Decay Lengths for Diffusive Transport Activated by Andreev Reflections in Al/<i>n</i>-GaAs/Al Superconductor-Semiconductor-Superconductor Junctions

Abstract

In a highly doped GaAs semiconductor with superconducting contacts of Al, clear conductance peaks are observed at zero voltage bias and at $V\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}2\ensuremath{\Delta}/e,$ $\ifmmode\pm\else\textpm\fi{}\ensuremath{\Delta}/e$. The subharmonic energy gap structure originates from Andreev scattering with diffusive, but energy conserving, transport in the GaAs. The zero bias excess conductance is due to phase-coherent transport. Both effects are suppressed when the distance between the superconducting electrodes exceeds the inelastic diffusion length in the GaAs normal channel.