Browsing by Author "Rudolf, C."

Co-precipitation of copper and nickel in silicon bicrystals produced by wafer-bonding has been investigated. Transmission electron microscopy and energy-dispersive X-ray analysis show two types of precipitates: copper-rich silicide particles that contain a small partial mole fraction of 5% of nickel and nickel-rich particles containing a partial mole fraction between 15% and 25% of copper. Both types of precipitates are found inside large precipitate colonies typical for copper precipitation in silicon in the absence of nickel co-doping. Thermodynamically these precipitates can be assigned to the known binary metal silicide phases Cu(3)Si and NiSi(2) and a solid Solution of a second metal species therein. (C) 2008 Elsevier B.V. All rights reserved.

Three kinds of Co-rich magnetic amorphous films of CoFeB, CoFeNiSiB, and CoFeHfO were prepared by magnetron sputtering and applied as soft ferromagnetic (FM) electrodes in tunneling magnetoresistance (TMR) devices. Initial results exhibit a large room-temperature TMR effect of approximately 50%. The high effect can be attributed to interfacial coherence between the amorphous barrier-electrode layers and, accordingly, suggests a high local spin polarization possibly associated with strong nearest-neighbor spin correlations of the magnetic atoms. The magnetotransport behavior may be governed by details of the local spin environment in magnetic amorphous electrodes due to their short electron mean-free path (similar to 3-5 angstrom). The annealing effect on TMR was found to be more pronounced due to the atomic cooperative structural relaxation and more thermally stable compared with the polycrystalline electrode junctions. Additionally, the use of the magnetic oxide electrode CoFeHfO has shown that the relevant FM electrode-barrier interface becomes insensitive to the oxygen, which simplifies the oxidation process used for the oxide barrier fabrication.

This paper summarizes current understanding and predictive simulations of gettering processes predominantly applied in silicon photovoltaics. Special emphasis is put on various processes limiting gettering efficiency and kinetics, i.e. the mobility of interstitially dissolved metal species, the formation of the gettering layer, and the effect of immobile metal species. The latter are substitutional metal species, precipitates, complexes with defects related to non-metallic impurities, and finally the interaction with extended defects, in particular dislocations. Finally, alternative annealing schemes involving high-temperature rapid thermal processing are explored by simulations. It is shown that a processing window exists for a two-step process efficient for the removal of precipitates even under the constraints of a fixed thermal budget for phosphor-us diffusion. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multicrystalline silicon materials for photovoltaic applications inherently contain extended defects like grain boundaries, dislocations. microdefects and in some cases also second phase precipitates due to high concentrations of light elements (carbon, nitrogen or oxygen) and transition metal impurities. The latter are known to reduce the minority carrier lifetime and hence should be removed by gettering during solar cell processing. This paper discusses the influence of extended defects on the spatial distribution of copper- and nickel-related silicide precipitates for a model system containing a small angle grain boundary and in one part silicon oxide pecipitates partly associated with punched-out dislocations. Phosphorus-diffusion gettering under conditions of mostly precipitated metal impurities is discussed in terms of quantitative simulations. It is shown that two regimes can be distinguished where gettering kinetics are either limited by precipitate dissolution or phosphorus in-diffusion. Finally, binding of metal impurities to dislocations is considered and its effect on gettering kinetics is illustrated in terms of gettering simulations. (c) 2009 Elsevier B.V. All rights reserved.

We report temperature-dependent LBIC-measurements on copper-nickel co-diffused Czochralski-silicon bicrystals focussing on the distribution and the recombination properties of the metal-precipitated defects. The samples had been hydrophobically wafer-bonded from two n-type materials with slightly different doping concentration and thermal history. LBIC analyses in cross-section geometry reveal substantially different spatial distributions of metal-related precipitates between the two crystals. This behaviour is explained by oxygen-related microdefects present in one wafer, acting as efficient nucleation sites. A precipitate-free zone was found below the surface but not beneath the bonding interface. At isolated colonies LBIC contrasts in the range of 50% have been observed indicating strong carrier recombination at such defects. (c) 2008 Elsevier B.V. All rights reserved.