Multiple Andreev reflections in ballistic Nb-InGaAs/InP-Nb junctions

The current-voltage characteristics of ballistic Nb-InGaAs/InP-Nb Josephson junctions have been investigated. At temperatures below 1 K a negative dif ferential conductance, which usually leads to a hysteresis in the current-v oltage characteristics, was resolved by connecting an additional external s hunt resistor to the junction. The negative differential conductance is exp lained by heating and conductance enhancement due to multiple Andreev refle ctions. The structures observed in the differential resistance measurements as a function of the bias voltage are explained by self-detection of Josep hson radiation at low bias voltages and subharmonic gap structures at highe r bias voltages. (C) 1999 Academic Press.