Proximity-effect superconductive tunneling in Nb on InGaAs/InP/InGaAs heterostructures

We present experimental data on proximity tunneling in InGaAs/InP/InGaAs heterostructures due to a Nb film which induces superconductivity in the top InGaAs layer. The proximity effect is demonstrated in tunneling measurements yielding superconducting parameters induced in the top InGaAs layer, such as the gap, Δ, the tunneling density of states, D(E), and their variations with the temperature, T. We observe a significant smearing of D(E). This is attributed to a spatial decay of the gap into the depth of the InGaAs layer. Superconductivity in InGaAs is also directly evidenced through measurements of the lateral current using a sequence of Au-Nb-Au pads on InGaAs.