Effect of Material Quality on Superconducting Proximity Effect in Al-InAs Heterostructures*

Renewed theoretical and experimental interest in InAs heterostructure with two-dimensional electron systems (2DESs) confined to the surface is partly due to their potential applications in topological and superconducting quantum computation. Here we study Josephson junctions with epitaxial Al-InAs contacts and find large super currents and substantial product of I_CR_N in our high mobility wafers. We also compare the product of excess current and normal resistance, I_exeR_N of high mobility samples and low mobility samples. The excess current is negligible in the devices made of lower mobility Al-InAs samples whereas it is substantial and independent of gate voltages and junction length in high mobility sample. For the devices made with high mobility samples, we found that I_CR_N/Δ~2.2. Further we discuss how the above parameters are linked to the material quality of the samples.