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 into 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.