Simultaneous diffusion of Si and Ge in isotopically controlled Si1-xGexSi1-xGex heterostructures

Experiments on the diffusion of Si and Ge in Si1-xGexSi1-xGex-isotope heterostructures with Ge contents x=0x=0, 0.05, and 0.25 were performed at temperatures between 870870 and 1270∘C. The concentration profiles of the stable Si- and Ge-isotopes were recorded by means of time-of-flight secondary ion mass spectrometry. For all compositions, an Arrhenius type temperature dependence of diffusion was observed. The activation enthalpy of Si diffusion in SiGe equals the activation enthalpy of Ge diffusion and the pre-exponential factors agree within experimental accuracy. However, the absolute values of the Si and Ge diffusion coefficients indicate a clear trend. In elemental Si the diffusion coefficients of Si and Ge agree, but the difference between the diffusion coefficients of Ge and Si in Si1-xGexSi1-xGex increases with x  . This indicates that with increasing Ge content the diffusional jumps of Ge atoms become more successful compared to that of Si. This trend is explained with an increasing contribution of vacancies to self-diffusion in Si1-xGexSi1-xGex with an increase of the Ge content x.