An investigation of electronic passivation of silicon <100> surfaces in solutions of p-benzoquinone

Costello, Luke
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University of Delaware
Silicon <100> surfaces under passivation by p-benzoquinone/methanol solu- tions have shown significant increases in minority carrier lifetime relative to hydrogen terminated surfaces. This appears to be a good candidate system for future improvements to existing Si solar technologies but little is known about the physical mechanism of passivation. The following work focuses on three areas; the importance of solvent choice in the observed passivation effect, passivation of surfaces with thin native oxides, and analysis of surface coverage and composition using X-ray Photoelectron Spectroscopy (XPS). Previous studies have largely ignored solvent choice, primarily using methanol. It is shown that on Si <100> surfaces using methanol as a solvent provides higher minority carrier lifetimes while also reaching plateau values more quickly than solutions with diethyl ether as the solvent. Next oxidized wafers are investigated. A wafer with native oxide of roughly 2 nm shows a significant increase in minority carrier lifetime when immersed in solutions of p-benzoquinone/methanol. When the native oxide layer is 22 nm thick however there is no observed passivation effect. Lastly a surface analysis of Si <100> wafers out of the box (native oxide on the surface), after etching with piranha and HF (hydrogen terminated surface), after 1 hour in methanol, after 1 hour in p-benzoquinone/methanol, and after 1 hour in hydroquinone/methanol was done by XPS. The p-benzoquinone and methanol treated surfaces show signs of Si-O bonding however the peak heights after the 1 hour period are too small to be conclusive. We conclude that there is insufficient surface coverage to provide sufficient signal strength.