A solid-state diffusion theory is developed giving the distribution of impurities in epitaxial growth. It is shown that for most practical cases this theory takes on a particularly simple form. Extensive experiments were performed in the study of the distribution of the most common acceptor and donor type substrate impurities in silicon: boron and antimony. It is shown that the impurity distribution in most of the epitaxial film is uniform corresponding to the impurity doping of the SiCl4 used in the epitaxial growth, and that the profile near the substrate—film interface is very close to the predictions of this simple theory. In addition, certain particular cases of interest were studied such as the spreading of a layer of impurities predeposited on the substrate surface prior to epitaxial growth, the effect of film growth rate on the impurity distribution, and the change in the impurity distribution during an additional high-temperature step. In all cases, experiments and the solid-state diffusion theory are in excellent agreement.

No abstract

No abstract

The influence of the milling liquid on the properties of donor-doped ( La3+) semiconducting barium titanate ( BaTiO 3 ) ceramics, generated by the mixed oxide technique, was investigated. Distilled water and propan-2-ol were used as milling liquids. Water was found to have two essential effects. First, it dissolves Ba2+ ions out of BaTiO 3 grains, thus creating core-shell structures which were confirmed by high-resolution electron microscopy ( HREM) and electron energy loss spectroscopy ( EELS). They consist of a 3-5 nm thick TiO x -rich layer followed by a layer (ca. 10 nm thick) with a molar Ba/Ti ratio increasing from 0 to 1. These core-shell structures of the BaTiO 3 powder positively affect the sintering behaviour of the greens by the high reactivity of the Ti-rich interlayer. Secondly, water cleans the BaTiO 3 powder of acceptor contaminants, producing ceramics with a low electrical resistivity at room temperature. Propan-2-ol-milled ceramics of a comparable composition show an electrical resistivity up to six orders of magnitude higher, owing to the compensation of La3+-doping by acceptor contaminants.

A new procedure for the preparation of a core-shell-structured BaTiO(3) precursor (core=TiO(2); shell=BaCO(3)) will be described. The structure of this precursor is characterized by electron microscopy (environmental scanning electron microscopy; energy disperse X-ray spectroscopy), whereas the development of phases during thermal treatment is followed by X-ray powder diffraction.