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Transmission electron microscopy based interface analysis of the origin of the variation in surface recombination of silicon for different surface preparation methods and passivation materials

: Ali, H.; Moldovan, A.; Mack, S.; Schoenfeld, W.V.; Davis, K.O.


Physica status solidi. A 214 (2017), No.10, Art. 1700286, 4 pp.
ISSN: 0031-8965
ISSN: 1862-6300
ISSN: 1521-396X
ISSN: 1862-6319
Journal Article
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Photovoltaik; Silicium-Photovoltaik; Oberflächen: Konditionierung; Passivierung; Lichteinfang; cleaning; silicon; analysis; passivation; electron microscopy

In this work, the root cause of variation in surface recombination for Si wafers after different cleaning processes and for different passivation layers is investigated using a combination of calibrated photoluminescence (PL) imaging and transmission electron microscopy (TEM). The use of a HF-last or oxide-last cleaning and/or conditioning process is shown to have a strong impact on surface recombination for SiNx passivated surfaces, but little impact for Al2O3/SiNx stacks. For a SiNx passivation layer, cross-sectional TEM imaging revealed the formation of a â1-2nm SiOx interlayer resulting from a controlled oxidation during the last cleaning/conditioning step. The presence of the SiOx layer reduces the interface defect density (Dit,midgap) by an order of magnitude and dramatically increases the effective carrier lifetime. However, for Al2O3/SiNx passivated surfaces, TEM studies revealed that a SiOx layer is formed at the interface between the c-Si and AlOx even for c leaning processes ending with HF-last treatment due to which the cleaning sequence has minimal impact on the effective carrier lifetime.