Gate-Controlled Superconductor/Two-Dimensional-Electron-Gas Junctions

Abstract

Compared with metals, semiconductors have the great advantage that the electron concentration can be changed very easily by means of a gate electrode. As we discussed in the preceding chapter, where light exposure was employed, a change of the electron concentration has an immediate effect on the superconducting properties, i.e. the critical current. The first structure discussed below, which utilizes this effect, is the Josephson field effect transistor (JoFET). This is a three-terminal device; the supercurrent of the superconductor/semiconductor Josephson junction can be switched on and off by applying a gate voltage. Besides questions related to the JoFET, which might be used in future electronic circuits, some more fundamental questions related to the wave nature of the particles can also be addressed by studying superconductor/semiconductor structures controlled by a gate. Typical examples, which will be discussed below, are interference effects due to Fabry—Pérot resonances, fluctuation and localization effects, and the quantization of the critical current.