Carbon self-organization in the ternary Si1−x−yGexCy alloy

Abstract

This article demonstrates for the first time the possible self-ordering of carbon in Si1−x−yGexCy thin films pseudomorphically grown on silicon. Germanium and carbon atomic distributions have been studied for a C-rich Si0.9−yGe0.1Cy heterostructure using high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction, Raman spectrometry, and secondary ion mass spectrometry (SIMS). HRTEM images show the spontaneous formation of carbon-rich tilted sublattices and local germanium fluctuations, despite constant growth parameters. X-ray diffraction confirms this thin sublayers formation. A complementary insight into local ordering effects around C is obtained by Raman spectroscopy. A new model for perpendicular lattice parameter reduction is proposed. It involves C atoms mostly in third-nearest-neighbor positions and the local formation of a distorted CSi3 graphitic arrangement. In these C-rich sublayers, the perpendicular lattice mismatch to silicon is as low as −0.014. This aperiodic structure remains highly distorted and a statistical description of these strain fluctuations is detailed. The atomistic configuration of these δ layers indicates the likely contribution of surface steps during the growth, while SIMS measurements hint at the probable involvement of carbon interstitials to explain this ordering. For technological applications, this self-organization of carbon is promising for the ultrashallow junction challenge. These carbon-rich embedded layers can be considered as quantum wells, etch stops or very thin barriers against transient enhanced diffusion.