Thermodynamic behaviour of GeO2 formed by oxygen implantation into relaxed Si0.5Ge0.5 alloy

The thermal stability of GeO2 formed by oxygen implantation into Si0.5Ge0.5 alloy has been investigated and quantified. The sample used in this experiment consisted of a 900 nm relaxed layer of Si0.5Ge0.5 alloy capped with 78 nm of silicon which was grown on a (100) Si n-type wafer. This was then implanted with a dose of 1.8 × 1018 O+/cm2 at 200 keV and specimens from the implanted region were annealed for 1 h at various temperatures. The composition and thickness of the oxide layer, which consisted of SiO2 + GeO2, and redistribution of elemental silicon, germanium and oxygen were determined by Rutherford backscattering spectroscopy. The chemical bonding of silicon and germanium to oxygen was determined using X-ray photoelectron spectroscopy. It is found that the germanium was rejected from the oxide layer and segregated at the interface between SiGe/oxide and oxide/SiGe. The driving force for the mass transport can be attributed to the higher chemical potential of germanium in the oxide layer, which is a consequence of the difference in the free energies of formation of SiO2 and GeO2.