We examine in detail the photoluminescence properties of the DX center in periodically &dgr;‐doped Si‐AlxGa1−xAs (x=0.32). The DX center is shown to be band structure dependent rather than a conduction miniband resonance. New photoluminescence lines at energies below the band gap at 1.878, 1.787, and 1.695 eV have been detected, and ascribed to a radiative recombination of electrons in confined subbands or in minibands with holes located at the top of the valence band between the &dgr; layers.