A STUDY OF OXYGEN-IMPLANTED SI0.5GE0.5 ALLOY BY XPS AND THERMODYNAMIC ANALYSIS

A thermodynamic study of oxygen-implanted Si0.5Ge0.5 alloy based on an XPS analysis is reported for the first time. The alloy was grown by molecular beam epitaxy (MBE) and was implanted with high-dose oxygen ions (up to 1.8 x 10(18) cm-2) at an energy of 200 keV. The changes of Si, Ge and O activities with the concentration of oxygen were calculated using the THERMO-CALC program, and chemical potentials of these elements throughout the oxygen-buried region were plotted out according to the chemical state information obtained from XPS depth profiling results. Transport during implantation and in subsequent annealing follows the gradient of chemical potential: elemental Si migrates into the oxygen-rich layer to form SiO2 by the replacement of Ge in Ge oxides. This leads to a decrease of the total free energy for the system of Si, Ge and O in the sample. The description of the system in terms of activities and chemical potential enables true diffusion profiles to be used in place of phenomenological descriptions such as 'snowplough' or 'pile-up'.