  Hyperdoping with gallium (Ga) has been established as a route to observe
superconductivity in silicon (Si). The relatively large critical temperatures
(T$_{\rm c}$) and magnetic fields (B$_{\rm c}$) make this phase attractive for
cryogenic circuit applications, particularly for scalable hybrid
superconductor--semiconductor platforms. However, the robustness of Si:Ga
superconductivity at millikelvin temperatures is yet to be evaluated. Here, we
report the presence of a reentrant resistive transition below T$_{\rm c}$ for
Si:Ga whose strength strongly depends on the distribution of the Ga clusters
that precipitate in the implanted Si after annealing. By monitoring the
reentrant resistance over a wide parameter space of implantation energies and
fluences, we determine conditions that significantly improve the coherent
coupling of Ga clusters, therefore, eliminating the reentrant transition even
at temperatures as low as 20~mK.

Superconductivity;Mesoscale and Nanoscale Physics