Role of inversion layer formation in producing low effective surface recombination velocities at Si/liquid contacts

Abstract

Photoconductivity decay lifetimes have been obtained for NH₄F_(aq)-etched Si(111) and for air-oxidized Si(111) surfaces in contact with solutions of CH₃OH or tetrahydrofuran (THF) containing either ferrocene^(+/0) (Fc^(+/0)), bis(pentamethylcyclopentadienyl) Fe^(+/0), or I₂. Si surfaces in contact with electrolytes having Nernstian redox potentials >0 V versus the standard calomel electrode exhibited low effective surface recombination velocities regardless of the different surface chemistries, whereas those exposed only to N₂(g) ambients or to electrolytes containing mild oxidants showed differing rf photoconductivity decay behavior depending on their different surface chemistry. The data reveal that formation of an inversion layer, and not a reduced density of electrical trap sites on the surface, is primarily responsible for the long charge-carrier lifetimes observed for Si surfaces in contact with CH₃OH or THF electrolytes containing I₂ or Fc^(+/0).

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