Quantitative C lattice site distributions in epitaxial Ge{sub 1-y}C{sub y}/Ge(001) layers

Journal Article · Mon Oct 15 04:00:00 EDT 2001 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1402137· OSTI ID:40277863

D'Arcy-Gall, J; Gall, D; Petrov, I; Desjardins, P; Greene, J E

Epitaxial metastable Ge{sub 1-y}C{sub y} alloy layers with y{<=}0.035 were grown on Ge(001) from hyperthermal Ge and C atomic beams at deposition temperatures T{sub s} of 250 and 300 C. The use of hyperthermal beams allows us to controllably vary the concentration of C incorporated as Ge--C split interstitials. Ge{sub 1-y}C{sub y} layers grown with incident Ge-atom energy distributions corresponding to {<=}0.14 lattice displacement per incident atom (dpa) are in a state of in-plane tension and contain significant concentrations of C atoms incorporated in substitutional sites. Increasing the dpa to 0.24 yields layers in compression with C incorporated primarily as Ge--C split interstitials. Ab initio density functional calculations of the formation energies and strain coefficients associated with C atomic arrangements in Ge show that configurations containing multiple C atoms, referred to collectively as C nanoclusters, are energetically more favorable than substitutional C and Ge--C split interstitials and yield a nearly zero average strain. In contrast, substitutional C and Ge--C split interstitials produce large tensile and compressive strains, respectively. Using the calculated strain coefficients, measured layer strains obtained from high-resolution reciprocal lattice maps, and substitutional C concentrations determined by Raman spectroscopy, we obtain the fraction of C atoms incorporated in substitutional, Ge--C split interstitial, and nanocluster sites as a function of the total C concentration y and T{sub s}. We find that at low y and T{sub s} values, all C atoms are incorporated in single-C configurations: substitutional C and Ge--C split interstitials. Their relative concentrations are controlled by the dpa through the production of near-surface Ge self-interstitials which are trapped by substitutional C atoms to form Ge--C split interstitials. Increasing y and T{sub s}, irrespective of the dpa, leads to an increase in the fraction of C nanoclusters, while the fractions of substitutional C and Ge--C split interstitials decrease, due to the higher C--C encounter probability at the growth surface.

• Sponsoring Organization: (US)
• OSTI ID: 40277863
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 8 Vol. 90; ISSN 0021-8979
• Publisher: The American Physical Society
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALLOYS
ATOMIC BEAMS
ATOMS
COMPRESSION
DEPOSITION
ENERGY SPECTRA
FUNCTIONALS
INTERSTITIALS
PROBABILITY
PRODUCTION
RAMAN SPECTROSCOPY
STRAINS