Composition dependence of Si and Ge diffusion in relaxed Si1−xGex alloys

Abstract

Diffusion of silicon (Si) and germanium (Ge) in silicon-germanium Si1−xGex-isotope heterostructures with Ge contents x=0, 0.05, 0.25, 0.45, and 0.70 was investigated in a temperature range between 690 and 1270 °C. 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 shows that the Si and Ge diffusion coefficients in elemental Si agree within experimental accuracy. However with increasing Ge content the diffusion of Ge gets increasingly faster compared to that of Si. An Arrhenius type temperature dependence of diffusion is observed for all compositions with slightly lower values for the activation enthalpy of Ge compared to Si. The more pronounced Ge diffusion indicates that with increasing Ge concentration the diffusional jumps of Ge atoms become more successful compared to those of Si. This trend is explained with 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 reveals an upward bowing. A similar composition dependence is reported for the arsenic (As) and antimony (Sb) diffusion in SiGe and is predicted theoretically for the stability of phosphorus-vacancy and arsenic-vacancy pairs in SiGe. The nonlinear behavior seems to be a general trend and accordingly mainly a consequence of the SiGe alloy system.

Bowing of the defect formation energy in semiconductor alloys

“…Since the electronic occupation and size of defects depend on charge states, the bowing of the defect formation energy should also be charge-dependent. Our theoretical model is consistent with experimental observations [24][25][26]. For examples, it is observed that Cu atoms accumulate in the mixed CdS x Te 1−x alloy region when small amount of S is mixed into CdTe at the CdTe/CdS interfaces in CdTe based solar cell [25].…”

Germanium-silicon alloy and core–shell nanocrystals by gas phase synthesis

“…The Ge diffusion is very slow under strain free conditions 40,41 and seems to be enhanced by the growth mechanism as discussed in the following. The deposition of Si on Ge is governed by the 4.2% lattice mismatch between the two materials.…”

Vacancy-oxygen defects in p-type Si1−xGex

“…9,10 Interestingly, in previous experimental and theoretical studies it was shown than the structure and defect processes do not exhibit a Vegard law type behavior. 11,12 That is they cannot be determined by a simple linear interpolation of the respective properties of Si and Ge, which are the end members of Si 1-x Ge x . The deviations are typically larger for intermediate Ge contents, however, they can appear to be non-existent for very small or very large Ge contents.…”