Epitaxial metastable Ge1–yCy alloy layers, where y was below 0.035, were grown onto Ge(001) from hyperthermal Ge and C atomic beams at deposition temperatures of 250 and 300C. The use of hyperthermal beams permitted controllable variations in the

concentration of C which was incorporated as Ge-C split interstitials. The Ge1–yCy layers which were grown using incident Ge-atom energy distributions that corresponded to less than 0.14dpa were in a state of in-plane tension and contained significant concentrations of C atoms which were incorporated at substitutional sites. An increase to 0.24dpa yielded layers that were in compression; with the C incorporated mainly as Ge-C split interstitials. First-principles density functional calculations of the formation energies and strain coefficients that were associated with C atomic arrangements in Ge showed that configurations which contained multiple C atoms (known collectively as C nanoclusters) were energetically more favorable than substitutional C and Ge-C split interstitials and yielded an almost zero average strain. On the other hand, substitutional C and Ge-C split interstitials produced large tensile and compressive strains, respectively. By using the calculated strain coefficients, measured layer strains obtained from high-resolution reciprocal lattice maps, and substitutional C concentrations determined by Raman spectroscopy, the fraction of C atoms which was incorporated at substitutional, Ge-C split interstitial and nanocluster sites was obtained as a function of the total C concentration and the deposition temperature. It was found that, at low C concentrations and deposition temperatures, all of the C atoms were incorporated at single-C configurations, such as substitutional C and Ge–C split interstitials. Their relative concentrations were controlled by the dpa-value, via the production of near-surface Ge self-interstitials which were trapped by substitutional C atoms to form Ge-C split interstitials. Increasing the C concentration and deposition temperature, regardless of the dpa-value, led to an increase in the fraction of C nanoclusters, while the fractions of substitutional C and Ge–C split interstitials decreased due to the higher C-C encounter probability at the growth surface.

Quantitative C Lattice Site Distributions in Epitaxial Ge1–yCy/Ge(001) Layers. J.D’Arcy-Gall, D.Gall, I.Petrov, P.Desjardins, J.E.Greene: Journal of Applied Physics, 2001, 90[8], 3910-8