Diffusion of silicon and germanium in Si1−xGex-isotope heterostructures with Ge contents, x = 0, 0.05, 0.25, 0.45 or 0.70, was investigated at 690 to 1270C. The concentration profiles of the stable Si-isotopes and Ge-isotopes were recorded by means of time-of-flight secondary ion mass spectrometry. Analysis of the experimental profiles showed that the Si and Ge diffusion coefficients in elemental Si agreed within experimental accuracy. However with increasing Ge content the diffusion of Ge became increasingly faster compared to that of Si. An Arrhenius-type temperature dependence of diffusion was observed for all compositions, with slightly lower values for the activation enthalpy of Ge compared to Si. The more pronounced Ge diffusion indicated that, with increasing Ge concentration, the diffusional jumps of Ge atoms became more successful compared to those of Si. This trend was explained by an increasing contribution of vacancies to self-diffusion in Si1−xGex with x. In contrast to earlier results the composition dependence of the activation enthalpy of self-diffusion exhibited an upward bowing. A similar composition dependence was reported for the arsenic and antimony diffusion in SiGe and was predicted theoretically for the stability of phosphorus-vacancy and arsenic-vacancy pairs in SiGe. The non-linear behavior seemed to be a general trend and accordingly mainly a consequence of the SiGe alloy system.

Composition Dependence of Si and Ge Diffusion in Relaxed Si1-xGex Alloys. R.Kube, H.Bracht, J.Lundsgaard Hansen, A.Nylandsted Larsen, E.E.Haller, S.Paul, W.Lerch: Journal of Applied Physics, 2010, 107[7], 073520