Novel Chalcogenide Buffer Layer for Oxide Heteroepitaxy on Si(001)

We have developed a novel chalcogenide buffer layer for heteroepitaxial growth of oxides on silicon and applied it to growth of anatase TiO$_2$. Anatase, nearly lattice-matched to Si(001), is of interest for both spintronic and high-K dielectric applications: it can be made ferromagnetic at room temperature by doping with Co, and has a very large dielectric constant. Through use of a sub-nanometer buffer layer, Ga$_2$Se$_3$ grown on As terminated Si(100), we have been able to grow anatase nanocrystals on Si(001) without any detectable substrate oxidation or silicide formation. The As termination prevents silicon-selenide formation, and the gallium selenide prevents substrate oxidation. The cubic structure of Ga$_2$Se$_3$ offers a stable face for TiO$_2$(001) growth. In addition, the Ga$_2$Se$_3$ layer, with a lattice constant between Si and TiO$_2$, has a structure with inherent vacancies that can absorb strain, acting as a strain relief layer for the TiO$_2$ on Si.