Electron Photoinjection from Silicon to Ultrathin SiO2Films via Ambient Oxygen

Abstract

Hot electrons are generated in Si(001) at 295 K via linear absorption of $>4.3\mathrm{eV}$ photons or by three-photon processes using 270 fs, 800 nm (1.55 eV) optical pulses. Electron trapping in oxide films is observed via time-dependent optical second harmonic generation induced by the electric field associated with charge transfer. For anodically oxidized samples and constant beam irradiance, the transfer rate decreases to zero with increasing oxide thickness with a characteristic length of 3.5 nm, comparable to the electron scattering length; the rate increases with ambient oxygen pressure ( $P$) as $P^{0.035}$. These results indicate that oxygen is essential to hot electron transfer in ultrathin oxides and serves at least as a trapping catalyst.