Position dependent optical effect on the transport properties of S-Sm-S junctions

We have experimentally investigated the optical effect on the transport properties of superconductor-semiconductorsuperconductor (S-Sm-S) junctions composed of a two-dimensional electron gas in a GaAs/AlGaAs heterostructure and NbN superconducting electrodes. Illumination at λ800nm onto the whole junction area increases Andreev reflection (AR) probability at S-Sm interfaces. To explore this origin, we performed scanning photovoltage measurements by using an optical microscope. The obtained image plots of the photovoltage show that the illumination brings about the photovoltage at the S-Sm interfaces. This result implies that the illumination modulates the barrier height between S and Sm, which results in a modulation of AR probability.