Low-temperature epitaxial growth of Ge-rich Ge-Si-C alloys: Microstructure, Raman studies, and optical properties

Document Type

Article

Publication Date

8-15-1998

Abstract

Low-temperature (∼200 °C) molecular beam epitaxy of Ge-rich Ge1-x-ySiyCx alloys grown on Si(100) have been investigated by in situ reflection high-energy electron diffraction, ex situ x-ray diffraction, transmission electron microscopy, Raman scattering, and ellipsometry. The Si contents were either ∼20 or ∼40 at % and the C concentrations were nominally varied from zero up to ∼8 at %. Selected samples were annealed in an Ar ambient at 750 °C to evaluate the stability of the thin films. With increasing C concentration, the epitaxial growth mode changes from two-dimensional (2D) layer growth to 3D island growth. Under the growth conditions studied, the GeSiC films have a tendency to form planar defects, whose density increases with increasing C and Si concentrations. The x-ray diffraction data show that the lattice parameter decreases with increasing C concentration. It is estimated that a maximum of ∼2-3 at % C is substitutionally incorporated into these films. Raman spectra of the alloy films show that the effects of C on the strong Ge-Ge and Ge-Si local modes are far less than the effects due to Si. We are unable to observe any systematic change in the Ge-Ge mode, whereas the Ge-Si mode appears to shift to lower frequency with the small addition of C. Ge1-x-ySiyCx films formed by annealing Ge1-XCx films on Si are also discussed. Spectroscopic ellipsometry determinations of the film's optical constants show that the primary effect of C is to reduce the strength of the E1 critical point feature. © 1998 American Institute of Physics.

Publication Title

Journal of Applied Physics

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