Femtosecond time-resolved core-level photoelectron spectroscopy tracking surface photovoltage transients on p-GaAs

Visible-pump/extreme ultraviolet (EUV)-probe spectroscopy using spectrally selected high harmonics of intense laser pulses is utilised for tracking the charge carrier dynamics on semiconductor surfaces. The time evolution of the electric field in the surface layer of p-GaAs(100) is probed with 70 eV femtosecond EUV pulses by measuring the kinetic-energy shifts of Ga-3d core-level photoelectrons after excitation with 3.1 eV femtosecond laser pulses. The observed transient changes of the surface photovoltage reveal carrier transport from the bulk to the surface to occur within 500 fs after photoexcitation, while a subsequent relaxation is determined to evolve on a time scale of a few tens of picoseconds.