Showing papers by "Petko Vitanov published in 2007"

XPS characterization of thin ZrO 2 and (ZrO 2 ) x (Al 2 O 3 ) 1-x films deposited on silicon

Abstract: The study deals with thin films of zirconia (ZrO 2 ) and (ZrO 2 )x(Al 2 O 3 ) 1-x , deposited on silicon substrates, using the chemical solution deposition method. The thin films were obtained by spin coating, followed by firing at 350°C/30 min and high temperature annealing at 750°C/60 min. Both compositional and chemical bonding data were obtained from X-ray Photoelectron Spectroscopy (XPS). XPS analysis shows the presence of carbon impurities only on the film surface. XPS spectra of a pure ZrO 2 film revealed Zr3d 5/2 and 01s peaks, characteristic of fully oxidized Zr atoms. A negligible amount of Sl atoms was detected in the surface region. The deposition of (ZrO 2 )x(Al 2 O 3 ) 1-x films led to the formation of a pseudobinary alloy. The XPS spectra showed a Zr3d 5/2 peak at 183.5 eV and an Al 2p peak at 74.4 eV, attributed to photoemission from the ZrO 2 and Al 2 O 3 , respectively An increased amount of Si atoms in the (ZrO 2 ) x (Al 2 O 3 ) 1-x layers was observed in comparison to the ZrO 2 film.

A simple technique for determination of the diffusion length in a solar cell

Abstract: The surface photovoltage (SPV) effect is widely used for the determination of the minority carrier diffusion length in semiconductors, particularly in solar cells. We have developed a technique based on SPV measurements using a number of calibrated light emitting diodes as monochromatic sources of different wavelengths (λ). The open circuit photovoltage as function of λ was measured at a constant photon flux. The measurements were carried out on mono- and multi-crystalline silicon solar cells. Goodman's model was used to interpret the data and, values of minority carrier diffusion length were deduced. The effect of the injection level and temperature on the minority carrier diffusion length has also been studied.

Structure analysis of nanostructured TiO2 thin films using transmission electron microscopy

Abstract: The study of TiO 2 thin films obtained by the chemical solution deposition method is reported. The film thickness is 40 nm. An original technique is used for lifting the TiO 2 film from the substrate. The samples are examined by transmission electron micrography (TEM) in the diffraction contrast (bright field image) mode, selected area electron-diffraction imaging and convergent beam electron diffraction imaging. The TiO 2 films are nanocrystalline with random orientations. The size of crystallites depends on the annealing temperature. The form of the nanocrystallites indicates the TiO 2 anatase phase. The TEM images are compared with the results from scanning electron micrography.