Properties of ZnTe-ZnSe and -ZnS superlattices prepared by hot wall epitaxy

ZnTe-ZnSe and -ZnS superlattices were prepared on GaAs(100) substrates by hot wall epitaxy. Their high-energy electron and θ-2θ X-ray diffraction and photoluminescence at 77 and 300 K were measured. Though the lattice mismatches between the materials are 7% (ZnTe-ZnSe) and 13% (ZnTe-ZnS), strong photoluminescence associated with band edges was observed, i.e. a superlattice consisting of a thin ZnTe layer and a thick ZnSe layer showed strong luminescence associated with band edges and weak luminescence associated with deep level defects. The ZnTe (20 Å)-ZnS (50 Å) superlattice showed strong but rather broad luminescence near 2.6 eV. Variations of the luminescence photon energy of the ZnTe-ZnSe superlattice with the thickness of the ZnTe or the ZnSe layer can be explained qualitatively by strain effects due to the lattice mismatch on the band gap of ZnTe and on the band offsets of the superlattice. The experimental results show the superlattices are of type II, where the conduction and valence band edges of ZnTe are above the corresponding edges of ZnSe or ZnS.