Anomalous Ge diffusion effects during Ge-condensation

Thin Si_0.88 Ge_0.12 layers were grown by LP- CVD on thick (100 nm) silicon-on-insulator for Ge condensation studies. A series of oxidations was carried out to reveal aspects of the Ge condensation process and the final structures were characterised by SIMS and X-TEM. The SIMS data showed that during the early stages, Ge diffuses through the buried oxide (BOX) and accumulates in the underlying Si-substrate. Intriguingly, as the condensation process continues this Ge appears to be re-incorporated into condensed layer above the BOX. We suggest a possible mechanism to account for this phenomenon.