Reverse surface photovoltaic effects in GaAs surface quantum wells

We observed that GaAs surface quantum wells on undoped AlGaAs substrates experienced a reverse surface photovoltage (RSPV) that caused the bands to bend upward when illuminated by femtosecond laser pulses for time-resolved two-photon photoemission spectroscopy (TRPES). The RSPV effect is created by trapping of photoexcited electrons in the quantum well. Secondary illumination creates a surface photovoltage opposite in magnitude that flattens the bands. The secondary illumination does not affect the width of the energy spectrum or the ultrafast dynamics with respect to the conduction band minimum. A simple model based on the recombination current from the AlGaAs fits the data excellently.