Amorphous superlattices of chalcogenides

Abstract

After the first work on superlattices by Esaki and Tsu [1] in 1970 the investigations on low-dimensionality hetero- and homostructures increase progressively. The molecular beam epitaxy opened possibilities for the growth of semiconductor atomic layer upon atomic layer. This and other techniques have been used to grow ultrathin, well-controlled systems. The various structures may be classified by means of their band diagrams. Single and multiple quantum wells, single and double barrier tunneling structures, incoherent multilayer tunneling structures and superlattices, are the main ones [21. It can be mentioned that in the structures defined as multiple quantum wells the barrier thickness may be large enough to prevent tunneling. In the superlattice structure disorder and scattering must be low enough to allow the coherent superlattice band states to be built up and to prevent destruction of the phase coherence between the tunneling states by disordered interface fluctuations. Nevertheless, usually all the mentioned multilayers are refered as superlattices. Since the mid-Seventies, bandgap engineered multilayer structures with desired properties and new devices based on them have been prepared from III-V materials.