E. Bacaksız

Production of CuInSe2 thin films by a sequential processes of evaporations and selenization

Thin films of copper indium diselenide (CuInSe2) were prepared by selenization of CuInSe2-Cu-In multilayered structure on glass substrate. The selenization procedure was carried out in a vapour of elemental selenium in a vacuum chamber. The obtained films were characterised by XRD and SEM measurements. The effects of substrate temperature on the structural, electrical and optical properties were studied. It was found that single phase CuInSe2 thin films with significant adhesion to substrate can be produced by selenization of CuInSe2-Cu-In multilayered structure at 450°C, when the first non single phase CuInSe2 layer was deposited at substrate temperature of 400°C. The thin films were found to be direct band gap semiconductors with a band gap of 0.97 eV.

Formation of p-type CdS thin films by laser-stimulated copper diffusion

A new fabrication technique of p-type CdS thin films by He-Ne laser illumination of bilayer Cu-nCdS structures at room temperature was investigated. The n-type CdS films were obtained by vacuum evaporation in a quasi-closed volume. X-ray diffraction was used to provide crystalline structure and composition data of CdS films and Cu-CdS structures. The band gap of CdS films was estimated from the optical transmission spectra. The hot probe and Hall effect studies were used for the determination of conductivity type and concentration of charge carriers in films. The formation of a p-n homojunction in CdS films or conversion of the film all over to the p-type, depending on the duration of laser illumination, was shown by I-V characteristics, the photovoltaic, the hot probe and Hall effect measurements. Analysis of concentration distributions of Cu in CdS films, arising as a result of laser-accelerated diffusion, by energy dispersive x-ray spectroscopy gave the effective diffusion coefficient of copper, D = 8 × 10-12 cm2 s-1 at T = 25 °C.

Light-assisted deposition of CdS thin films

The effects of white light illumination during the deposition of CdS thin films in a quasi-closed volume on the structural, photoelectrical and optical properties are investigated. The films were highly c-axis oriented with an increasing intensity of (002) reflection as the illumination increases. The room temperature resistivity values of the CdS films decreased in the range of 107-104???cm. The photosensitivity in the fundamental absorption region and the transparency in the transmission region considerably increased as the illumination increased. Under 100?mW?cm-2 insolation, the efficiencies of the CdS/CdTe solar cells based on CdS window materials which were deposited: (1) in the dark; and (2) under an illumination of 150?mW?cm-2; were found to be 1.8% and 7.3%, respectively.

LEVELS OF CESIUM RADIONUCLIDES IN LICHENS AND MOSSES FROM THE PROVINCE OF ORDU IN THE EASTERN BLACK SEA AREA OF TURKEY

Chemobyl nuclear power plant accident in Ukraine in April 26, 1986 has affected Scandinavia and European countries, the Balkans and the northside of Turkey. Radioactive clouds depending on meteorological conditions had contaminated soil surface and flora in the region of Thrace and the seaside of the Black sea. This study has been done on mosses and lichens in which radioactive isotopes can live for a long time. These specimens have been collected in various regions of Ordu located in the Eastern Black Sea region of Turkey. On the basis of the results of this study the geographic distribution of pollution on the flora has been done.

Role of Mg doping in the structural, optical, and electrical characteristics of ZnO-based DSSCs

ZnOand Mg-doped ZnO samples are prepared by spray pyrolysis on conducting glass substrates to fabricate ZnO-based dye-sensitized solar cells (DSSCs). Influences of Mg-doping content on the power conversion efficiencies of ZnO-based DSSCs are investigated. X-ray diffraction results show that all the samples exhibit a hexagonal wurtzite structure. Scanning electron microscopy data indicate that the ZnO sample has uniform rods with 1 μm diameter. With respect to ZnO, the band gap value of 4 at.% Mg-doped ZnO samples improves to the value of 3.27 eV and a further increase in Mg level up to 6 at.% gives rise to a decline in the band gap value of 3.22 eV. Photoluminescence measurements illustrate that intensities of the ultraviolet peak and a red luminescence peak take their maximum values for 4 at.% Mg doping. From solar cell performance measurements, the best power conversion efficiency of 0.08% is obtained for the doping amount of 4 at.% Mg.

Determination of Mass Attenuation Coefficients for CuInSe2 and CuGaSe2 Semiconductors

This work presents mass attenuation coefficients values of CuInSe2 and CuGaSe2 semiconductor thin films commonly used in photovoltaic devices. The mass attenuation coefficients were measured at different energies from 11.9 to 37.3 keV by using the secondary excitation method. Monochromatic photons were obtained using the Br, Sr, Mo, Cd, Te, Ba and Nd secondary targets. 59.5 keV gamma rays emitted from an annular Am‐241 radioactive source were used to excite secondary targets. Characteristic X‐rays emitted from secondary target were counted by a Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. The measured values were compared with theoretical values calculated using WinXCOM program.

Molybdenum diffusion in CuInSe2 thin films

Molybdenum diffusion in CuInSe2 (CIS) films was investigated in the temperature range 240-520°C using the energy-dispersive X-ray (EDX) and resistivity techniques. CuInSe2 thin films were deposited by single-source evaporation on glass and molybdenum-covered glass substrates. The temperature dependence of Mo diffusion coefficient is described by equation D=1.3×10-8exp (-0.53/kT). It is shown that the diffusion doping of p-type CIS by molybdenum is accompanied by the significant decrease of resistivity. The observed results of the diffusion and electrical measurements are attributed to migration of Mo in the polycrystalline CIS films by means of both along intergrain surfaces and into grains.