In this work we present a study of a p-type Czochralski-grown Si ingot which was grown using 10% solar grade silicon ͑SoG-Si͒. As the SoG-Si contains a relatively high concentration of impurities including phosphorus, the electrical properties of the as-grown wafers from this ingot are affected by both the compensating dopants and other impurities. Measurements of the minority charge carrier lifetime in the as-grown material reveal very low values ͑4-8 s͒. The Hall mobilities at room temperature correspond to normal values for Czochralski silicon in the upper part of the ingot ͑which solidifies first͒ and decrease significantly toward the bottom of the ingot. Segregation leads to an accumulation of impurities toward the lower parts of the ingot as well as to a stronger increase in phosphorus than of boron, the latter of which results in a high compensation level ͑i.e., an increasing resistivity͒. A priori, both effects could be responsible for the degradation of the electrical properties in the lower parts of the ingot, whereas theoretical considerations show that the level of compensation should not cause a strong decrease in Hall mobility at room temperature. Untextured solar cells have been processed from wafers originating from different positions of the ingot. As expected, the phosphorus diffusion leads to a gettering effect: the recombination active impurities are removed out of the wafer volume. This results in relatively high efficiencies ͑Ͼ16% ͒ of the solar cells but does not show a strong correlation between ingot height and cell efficiency. This observation is also confirmed by the high bulk lifetimes ͑Ͼ200 s͒ measured after the process even for samples originating from the last solidified ͑lower͒part of the ingot. The Hall mobility of samples cut from finished solar cells has been measured and shows the same trend as the as-grown samples, the values for the bottom of the ingot still being very low. With the concentrations of boron and phosphorus studied up to this point, compensation showed no detrimental effect on the cell efficiency of industrial-like solar cells.
This paper investigates the impact of iron (Fe) and molybdenum (Mo) when they are introduced in the feedstock for mono- and multicrystalline Float-Zone (FZ) silicon (Si) growth. Neutron Activation Analysis shows that the segregation coefficient is in agreement with literature values. Lifetime maps on monocrystalline wafers show a uniform lifetime which decreases with the increase of contamination levels. Multicrystalline wafers show low lifetime areas, corresponding to grain boundaries and highly dislocated areas, which are independent from the contamination levels. Intra grain areas have a higher lifetime which changes with the contamination levels. The solar cells show a reduced diffusion length in multicrystalline uncontaminated cells compare to the monocrystalline uncontaminated. In multicrystalline cells the lowest level of Fe introduced (1012 atm/cm3) has hardly any influence, whereas in the Mo-contaminated cells the impact is visible from the lowest level (1011 atm/cm3). In monocrystalline cells the diffusion length is reduced already at the lowest contamination level of Fe.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.