<title>Interfacial chemistry in ZnS/Si and ZnSe/Si superlattices</title>

The potential for hybridization of compound semiconductors with silicon optoelectronics has led to significant efforts in optimizing the heteroepitaxy on Si substrate. Recent experiments show that the epitaxial quality of ZnS/Si (approximately 0.4% mismatch) is not much qualitatively different from that of ZnSe/Si (approximately 4.4% mismatch). This indicates that in semiconductor growth on silicon the formation of interfacial chemical compound plays a more dominant role than the lattice mismatch. In this paper, several ordered structures and disordered pseudobinary alloys are studied in the interface region of ZnS/Si and ZnSe/Si superlattices by using tight-binding calculations. For the ZnSe/Si system, we allow the lattice parameters at interface are relaxed to obtain the energetically most stable structure. The present study gives evidence that ordering induces a preference for lowing density of interface states. In addition, the band offset and layer thickness dependence of the band gap are also calculated.