Carbon Incorporation During Growth of Epitaxial Germanium(1-Y)carbon(y) Layers on Germanium(001) Substrates
D'arcy-Gal, Julie
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https://hdl.handle.net/2142/82697
Description
Title
Carbon Incorporation During Growth of Epitaxial Germanium(1-Y)carbon(y) Layers on Germanium(001) Substrates
Author(s)
D'arcy-Gal, Julie
Issue Date
2001
Doctoral Committee Chair(s)
Greene, Joseph E.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
Epitaxial metastable Ge1-yCy alloy layers with y ≤ 0.035 were grown on Ge(001) from hyperthermal Ge and C atomic beams at deposition temperatures 250 ≤ Ts ≤ 550°C. I show that the use of hyperthermal beams allows me to controllably vary the concentration of C incorporated as Ge-C split interstitials. Ge1-y Cy layers grown with incident Ge-atom energy distributions corresponding to ≤0.14 lattice d&barbelow;isplacement p&barbelow;er incident a&barbelow;tom (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, I calculate 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 Ts. I find that at low y and Ts 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 Ts, 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.
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