Vida Kazlauskiene

New sterically hindered Hf, Zr and Y β-diketonates as MOCVD precursors for oxide films

New Zr, Hf and Y 2,7,7-trimethyl-3,5-octanedionates (tod) as well as the corresponding Cu β-diketonate have been synthesized and characterized by FT-IR, elemental analyses, TGA, and 1H NMR or ESR. The molecular structure of Hf(tod)4 has been determined by single-crystal X-ray diffraction, the metal displays a square antiprismatic geometry. Zr, Hf and Y β-diketonates were investigated as precursors for MOCVD deposition of ZrO2, HfO2 and yttria-stabilized hafnia thin films. The films were characterized by XRD, XPS, EDS and AFM. Highly textured and in-plane oriented films were deposited on sapphire by pulsed liquid injection MOCVD. Zr(tod)4 and Hf(tod)4 precursors lead to higher growth rates of ZrO2 and HfO2 films at lower temperatures than conventional Zr(thd)4 and Hf(thd)4 precursors (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) and are attractive new precursors for oxide films.

The influence of crystallite and interface region properties on the CdSe layer photoconductivity

Abstract The CdSe polycrystalline layer was analyzed by means of ESCA, SIMS, photoconductivity and Hall effect methods, and surface and bulk phenomena were researched. The activation of photoconductivity during the thermal treatment in air with and without CdCl 2 was investigated. It was found that the oxide formation decreased, if the chlorine was in the ambient, which caused the achievement of a higher compensation level. The prevalence of Cd or Se vacancies in the formation determined the conductivity and photosensitivity of the polycrystalline layer. Thermal quenching, persistent conductivity and the percolation regime at low temperatures were analyzed as well.

Synthesis and characterization of Li1/3Ce2/3PO4 and LiCe2/3PO4 ceramics

Li1/3Ce2/3PO4 and LiCe2/3PO4 compounds were synthesized by a solid state reaction and studied by x-ray diffraction and thermogravimetric analysis. At room temperature the investigated compounds exhibit monoclinic symmetry (space group P 21/n) with four formula units in the lattice. The compounds are stable up to 1200 K in air and show no weight loss. The ceramic samples were fabricated with varying sintering times. The surfaces of the ceramics were studied by scanning electron microscopy. The increase of sintering time of the ceramics leads to an increase of the grain size of the materials. The results of an x-ray photoelectron spectroscopy study have shown that the external electric field changes the Li amount on the surfaces of the ceramic samples. The electric properties of the samples were investigated by complex impedance spectroscopy in the frequency range from 50 to 1.2 × 109 Hz in the temperature range from 300 to 650 K. Varying the sintering time of the ceramics affects the values of the total conductivity, activation energy, dielectric permittivity and dielectric losses of the ceramics.

Self-organized nanoclusters of semiconductor compounds on vicinal Si surfaces and its influence on carrier recombination in Si

Abstract The self-organized nanocluster ensembles of ZnSe, CdSe and PbS were grown by laser ablation on vicinal Silicon (111) surfaces. The properties of the layers were investigated by XPS (X-rays photoelectron spectroscopy) and Auger spectroscopy. The properties of the semiconductor-clustered layer on single Si crystal structure were investigated by deep level transient spectroscopy (DLTS) and by microwave absorption induced by light pulse excitation. The clustered layer and multilayer structure modified the recombination at the Si surface and created additional carrier capture centres. Absolute values of surface recombination rate, s, were determined by the method of asymptotic lifetime amplitude. An increase of s is caused by formation of PbS clusters, while for CdSe clusters, this dependence was found to be weaker. Structures with barriers or flat conduction bands were grown on the silicon surface using different doping concentrations of layers.