Epitaxial Growth of High Quality Ge Films on Si(001) Substrates by Nanocontact Epitaxy

We have developed a novel epitaxial growth technique called nanocontact epitaxy that allows high quality Ge films to be epitaxially grown on Si(001) substrates using spherical nanodots as seed crystals. The nanodots only make contact with the Si substrate through nanowindows in an intermediate ultrathin SiO 2 film, and they were elastically strain-relaxed without misfit dislocations. Ge films with a thickness of 130 nm were epitaxially grown on the nanodot seed crystals by solid source molecular beam epitaxy. The resulting Ge films typically exhibited a surface roughness of ∼0.4 nm and an etch pit density of 10 4 to 10 5 cm –2, demonstrating their high crystallinity. The films exhibit photoluminescence around 0.8 eV related to Ge crystals.