M. Altunbaş

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.

The effect of Ag diffusion on the crystal structure and electrical properties of Bi(Pb)SrCaCuO superconductors

X-ray diffraction of Bi(Pb)SrCaCuO compounds, prepared by a conventional solid-state technique, were measured from 20 degrees C to 500 degrees C. It was found that diffusion of Ag (600-825 degrees C) in Bi ceramics stimulates a high degree of grain orientation along the c-axis. In Ag-doped samples the lattice parameters a and c are decreased (in comparison with the undoped samples) and their dependences on temperature reveal a non-linear character. The critical temperature, determined from the resistivity measurements, for Ag-doped samples increased to 118 K. Ag diffusion at 790 degrees C increases the critical current density more than twice. The influence of low annealing temperature for Ag-doped samples on critical current density was also investigated. These results are discussed on the basis of precipitation of Ag solid solution in Bi(Pb)SrCaCuO superconductors.

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.

Diffusion of Ag in Bi(Pb)-Sr-Ca-Cu-O superconductors

Abstract The Ag diffusion in the superconducting oxide ceramic Bi 1.6 Pb 0.4 Sr 2 Ba 2 Cu 3 O x has been studied over the temperature range 350–800 °C using the technique of successive removal of thin layers and measurement of the sample resistivity. The temperature dependence of the Ag diffusion coefficient is given by the relation D = 5.2 × 10 −3 exp(−0.70/kT). The observed fast Ag diffusion is assigned to impurity migration through the defects of ceramic samples (the surface of pores, grain boundaries etc.). The current-voltage characteristics of AgBi(Pb)-Sr-Ca-Cu-OAg structures at room temperature became markedly degraded. It is discussed in relation to the redistribution of Ag via diffusion (with D ≈ 10 −12 cm 2 s −1 ) from the metallic layer into the superconductor.

Investigation of some physical properties of silver diffusion-doped YBa2Cu3O7?x superconductors

Silver diffusion in superconducting YBa2Cu3O7?x (YBCO) has been studied over the temperature range 500?800??C by x-ray diffraction measurements. The diffusion coefficient of Ag in YBCO was determined from the observed increase (0.12%) in the lattice parameter c as compared with the undoped sample. It was shown that the diffusion coefficient of Ag in the temperature range 500?800??C changed from 1 ? 10?10 to 5 ? 10?9?cm2?s?1 with an activation energy of about 1.06?eV. For the Ag-doped sample, the critical transition temperature and the critical current density were increased from 90 to 92.5?K and from 60 to 98?A?cm?2 respectively in comparison with those of undoped YBCO. The possible reasons for the observed increases in Tc and Jc due to Ag diffusion were discussed.

AC losses and irreversibility line of Bi(Pb)SrCa CuO high-tc superconductors

Abstract We performed measurements of χ′( T , H ac , f ) and χ′( T , H ac , f ) on a nominal composition of Bi 1.6 Pb 0.4 Sr 2 Ca 3 Cu

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.

Superconducting properties of gold-diffusion doped BiPbSrCaCuO

Abstract The crystal structure and superconducting properties of the gold-doped BiPbSrCaCuO have been investigated using X-ray diffraction, scanning electron microscope and electrical measurements. Doping of BiPbSrCaCuO was carried out by means of gold diffusion from an evaporated layer onto pellets at the sintering. It was found that the diffusion doping of pellets by gold stimulates formation of the Bi (2 2 2 3) phase, increases critical temperature and critical current density (from 33 A cm −2 for undoped sample to 112 A cm −2 for gold-doped BiPbSrCaCuO). Improving of structure and superconducting properties was discussed on the base of model related with retarding of the precipitation processes under the gold-diffusion doping technique used.

Production of BiPbSrCaCuO Thin Films on MgO and Ag/MgO Substrates by Electron Beam Deposition Techniques

Superconducting BiPbSrCaCuO thin films were prepared on MgO(001) and Ag/MgO substrates using an electron beam (e-beam) evaporation technique. The effects of annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties, respectively, were investigated by X-ray diffraction, atomic force microscopy, and by measurements of the critical temperature and the critical current density. It was shown that an annealing of both types of films at 845 or 860 °C resulted in the formation of mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c-axis perpendicular to the substrates. The slight increase of the critical temperature from 103 K to 105 K, the enhancement of the critical current density from 2 x 10 3 to 6 x 10 4 A/cm 2 , and the improved surface smoothness are due to a possible silver doping from the substrate.

The effect of Ag diffusion on properties of BiPbSrCaCuO thin films

Abstract Superconducting BiPbSrCaCuO films have been evaporated on Ag/MgO and MgO substrates (with and without Ag buffer layer) by the electron-beam technique. The influence of annealing temperature on the crystalline structure and superconducting properties of BiPbSrCaCuO films was investigated by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, critical temperature, critical current density and room temperature resistivity measurements. It was shown that the annealing of both types of films at 835°C resulted in formation of the mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c -axis perpendicular to the substrates. Annealing of films on Ag/MgO substrates is additionally accompanied by Ag diffusion from the buffer layer into BiPbSrCaCuO films. The higher rate of crystallization of the Bi-2223 and Bi-2212 phases, the higher degree of c -axis orientation, the higher dense surface morphology, the reduced lattice parameter c (by 0.6–0.8%) the reduced room temperature resistivity (2–3 times), the significantly enhanced critical temperature ( T c =106 K at R =0) and the critical current density ( J c = 1.1 × 10 4 A/cm 2 at 77 K) were observed for the Ag-doped films (on Ag/MgO substrates), in comparison with those for the undoped films (on MgO substrates). The temperature dependence of the Ag diffusion coefficient in Bi-2212 films in the range 650–800°C was described by the relation D =2.2×10 −5 exp(−1.2/ kT ).