  Radiative cascades emit correlated photon pairs, providing a pathway for the
generation of entangled photons. The realization of a radiative cascade with
impurity atoms in semiconductors, a leading platform for the generation of
quantum light, would therefore provide a new avenue for the development of
entangled photon pair sources. Here we demonstrate a radiative cascade from the
decay of a biexciton at an impurity-atom complex in a ZnSe quantum well. The
emitted photons show clear temporal correlations revealing the time--ordering
of the cascade. Our result establishes impurity atoms in ZnSe as a potential
platform for photonic quantum technologies using radiative cascades.
