Alloys of the form, Si1-xCx, were grown onto Si(001) by means of molecular beam epitaxy under low-pressure C2H4 at 600C. In spite of a relatively high C concentration, as estimated by using X-ray photo-electron spectroscopy and secondary ion mass spectrometry, a good epitaxial relationship with the substrate was revealed by cross-sectional transmission electron diffraction, reconstructed 2 x 1 low-energy electron diffraction and Si 2p X-ray photo-electron diffraction modulated polar patterns for alloys with the cubic symmetry of the Si substrate. On the other hand, the simultaneous absence of relevant X-ray photo-electron diffraction features, significant strain-induced X-ray diffraction shifts and clear C-related local infra-red or Raman modes, suggested that the incorporation of C was different here to the assumed substitutional mode in other Si-C alloys. Inspection by cross-sectional transmission electron microscopy, of samples with the lowest C content, revealed regularly spaced contrast variations which were roughly parallel to the Si/alloy interface; with a periodicity of about 9nm. High-resolution micrographs revealed an almost perfect and unstrained Si lattice, that was free of dislocations or SiC nanocrystal inclusions, between the above strips. With increasing C content, extended defects such as twins or stacking faults appeared in the layer. This produced roughness at the surface, and the striations finally disappeared. The striations could be tentatively accounted for by the pseudomorphic growth of new C-rich phases which matched the C-induced strain, and permitted subsequent strain-free Si growth.

A.Claverie, J.Fauré, J.L.Balladore, L.Simon, A.Mesli, M.Diani, L.Kubler, D.Aubel: Journal of Crystal Growth, 1995, 157[1-4], 420-5