Combined electron-hole dynamics at UV-irradiated ultrathin Si-SiO₂ interfaces probed by second harmonic generation

UV irradiation of ultrathin SiO₂ on Si can lead to injection of both holes and electrons into the oxide. 4.9-eV photons lead to electron injection while 6.7-eV photons open up the hole injection channel. The holes and electrons can trap, generating electric fields of opposite signs. Second harmonic generation (SHG) is sensitive to both the sign and magnitude of the electric field at the buried interface, revealed by opposing electric field induced second harmonic (EFISH) generation contributions. The SHG response of UV-irradiated Si-SiO₂ slowly evolves to the SHG pattern characteristic for unirradiated Si-SiO₂. We attribute the phenomenon to combined dynamics of electrons and holes at the Si-SiO₂ interface.