Quantitative C lattice site distributions in epitaxial Ge{sub 1-y}C{sub y}/Ge(001) layers
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)
- DOE Contract Number:
- FG02-96ER45439
- OSTI ID:
- 40277863
- Journal Information:
- Journal of Applied Physics, Vol. 90, Issue 8; Other Information: DOI: 10.1063/1.1402137; Othernumber: JAPIAU000090000008003910000001; 015120JAP; PBD: 15 Oct 2001; ISSN 0021-8979
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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