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

In a highly doped GaAs semiconductor with superconducting contacts of Al, clear conductance peaks are observed at zero voltage bias and at V0ex0ex=0ex0ex±2Δ/e, ±Δ/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.