Investigation of Fermi-level pinning at silicon/porous-silicon interface by vibrating capacitor and surface photovoltage measurements

In this paper the PSi–silicon interface properties have been investigated by surface photovoltage (SPV) and vibrating capacitor (Kelvin) measurements. These methods are sensitive for the work function change and for the PSi–silicon interface potential barrier. The porous silicon (PSi) layer contains huge number of volume traps. Theoretical considerations support the high band bending (near to intrinsic condition or inversion) at the PSi–silicon interface, as high charge carrier concentration at the interface would result in high charge injection into the porous silicon. SPVand vibrating capacitor experiments show that the PSi volume charge and PSi–silicon interface charge tends to shift the interface to depleted state, near to the intrinsic condition (Fermi-level pinning). The interface conditions are summarised in the article and compared with the surface properties of the earlier discussed silicon-dioxide-covered silicon system. Light excitation can affect the charge stored in the PSi, thus the potential barrier at the PSi–silicon interface: the light induced surface voltage transients reveal this charge injection effect.