Surface state capture cross sections at Si/electrolyte interfaces determined by combined microwave reflection/photocurrent measurements

Abstract

The change in reflected microwave power due to the photoinduced change of the sample's average conductivity is measured. The resulting microwave reflection signal is proportional to the change of the integral over the excess carrier profile in the semiconductor sample. With a relation between this profile and the excess charge carrier concentration at the surface, the measured change in reflected microwave power is a measure for the change in surface concentration of excess carriers. With this link simultaneously recorded microwave reflection signal and photocurrent are combined to separate the surface recombination velocity from the charge transfer constant using a model for the microwave reflection signal containing these two parameters explicitly. For n-Si (4–5 × 10¹⁴ cm⁻³) in contact with dried propylene carbonate (PC) containing 0.1 M tetrabutylammonium perchlorate (TBAP) and 10 mM ferrocene/ferrocenium, these two quantities are measured under periodic illumination as a function of the applied potential. The approximation of the separated surface recombination velocity with a potential dependent Shockley–Read–Hall-formalism yields the capture cross sections for electrons (4 × 10⁻¹⁶ cm³s⁻¹) and holes (4 × 10⁻¹⁸cm³s⁻¹) of the relevant surface recombination levels.