Interplay between negative photoconductivity and enhanced Andreev reflection in InGaAs-based S-Sm-S junctions when exposed to infrared light

We investigated the transport properties of an S-Sm-S junction with a two-dimensional electron gas (2DEG) in an In_0.52Al_0.48As/In_0.7Ga_0.3As heterostructure when exposed to light from infrared laser diodes. When the sample was illuminated with λ = 1.3 μm, we observed a reduction in the junction resistance as well as an enhancement of Andreev reflection. In contrast, we observed negative photoconductivity owing to a reduction in the number of electrons in the 2DEG when it was exposed to 1.3 μm light, by employing both Shubnikov-de Haas and Hall-effect measurements. These experimental results indicate that the improvement in the superconducting properties does not originate from the photo-induced carriers in the 2DEG but from the increase in the Andreev reflection probability at the S/Sm interface caused by lowering the interface barrier.