An Investigation into the Role of Energy and Symmetry at Epitaxial Interfaces

Abstract

<p>Epitaxy is a key technological process for the production of thin films and nanostructures for electronic and optoelectronic devices. The epitaxial process has been traditionally studied through the lens of lattice-matched and chemically similar material systems, specifically the III-V quaternary material systems. This work investigates the role energy and symmetry play at epitaxial interfaces for cases far different than those of typical epitaxy. In the realm of energy, the impact of chemically dissimilar epitaxial interfaces was investigated, specifically between semiconductors and oxides, noble metals and oxides, and polar-on-nonpolar epitaxy. For symmetry at epitaxial interfaces, the role of symmetry breaking, through surface reconstructions and asymmetric surfaces was investigated. Investigations into energy found two key insights: 1) epitaxy is possible between materials which one would expect to be very weakly interacting (gold on oxides) and, 2) epitaxial interfaces, while promoting single crystal growth, can be weakly bonded enough to allow controlled liftoff of single crystal epitaxial thin films. Investigations into symmetry at epitaxial interfaces found three key insights: 1) intentional symmetry breaking of the growth substrate through steps can suppress twinning of zincblende thin films, 2) asymmetric (211)-oriented substrates can accommodate strain of mismatched zincblende thin films, and 3) reconstructed oxide substrates can provide unique epitaxial templates for thin films which significantly differ from their bulk lattice. The results of this investigation provide a path towards the improvement of epitaxy through the manipulation of symmetry at epitaxial surfaces, and the production of free standing thin films through the epitaxial liftoff process.</p>