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Freiberg, Germany

Stockmeier L.,Fraunhofer Institute for Integrated Systems and Device Technology | Muller G.,Fraunhofer Institute for Integrated Systems and Device Technology | Seidl A.,Schott AG | Lehmann T.,Fraunhofer THM | And 2 more authors.
Journal of Crystal Growth | Year: 2014

Silicon ribbons for photovoltaic applications grown under typical industrial processing conditions by the String Ribbon and the Edge-defined Film-fed Growth (EFG) methods were quantitatively analyzed by newly developed scanning technologies with respect to the grain structure and orientation. As a result the grain structure consists typically of elongated grains with a 〈2 1 1〉 orientation nearly parallel to the growth direction and a {1 1 0} ribbon surface. These grains are mainly separated by Σ3 twin boundaries which are nearly perpendicular to the {1 1 0} ribbon surface. This result is found to be independent from the orientation of seed crystals and is in agreement with earlier studies on silicon ribbon growth. The experimental observations will be explained by a growth model which considers the surface energies of the growing grains and the need for undercooling in front of the phase boundary. © 2014 Elsevier B.V. Source

Reimann C.,Fraunhofer Institute for Integrated Systems and Device Technology | Trempa M.,Fraunhofer Institute for Integrated Systems and Device Technology | Lehmann T.,Fraunhofer THM | Rosshirt K.,Fraunhofer Institute for Integrated Systems and Device Technology | And 4 more authors.
Journal of Crystal Growth | Year: 2016

Different silicon feedstock materials, Single Crystalline Crushed (SCS), Fluidized-Bed-Reactor (FBR) and Siemens (SIE) feedstock, were used as seeding layer for growing cylindrical shaped, high performance multi-crystalline ingots with a weight of 1.2 kg. Within the investigations a systematic variation of the particle size of the seeding material in the range of <1 mm up to 15 mm was performed. Grain size, grain orientation, and grain boundary type were evaluated at different ingot heights. These results show clearly, that the microstructure size, respectively the particle size for the crushed single crystalline material, determines the resulting grain structure in the ingot near the seeding position. If the microstructure size is equal to the particle size, as it is the case for the SCS material, the particle size has a significant influence on grain size, grain orientation, and grain boundary distribution. With increasing average particle size of the SCS seed material the grain size increases, the grain orientation distribution becomes less uniform, and the random grain boundary length fraction decreases. If the microstructure size is smaller than the particle size, as it is the case for FBR and SIE feedstock materials, the particle size has no influence on the initial grain structure of the ingot. For FBR and SIE seeding material, small grains, with a homogeneous orientation distribution and a high random grain boundary length fraction are obtained. Therefore, all FBR and all SIE seeding materials, as well as the SCS with particle size <1 mm, show lowest fractions of defected areas at about the same level which were determined by etch pit analysis. © 2015 Elsevier B.V. Source

Karzel P.,University of Konstanz | Ackermann M.,University of Konstanz | Groner L.,University of Konstanz | Reimann C.,Fraunhofer Institute for Integrated Systems and Device Technology | And 5 more authors.
Journal of Applied Physics | Year: 2013

This investigation analyzes the dependency of minority charge carrier lifetime values at grain boundaries in multicrystalline silicon on the grain boundary type after P gettering and/or firing of SiNx:H layers deposited by plasma enhanced chemical vapor deposition. To get a broad statistics, a new method to determine the coincidence site lattice grain boundary types on large scale throughout entire 50 × 50 mm2 samples is combined with spatially resolved lifetime-calibrated photoluminescence measurements and mappings of the interstitial iron concentration. As an evaluation of the lifetime data at grain boundaries in comparison to the recombination activity of the bordering grains, lifetime contrast values are calculated. The correlation of this dependency on the grain boundary type with the impurity concentration is analyzed by the investigation of multicrystalline samples from two different ingots grown by directional solidification with different crucible material qualities. A dependency of the efficacy of all applied processes on the grain boundary type is shown based on broad statistics-higher coincidence site lattice indexes correlate with a decrease of median lifetime values after all processes. Hydrogenation of both grains and grain boundaries is found to be more effective in cleaner samples. Extended getter sinks, as a P emitter, are also beneficial to the efficacy of hydrogenation. The lifetime contrast values are dependent on the degree of contamination of the multicrystalline silicon material. In cleaner samples, they rather decrease after the processes; in standard solar-grade material, they increase after POCl3 diffusion and decrease again after subsequent hydrogenation. No correlation with the interstitial iron concentration is found. © 2013 AIP Publishing LLC. Source

Dadzis K.,Solar World Innovations GmbH | Niemietz K.,TU Bergakademie Freiberg | Patzold O.,TU Bergakademie Freiberg | Wunderwald U.,Fraunhofer THM | And 2 more authors.
Journal of Crystal Growth | Year: 2013

A new experimental setup containing a GaInSn melt with a square horizontal cross section of 10×10 cm2 and a variable melt height up to 10 cm has been developed. The melt is positioned in the center of a coil system generating a traveling magnetic field (TMF). Using a cooling system at the bottom and a heating system at the top of the melt, a vertical temperature difference up to approximately 50 K can be applied to the melt, imitating the thermal conditions during the directional solidification of multicrystalline silicon. Direct measurements of the time-dependent velocity and the temperature profiles were performed using ultrasonic Doppler velocimetry and thermocouples, respectively. Complementary three-dimensional (3D) numerical simulations of the model experiments were used to validate the numerical tools and to gain a deeper insight into the characteristics of TMF flows in square melts. The classical toroidal flow structure known from isothermal cylindrical melts is shown to obtain a large horizontal central vortex at a small height of the square melt, whereas a distinct 3D asymmetry appears at a large height. A vertical temperature gradient tends to suppress the vertical melt motion and leads to new complex horizontal flow structures. © 2013 Elsevier B.V. Source

Stockmeier L.,Fraunhofer THM | Elsayed M.,Martin Luther University of Halle Wittenberg | Elsayed M.,Minia University | Krause-Rehberg R.,Martin Luther University of Halle Wittenberg | And 4 more authors.
Solid State Phenomena | Year: 2016

To determine the electrically inactive fraction of As or P in heavily doped as-grown Czochralski Si4-point resistivity and SIMS measurements were carried out. No clear trend for the electricalinactive fraction was found with an increasing dopant concentration, though a mean electricalinactive fraction of 11.5% for As doping could be determined.Experimental results on a dopant-vacancy complex in as-grown Si are scarce, hence temperature dependentpositron annihilation lifetime spectroscopy (PALS) was carried out on several heavily Asand P doped as-grown Si samples. The measured average positron annihilation lifetime τav isbetween 218 ps and 220 ps. No temperature dependent effect on τav could be observed. Therefore, itcan be concluded that in the studied doping range the dopant-vacancy complexes do not exist. Thereason for the inactivation of the dopant has to be found elsewhere. A possible explanation can bethe formation of dopant precipitates. © (2016) Trans Tech Publications, Switzerland. Source

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