Group IV semiconductor nanowire arrays: epitaxy in different contexts

Epitaxy can be used to direct nanowire deposition and to influence the crystallographic orientation of nanowires during their nucleation and growth via the vapor-liquid-solid mechanism. We have investigated rapid thermal chemical vapor deposition of epitaxial Ge nanowires and have used it to separately study nanowire nucleation and growth. This work has provided important insights into deep-subeutectic Ge nanowire growth using Au catalyst particles. Germanium nanowires have also been studied as the cores in epitaxial Ge core/Si shell nanowires. We have studied the conditions under which strain-driven surface roughening and dislocations formation occur in these coaxial nanowire heterostructures. Our results indicate that suppression of Si shell surface roughening can lead to fully strained, coherent core/shell nanowires. Recently, we have used vertical arrays of Ge < 111 > nanowires grown at low temperatures on Si substrates to seed liquid-phase epitaxy of large-area amorphous Ge islands above the substrate surface. This work demonstrates a potential approach for dense vertical integration of Ge-based devices on Si substrates, for on-chip optoelectronics or 3D integrated circuit applications.