Regensburg 2010 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 62: Poster II: Photovoltaics and Organic Semiconductors
HL 62.24: Poster
Thursday, March 25, 2010, 18:00–20:00, Poster D2
Transmission electron microscopy analyses of binary and ternary iron silicides in the system Al:Fe:Si — •Patrick Schwager, Doaa Abdelbarey, and Michael Seibt — Georg-August-Universität Göttingen, IV. Physikalisches Institut, Friedrich-Hund-Platz 1, 37077 Göttingen
In order to use low-cost multicrystalline silicon for photovoltaic applications it is essential to eliminate metal impurities. One technique to remove device-degrading impurities is aluminum gettering which exploits segregation of metal impurities into the forming Al:Si liquid for annealing above the eutectic temperature of 577∘C. The segregation coefficient can be estimated by consulting the binary Al:M and Si:M phase diagrams where M is the metal impurity, here Fe. Experimental data yield instead values which are lower by two orders of magnitude. It has been proposed that this discrepancy stems from a higher solubility of Fe in Si in equilibrium with the ternary Al-doped α−FeSi2:Al compared to that in equilibrium with the binary α−FeSi2 (D.Abdelbarey et al., Appl. Phys. Lett. 94, 061912 (2009)). Due to the slow Al diffusion in Si, the solution of iron in silicon in equilibrium with a α−FeSi2:Al surface layer would be unstable against precipitation into α−FeSi2. In this work, we use transmission electron microscopy techniques to analyze the structure and chemistry of ternary Al:Fe:Si surface layers after high temperature formation as well as extended defects formed in the bulk of the wafers.