Submicron Gate-Fitted Superconducting Junction Using a Two-Dimensional Electron Gas

We fabricated submicron-gate superconducting junctions which are coupled with an InAs channel inserted in an InAlAs/InGaAs heterostructure. Electron beam lithography, and chemical and rf sputter etching techniques are used to fabricate a junction in the submicron range. The fabrication process of the junction is described in detail. The fabricated gate configuration shows high controllability of both the superconducting critical current and normal resistance of the junction using gate voltage. This provides a voltage gain of over 1 and enables the first demonstration as a Josephson field effect transistor. Moreover, new quantum phenomena, e.g., Fabry-Pérot interference and quantization of critical current as well as focusing of Andreev-reflected holes in a quantum point contact, were observed. Junction characteristics from the viewpoints of both three-terminal operation and the new quantum phenomena are reported.