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Kamrla, Robin, Tr├╝tzschler, Andreas, Huth, Michael, Chiang, Cheng-Tien, Schumann, Frank O., Widdra, Wolf

SiO2/Si(001) studied by time-resolved valence band photoemission at MHz repetition rates: Linear and nonlinear excitation of surface photovoltage
Journal of Vacuum Science & Technology A 37, (2),pp 021101/1-6 (2019)
The authors investigate the fluence and doping dependence of the surface photovoltage (SPV) shifts at SiO2/Si(001) interfaces by time-resolved photoelectron spectroscopy. Charge carriers are excited by pumping photon energies of hνpump = 1.2 and 2.4 eV and probed by high-order harmonics of hνprobe = 22.6 eV at 0.2 and 0.7 MHz repetition rates. The authors observe SPV shifts of the non-bonding O2p state by 240 meV for SiO2/p-Si and by -140 meV for SiO2/n-Si upon pumping with hνpump = 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.