Semiconductor heterostructure weak links for Josephson and superconducting FET applications

Superconductor-normal-superconductor (SNS) weak links using a semiconductor as the normal region are of interest for applications in high frequency Josephson devices and in superconducting field effect transistors. Recently, there has been a revival of interest in materials such as InAs which, in principle, allow true SNS structures without tunneling (Schottky) barriers at the electrodes, In this paper we discuss the requirements for semiconductor SNS Josephson and FET devices and describe the fabrication and characterization of planar SNS weak links in which the normal region is InAs, which is part of a heterostructure consisting of a thin (100 nm) layer of n-InAs grown on undoped GaAs. Nb electrodes defined by electron beam lithography have been made with spacings as small as 260 nm. Preliminary measurements indicate that the devices have good electrical behavior which is well explained by SNS weak link theory, using coherence lengths calculated from measured material parameters. These weak links can be the basis for superconducting FET devices, and have the significant advantage of allowing simple device isolation compared with bulk InAs, which was used in earlier work.