Strain-stabilized highly concentrated pseudomorphicSi1−xCxlayers in Si

We present evidence that ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{C}}_{\mathit{x}}$ layers with x≊0.20 can be grown pseudomorphically on a Si (001) substrate despite the large difference of the C and Si lattice constants. Calculations based on density-functional theory and a Keating model predict that embedded layers of certain structures with stoichiometry ${\mathrm{Si}}_{\mathit{n}\mathrm{-}1}$C where n=5,6,. . . are considerably more stable than isolated C impurities. The common feature of these structures is that the carbon atoms tend to arrange as third-nearest neighbors. Multilayer structures grown by molecular beam epitaxy strongly suggest that defect-free heterostructures with such high C concentrations can be fabricated.