Metamorphic growth of relaxed single crystalline aluminum on silicon (111)

Abstract

Structural characteristics of aluminum thin films have been grown on the 1 × 1, 7 × 7, and √3 × √3 reconstructed Si (111) surfaces by molecular beam epitaxy demonstrating a connection between the nucleation kinetics and grown-in defects of metamorphic epitaxial thin films. High resolution x-ray diffraction symmetric scans and (111) pole figures show that growth on the 1 × 1 reconstructed Si surface produces polycrystalline Al with (100) and (111) diffraction peaks and a large degree of growth twin as determined by a sixfold symmetric pole figure. Growth on the 7 × 7 reconstructed Si surface results in a twinned crystal exhibiting only Al (111) peaks with a sixfold symmetric pole figure. Growth of Al on the √3 × √3 reconstructed surface realizes nearly twin-free single crystal Al (111) film. Atomic force microscopy demonstrates that the Al film roughness improves with crystal quality. Scanning transmission electron microscopy (STEM) shows the twins originate at the substrate/film interface and extend to the film surface indicating that they are growth defects that form during the first few layers of aluminum growth. In addition, STEM indicates that the misfit strain is relaxed within a few monolayers of the interface through a periodic array of misfit dislocations.