  Using Andreev reflection (AR) as an experimental gauge of the superconducting
proximity effect (PE), we assess the topological purity of the
superconductivity that is induced by the c-axis PE between an s-wave
superconductor and the topological insulators Bi$_{2}$X$_{3}$ (X=Se,Te).
Point-contact AR spectroscopy is performed with Nb tips on Bi$_{2}$X$_{3}$
single crystals at 4.2 K. Scanning tunneling spectroscopy is also used, to
locate the Fermi level $E_F$ relative to the Dirac point in the crystals. The
AR data is analyzed with Blonder-Tinkham-Klapwijk theory, taking into account
tip-induced spin-orbit coupling, Fermi-surface mismatch, and the co-presence of
bulk band and topological surface states at $E_F$. Our results indicate that
the superconductivity that can be proximity-induced into Bi$_{2}$X$_{3}$ is
predominantly non-topological.
