6 - Semiconductor Atomic Superlattice (SAS)

Abstract

This chapter gives a good example of how an idea was developed and metamorphosed into an all epitaxially formed structure. The process is fundamentally different from ALE, because in semiconductor atomic superlattice (SAS), for Si–O superlattice, silicon dictates what sites oxygen can occupy consistent with the surface reconstruction, whereas in ALE, no one constituent dictates, resulting in a random alloy. Superlattices and quantum wells were introduced as man-made quantum structures to engineer the quantum states for electrical and optical applications. The idea relies heavily on the availability of good heterojunctions, lattice-matched systems, and later, strain-layer systems. A new type of superlattice was proposed, the epilayer doping superlattice (EDS), consisting of, for example, a couple of layers of Si in AlP. The idea is fundamentally different from atomic plane- or δ-doped doped superlattices, where only a small fraction of the plane is occupied by doping or substitution. Basically, if the entire layer is involved, unlike doping, disorder is eliminated. Another type of superlattice designed to incorporate extremely localized interactions that is most promising for silicon was introduced by Tsu (1993), consisting of an effective barrier to silicon, formed by a suboxide with a couple of monolayers of oxygen atoms. To overcome the problem of structural robustness associated with porous silicon, p-Si, it was proposed that nanoparticles of silicon with a size in the range of several nanometers sandwiched between thin oxide layers to form a superlattice may solve the problem of mechanical robustness while retaining the features of quantum confinement as in the case of porous silicon, where the name “interface adsorbed gas-superlattice” (IAG-superlattice) was introduced.