Misfit strain and misfit dislocations in lattice mismatched epitaxial layers and other systems

摘要

Heterostructures in the form of thin layers of one material grown on a substrate have been the subject of intense study for several years. In the case of semiconductor systems the aim is to grow epitaxial layers of, for example, Si1-xGex on Si, and devices based on such structures are already in use. Much is known, as is summarized in this review, about the stability of such systems against the insertion of dislocations, and about the critical thicknesses up to which strained layer structures are stable. The effects of dislocation nucleation and the dynamics of dislocation motion which lead to strain relaxation in metastable systems are also reviewed. The present state of theoretical understanding is compared with what is known experimentally. For metallic systems, which often exhibit magnetic properties, the underlying problems of lattice mismatch and strain relief are similar, but much of the interest has been concentrated on the commensurate-incommensurate transition in both structurally and magnetically modulated materials. The theory of this transition is reviewed, both for metallic systems and for epitaxial layers on graphite. In bringing together these different classes of systems within one review, it has been possible to demonstrate the parallels between them. It is hoped that, as a result, transfers of ideas between the fields will be promoted.