0000000000068719
AUTHOR
Stefan Reber
Fast determination of impurities in metallurgical grade silicon for photovoltaics by instrumental neutron activation analysis
Standard wafer solar cells are made of near-semiconductor quality silicon. This high quality material makes up a significant part of the total costs of a solar module. Therefore, new concepts with less expensive so called solar grade silicon directly based on physiochemically upgraded metallurgical grade silicon are investigated. Metallurgical grade silicon contains large amounts of impurities, mainly transition metals like Fe, Cr, Mn, and Co, which degrade the minority carrier lifetime and thus the solar cell efficiency. A major reduction of the transition metal content occurs during the unidirectional crystallization due to the low segregation coefficient between the solid and liquid phas…
Strain induced renormalization of transport properties in UPt3 thin films
The growth of sputter deposited UPt3 thin films on Al2O3 (1012), LaAlO3 (111) and SrTiO3 (111) was investigated. We found strongly 0001-textured growth of UPt3 in a small compositional range of 23–25% uranium content. For Al2O3-and LaAlO3-substrates no in-plane order could be observed whereas epitaxial growth was initiated on SrTiO3 (111): The growth can be identified as Vollmer-Weber like resulting in the formation of large lateral strain as a consequence of the growth mode and a lattice misfit of −4.3% between UPt3 (0001) and SrTiO3 (111). Strong deviations from the typical heavy-fermion characteristics in electronic transport properties like resistivity, magnetoresitivity and Hall-effect…
HCl gas gettering for crystalline silicon thin film solar cells
Crystalline silicon thin film (cSiTF) solar cells could be an attractive alternative for standard silicon solar cells. Only a small amount of the expensive high purity silicon is needed for the epitaxial deposition on a low-cost silicon substrate made from e.g. metallurgical grade (MG) or upgraded metallurgical grade (UMG) silicon. The resulting product is called epitaxial wafer equivalent (EpiWE) because it can be processed in a standard wafer cell production. MG-Si and UMG-Si still contain a huge amount of metallic impurities. These impurities have to be removed by gettering methods in order to prevent diffusion into the highly pure active silicon layer during the high-temperature deposit…
HCl gas gettering of low-cost silicon
HCl gas gettering is a cheap and simple technique to reduce transition metal concentrations in silicon. It is attractive especially for low-cost silicon materials like upgraded metallurgical grade (UMG) silicon, which usually contain 3d transition metals in high concentrations. Etching of silicon by HCl gas occurs during HCl gas gettering above a certain onset temperature. The etching rate as well as the gettering efficiency was experimentally determined as a function of the gettering temperature, using UMG silicon wafers. The activation energy of the etching reaction by HCl gas was calculated from the obtained data. The gettering efficiency was determined by analyzing Ni as a representativ…