SiO 2/Si(001) studied by time-resolved valence band photoemission at MHz repetition rates: Linear and nonlinear excitation of surface photovoltage

The authors investigate the fluence and doping dependence of the surface photovoltage (SPV) shifts at SiO 2 /Si(001) interfaces by time-resolved photoelectron spectroscopy. Charge carriers are excited by pumping photon energies of h ν p u m p = 1.2 and 2.4 eV and probed by high-order harmonics of h ν p r o b e = 22.6 eV at 0.2 and 0.7 MHz repetition rates. The authors observe SPV shifts of the nonbonding O 2 p state by 240 meV for SiO 2 / p-Si and by − 140 meV for SiO 2 / n-Si upon pumping with h ν p u m p = 1.2 eV, and their decay rate is estimated from time-resolved measurements. Moreover, the authors observe a striking pumping fluence dependence of SPV at these interfaces, which indicates charge carrier generation by both linear and nonlinear optical excitations.