Carbon Incorporation During Growth of Epitaxial Germanium(1-Y)carbon(y) Layers on Germanium(001) Substrates

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• D'arcy-Gal, Julie

Contributors dc:contributor

• Greene, Joseph E.

• Physics, Condensed Matter

Language dc:language

eng

Identifier

(MiAaPQ)AAI3017061

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/82697