Preparation and characterization of Ge epitaxially grown on nano-structured periodic Si pillars and bars on Si(001) substrate

The selective epitaxial growth of germanium on nano-structured periodic silicon pillars and bars with 360 nm periodicity on Si(001) substrate is studied to evaluate the applicability of nano-heteroepitaxy on the Ge-Si system for different fields of application. It is found that SiO₂ used as masking material plays the key role to influence the strain situation in the Si nano-islands. To analyze this in detail, X-ray diffraction techniques in combination with theoretical simulations based on the kinematical X-ray scattering from laterally strained nano-structures and finite element method (FEM) calculations of the strain field are applied. The oxide related strain in the Si scales about linearly with the thickness of the SiO₂ mask, but FEM simulations supposing a homogeneous stress distribution in the oxide are not sufficient to describe the local strain distribution in the nano-structures. It is demonstrated that the Ge lattice relaxes completely during growth on the Si nano-islands by generation of misfit dislocations at the interface, but a high structural quality of Ge can be achieved by suited growth conditions.