Determination of impurity distributions in ingots of solar grade silicon by neutron activation analysis
AbstractIn a series of crystallization experiments, the directional solidification of silicon was investigated as a low cost path for the production of silicon wafers for solar cells. Instrumental neutron activation analysis was employed to measure the influence of different crystallization parameters on the distribution of 3d-metal impurities of the produced ingots. A theoretical model describing the involved diffusion and segregation processes during the solidification and cooling of the ingots could be verified by the experimental results. By successive etching of the samples after the irradiation, it could be shown that a layer of at least 60 μm of the samples has to be removed to get r…
Behavior of a trapezoid-based data acquisition system up to 100 kHz and beyond
In this work, we investigated the ability of a high-purity germanium detector connected to a trapezoid-filter-based data acquisition system to reliably record signals in spite of high sample activities. By activating multiple Na$_{2}$CO$_{3}$ samples with different Na content, we were able to deduce efficiency, resolution and dead time of the system used as a function of the sample activity. Based on the results, we were able to find a setting which allows measurements of event rates up to 35~kHz per readout channel with an energy resolution of 0.3\% at the 2754 keV $^{24}$Na line.
Improving the material quality of silicon ingots by aluminum gettering during crystal growth
We present a method for the purification of silicon ingots during the crystallization process that reduces significantly the width of the low charge carrier lifetime region at the ingot top. The back-diffusion of impurities from the ingot top is suppressed by adding a small amount of pure aluminum into the silicon melt right at the end of the solidification. We study the aluminum gettering effect by instrumental neutron activation analysis (INAA) and Fei imaging. Furthermore, we present a model for aluminum gettering of Fe in the silicon ingot that is in agreement with literature data for aluminum gettering at lower temperature. The distribution of iron in the ingots with and without alumin…
Thermal neutron capture cross section of the radioactive isotopeFe60
Background: Fifty percent of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections.Purpose: One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as $^{60}\mathrm{Fe}$ with a half-life of $2.60\ifmmode\times\else\texttimes\fi{}{10}^{6}$ yr. To reproduce this $\ensuremath{\gamma}$ activity in the universe, the nucleosynthesis of $^{60}\mathrm{Fe}$ has to be understood reliably.Methods: An $^{60}\mathrm{Fe}$ sample produced at the Paul Scherrer Institut (Villigen, Switzerla…