Molecular field effect passivation: Quinhydrone/methanol treatment of n-Si(100)

The quinhydrone/methanol treatment has been reported to yield outstanding passivation of the H-terminated Si(100) surface. Here, we report on the mechanism of this process by comparing the resulting surface to that of freshly etched H-terminated Si, of Si with chemically grown oxide, and of Si treated with hydroquinone/methanol solution of the same concentration. We find that the benzoquinone moieties of the quinhydrone react with the surface to yield a Si-hydroquinone surface termination, while the methanol molecules bind as well to form methoxy-terminated Si. The slightly negative-charged benzene ring of the hydroquinone acts to repel majority carrier electrons from the surface and inhabits the surface recombination. The higher the ratio of surface-bound hydroquinone to surface-bound methoxy species, the larger the minority carrier life-time measured by microwave photoconductivity. Thus, our results lead us to conclude that this treatment results in field effect passivation; remarkably, this effect is caused by a molecular monolayer alone.