Investigation of nanostructured germanium/silicon dioxide interfaces

The precipitation of Ge nanoclusters in SiO₂ after implantation arises from their immiscibility and is technologically interesting due to their luminescence and potential use for non-volatile memory devices. Exploiting the same immiscibility, we have recently found that oxidation of germanium-implanted Si surfaces can produce a pileup of Ge in front of the oxidation front and create an atomically sharp interface. In this paper, we examine the band structure and processing of such an interface. Based on ab initio band structure calculations, the band structure of the sharp interface seems to be more favorable for use in electronic devices than the usually diffuse interface in Si/SiO₂. Furthermore, we propose an ab initio based Monte Carlo model to simulate such an oxidation of SiGe alloys. The model explains the formation of the sharp interface due to the repulsive interaction between O and Ge. In such cases, Ge is expelled from the oxide and O atoms do not enter the Ge region under the oxidation front, resulting in strong segregation. Furthermore, inclusion of Ge nanoparticles in the oxide is predicted for higher Ge concentrations, in agreement with experimental results.