Gate-voltage dependence of the critical current of the superconducting field effect transistor

The saturation of the critical current as a function of the gate voltage found in the Nb-Si-Nb superconducting field effect transistor is analyzed numerically using the de Gennes expression for the proximity effect. According to the analysis, (i) the Schottky barrier effect is found to be negligible under experimental conditions, (ii) mobility of silicon fitted to the experimental curve shows a power relation to the gate voltage with exponent of about −0.81. This exponent is consistent with the results from independent experiments and a simple theory of surface scattering. The results indicate that the surface scattering effect causes the saturation phenomenon.