Low temperature current transport of Sn-GaAs contacts

We measure low temperature current transport properties of superconducting Sn contacts to pf-GaAs. For contacts alloyed at 450 C, the current-voltage characteristics show a strong dependence on alloying time. The critical temperature of Sn near the superconductor-semiconductor interface decreases from 3.8 to 1.8 K as the alloying time increases from 0 to 120 s. On the other hand, a long-time alloying increases the transparency of the interface. Using the Blonder, Tinkham, and Klapwijk model [Phys. Rev. B 25,45 15 ( 1982)], we find that the transmission coefficient of the interface increases from 0.2 to 0.7 by alloying. However, the normal state resistance calculated using the model is much smaller than the experimental value.