Femtosecond laser diagnostics of the built-in electric field across the p+-Si/SiO2 interface and its ultrafast shielding

Ultrafast shielding of the built-in electric field E0 across the p+-Si/SiO interface of boron doped Si upon near infrared femtosecond (fs) laser pulse irradiation (73fs, 35GW/cm2 < Ipeak < 115 GW/cm 2) is shown to be dominated by electron-hole (e-h) pairs generated via twophotonabsorption (TPA), whereas contributions from one-photon absorption (OPA) appear negligible. E0 shows up in the instantaneous signal I of the Electric Field Induced Second Harmonic (EFISH). Its power law is derived from the linear log - log plots of six fs laser wavelengths 741.2 nm < 801.0 nm for the first time. These reveal 1.2 < n(lambda) < 2.1 with the minimum at lambda=752.4 nm (2h*nue =3.3 eV) related to resonantly enhanced TPA. Shielding of E0 by e-h pairs from OPA cannot be detected by EFISH in the same fs laser pulse as their generation requires relatively slow electron-phonon coupling.