Test of Vegard's law in thin epitaxial SiGe layers

“…A good illustration of the experimental difficulties associated with thin film measurements is provided by the work of Kasper et al, 14 who determined the lattice parameter in Si 1-x Ge x films grown pseudomorphically on Si and could only verify Dismukes' earlier bulk data 4 in a semi-quantitative way due to the uncertainties in the Ge concentrations and in the strain corrections. In the case of Ge 1-y Sn y alloys, the experimental evidence so far is based on measurements of Ge 1-y Sn y films grown directly on (001) Si.…”

mentioning

confidence: 99%

Nonlinear structure-composition relationships in the Ge1−ySny/Si(100) (y<<

et al. 2011

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The compositional dependence of the cubic lattice parameter in Ge 1-y Sn y alloys has been revisited. Large 1000-atom supercell ab initio simulations confirm earlier theoretical predictions that indicate a positive quadratic deviation from Vegards' law, albeit with a somewhat smaller bowing coefficient, θ = 0.047 Å, than found from 64-atom cell simulations (θ = 0.063 Å). On the other hand, measurements from an extensive set of alloy samples with compositions y < 0.15 reveal a negative deviation from Vegard's law. The discrepancy with earlier experimental data, which supported the theoretical results, is traced back to an unexpected compositional dependence of the residual strain after growth on Si substrates. The experimental bowing parameter for the relaxed lattice constant of the alloys is found to be θ = -0.066 Å. Possible reasons for the disagreement between theory and experiment are discussed in detail.

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“…A more exact calculation considering parabolic deviation of lattice constant of SiGe [17,18] delivers slight negative values of R Si . This underlines that Raman measurements of R Si are only accurate within about 10% limits.…”

Section: Raman Characterization Of Local S-simentioning

confidence: 98%