  We have fabricated a superconductor/semiconductor junction composed of Al and
InAs using cleaved edge overgrowth (CEO). By exploiting the unique geometry
with a thin Al/Pt/Al trilayer formed on the side surface of an in-situ cleaved
heterostructure wafer containing an InAs quantum well (QW), we achieve a
superconducting critical field of $\sim 5$~T, allowing superconductivity and
quantum Hall (QH) effects to coexist down to filling factor $\nu = 3$. Andreev
reflection at zero magnetic field shows a conductance enhancement that is
limited solely by the Fermi velocity mismatch, demonstrating a virtually
barrier-free, high-quality S/Sm junction. Bias spectroscopy in the QH regime
reveals a clear bias dependence indicating the superconducting gap, with the
reduced downstream resistance demonstrating that the electron-hole Andreev
conversion probability consistently exceeds 50\%. Our results, obtained in a
new experimental regime characterized by a clean edge-contacted junction, a
much smaller superconducting gap, and a narrow superconducting electrode less
than the coherence length, open a new avenue for both theoretical and
experimental studies of the interplay between superconductivity and QH effects
and the engineering of exotic quasiparticles.
