Enhanced Electron Mobility in Nonplanar Tensile Strained Si Epitaxially Grown on Si<sub>x</sub>Ge<sub>1-x</sub> Nanowires.
basic_science · Level V
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- Record sourced from PubMed, PMID 29185763.
- Also identified by DOI 10.1021/acs.nanolett.7b03450.
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Abstract
We report the growth and characterization of epitaxial, coherently strained Si<sub>x</sub>Ge<sub>1-x</sub>-Si core-shell nanowire heterostructure through vapor-liquid-solid growth mechanism for the Si<sub>x</sub>Ge<sub>1-x</sub> core, followed by an in situ ultrahigh-vacuum chemical vapor deposition for the Si shell. Raman spectra acquired from individual nanowire reveal the Si-Si, Si-Ge, and Ge-Ge modes of the Si<sub>x</sub>Ge<sub>1-x</sub> core and the Si-Si mode of the shell. Because of the compressive (tensile) strain induced by lattice mismatch, the core (shell) Raman modes are blue (red) shifted compared to those of unstrained bare Si<sub>x</sub>Ge<sub>1-x</sub> (Si) nanowires, in good agreement with values calculated using continuum elasticity model coupled with lattice dynamic theory. A large tensile strain of up to 2.3% is achieved in the Si shell, which is expected to provide quantum confinement for electrons due to a positive core-to-shell conduction band offset. We demonstrate n-type metal-oxide-semiconductor field-effect transistors using Si<sub>x</sub>Ge<sub>1-x</sub>-Si core-shell nanowires as channel and observe a 40% enhancement of the average electron mobility compared to control devices using Si nanowires due to an increased electron mobility in the tensile-strained Si shell.