Epitaxial metastable Ge1–yCy alloy layers, where y was below 0.045, were grown onto Ge(001) by means of solid-source molecular-beam epitaxy at 200 to 400C. By using calculated strain coefficients and measured layer strains, obtained from high-resolution reciprocal lattice maps, the C lattice-site distributions were determined as a function of the deposition temperature and total C concentration. High-resolution reciprocal lattice maps showed that all of the as-deposited alloys were completely coherent with their substrates. The Ge1–yCy(001) layers which were grown at deposition temperature of up to 350C were in a state of in-plane tension and contained C at substitutional sites (giving rise to tensile strains) and at nanocluster sites; which introduced a negligible lattice strain. Layers which were deposited at 400C were strain-neutral, with negligible substitutional C contents. Increasing the y-value and/or the deposition temperature led to a decrease in substitutional C concentration (consistent with Raman spectroscopy results), with a corresponding increase in the C fraction incorporated at nanocluster sites. The latter suggested that nanocluster formation was kinetically limited, during film deposition, by the C-C adatom encounter probability at the growth surface. The overall results showed that it was not possible, using molecular beam epitaxy, to obtain fully substitutional C incorporation in Ge1–yCy(001); regardless of the y-value and deposition temperature. This was consistent with ab initio density functional calculations which showed that C incorporation at nanocluster sites was energetically favored over incorporation at

substitutional Ge lattice sites. Annealing the Ge1–yCy(001) layers at 550C led to a significant decrease in the substitutional C fraction, and therefore a lower tensile strain. Layers which were annealed at 650C were strain-free, because all of the substitutional C had migrated to lower-energy nanocluster sites.

C Lattice Site Distributions in Metastable Ge1–yCy Alloys Grown on Ge(001) by Molecular-Beam Epitaxy. S.Y.Park, J.D’Arcy-Gall, D.Gall, Y.W.Kim, P.Desjardins, J.E.Greene: Journal of Applied Physics, 2002, 91[6], 3644-52