedance Analyzer at room temperature and in dark.

X- and gamma-ray irradiation effects on vanadium pentoxide thin films

Abstract Thickness and composition of thin films can be measured with X- and gamma-rays. In this work, thickness and composition of vanadium pentoxide thin films are investigated by energy dispersive and wavelength dispersive X-ray fluorescence systems. Also, the surface analysis of vanadium pentoxide thin films irradiated with Rhodium Kα X-rays and 59.54 keV gamma-rays emitted from 100 mCi and 5 Ci Americium-241 radioactive sources is performed by scanning electron microscope. It is observed that X- and gamma-rays are destructive for vanadium pentoxide thin films. Also, the composition of vanadium pentoxide thin films changes by irradiation with X- and gamma-rays.

Nanostructures and Properties of Vanadium Oxide Thin Film Prepared by Spray Pyrolysis Method

In this research, we reported structural, optical and morphological properties of va nadium oxide thin films directly grown on the glass substrates by fully automated spray pyrolysis equipment. The substrate temperature was set at 450 °C and the nozzle to substrate distance was optimized to be 20 cm. The precursor solution was prepared as 0.05 M by mixing 0.393 gr of vanadium trichloride (VCl3) in 50 mL of deionized water. The deposition parameters were 5 mL in 1 minute solution flow rate, 90° position of spray nozzle towards the substrate. Atmospheric air was used as carrier gas with 2.5 mbar pressure. Nanostructures and optical properties of as-grown films examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectrophotometer techniques. After thin films annealed at 500 °C, SEM, XRD and absorption measurements were taken again. The obtained results were compared.

Analysis of aging time dependent electrical characteristics of AuCu/n-Si/Ti Schottky type diode

The purpose of this study is to fabricate AuCu/n-Si/Ti Schottky type diode and determine the effects of aging time on the diode parameters such as ideality factor, barrier height, series resistance, interface state density and rectification ratio. Gold and copper ratios in the gold-copper alloy used in making the Schottky contact were taken as equal. Schottky barrier contact using AuCu alloy and ohmic contact using Ti metal were made on n-Si by thermal evaporation. The electrical characterization of the AuCu/n-Si/Ti diode was made immediately based on the aging time at room temperature in dark conditions. The I-V measurements were also repeated 1, 7, 15, 30 and 90 days after fabrication of the diode in order to observe the effect of the aging time. The determined values of the ideality factor are in the range of 1,21 (for immediately)-1,075 (for 90 days). In the same way, values of the barrier height are also in the range of 0,566 eV (for immediately)-0,584 eV (for 90 days). From the I-V characteristics, ...

Buildup factors and kerma for Al2O3 and SiO2 in the energy range 0.015-15 MeV

The energy absorption buildup factors (EABF) have been calculated for some thermoluminescent dosimetric materials (Al2O3 and SiO2) in the energy region 0.015-15 MeV up to the penetration depth of 40 mean free paths (mfp). Also, kerma relative to air has been determined for these materials. It is observed that the energy absorption buildup factors and kerma relative to air depend on the photon energy and chemical content. Also, the energy absorption build up factors are found the highest in intermediate energy whereas the lowest in low- as well as high energies.

Nanorods/nanostructral vanadium oxide prepared by spray pyrolysis

Nanorods/nanostructural vanadium oxide thin film was prepared on glass substrates by Spray Pyrolysis technique at a substrate temperature of 450 °C. The precursor solution was obtained by 0.1 M concentrations of VCl3 in de-ionize water. The structural, optical and morphological properties of this thin film was investigated by means of UV-vis spectrophotometer, X-ray diffraction (XRD), atomic-force microscopy (AFM) and scanning electron microscope (SEM). The optical result show that the optical gap is equal to 2.38 eV. The structural investigation conducted by X-ray diffraction showed that V5O9 thin film was polycrystalline with anorthic structure. SEM and AFM images revealed the formation of interconnected nanorods.

Characterization of deposited CdS thin films by Spray Pyrolysis method and used in Cd/CdS/p-Si/Al structure

In our study, as p-type crystalline Si substrate was used. Omic contact was performed by evaporating Al metal on the matt surface of crystal. On the other surface of it CdS thin film were enlarged with the technique of Spray Pyrolysis. Structural characteristics of the grown thin film was examined SEM and EDAX image. When examining SEM image of CdS thin film were totally covered the p-Si crystal surface of it was nearly homogeneous and The EDAX spectra showed that the expected different ratios metal percent exist in the alloys, approximately. On the CdS films whose surface features were investigated, at 10−7 torr pressure was obtained Cd/CdS/p-Si/Al sandwich structure by evaporating Cd. Firstly, the I-V (current-voltage) characteristics on 80K between 320K at room temperature of this structure was measured. I-V characteristics of the examined at parameters diodes calculation, Thermionic Emission, were used. The characteristic parameters such as barrier height and ideality factor of this structure have bee...