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

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 N_2(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.