CRITICAL CURRENTS AND SUPERCURRENT OSCILLATIONS IN JOSEPHSON FIELD-EFFECT TRANSISTORS

The dc Josephson effect of a superconductor/two-dimensional electron g as/superconductor (S/2DEG/S) junction in the clean limit is investigat ed with emphasis on the field-effect dependence of the critical curren t. Calculation of the Josephson current is based on solving the Bogoli ubov-de Gennes equations for a steplike variation of the pair potentia l. In the normal conducting region, the motion of electrons is quantiz ed in one direction by means of a triangular-well potential. The 2DEG is contained in a semiconductor treated within the effective-mass appr oximation. We assume an abrupt band-edge jump at the interfaces, and a dditional scattering is taken into account by delta-function potential barriers. Normal scattering leads to the formation of resonant states , which are visible in critical current oscillations. The ratio of Fer mi velocities in the 2DEG and the S regions determines the rates of An dreev and normal scattering and has a large influence on the field-eff ect dependence of the critical current. We take an effective mass suit able for the inversion layer on p-type InAs and consider Nb for the su perconducting contacts. Typical magnitudes of the calculated critical current are some muA-per-mum junction width for experimentally accessi ble values of junction length, temperature, and surface carrier densit y of the 2DEG.