Abstract
We observe several weak features between 420 and 470 in addition to the normally observed Si-Si (∼500 ), Si-Ge (∼400 ), and Ge-Ge (∼300 ) optic modes in the Raman spectra of (0.28≤x≤0.77) single crystal layers grown by liquid-phase epitaxy (LPE). The quasiequilibrium LPE-growth process rules out the type of long-range ordering recently observed in /Si strained-layer superlattices as the origin for these peaks. Calculations of the first-order Raman spectra of random 216-atom c- alloys reproduce these weak features, which proves that they are not due to second-order Raman processes. Normal-mode analysis shows that they are due to localized Si-Si motion in the neighborhood of one or more Ge atoms. Implications for strain-induced long-range ordering in c- alloys are discussed.
- Received 15 November 1988
DOI:https://doi.org/10.1103/PhysRevB.39.10056
©1989 American Physical Society