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Measurement of phonon pressure coefficients for a precise determination of deformation potentials in SiGe alloys
Author(s) -
Reparaz J. S.,
Goñi A. R.,
Bernardi A.,
Alonso M. I.,
Garriga M.
Publication year - 2009
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200880531
Subject(s) - phonon , materials science , hydrostatic pressure , condensed matter physics , raman scattering , raman spectroscopy , silicon , deformation (meteorology) , alloy , molecular beam epitaxy , substrate (aquarium) , stress (linguistics) , elastic modulus , optics , epitaxy , layer (electronics) , optoelectronics , composite material , thermodynamics , physics , linguistics , oceanography , philosophy , geology
For an effective use of Raman scattering as strain characterization tool in SiGe nanostructures a precise knowledge of the phonon deformation potentials (DPs) is strictly necessary. The optical phonon DPs can be determined by means of Raman scattering measurements from the cleaved edge of a biaxially strained SiGe alloy layer grown pseudomorphically on silicon and subsequently capped. Due to uncertainties in the literature values of the unstrained phonon frequencies it turns out that the desired degree of accuracy is only attained by complementing the Raman measurements from the edge with that of the hydrostatic pressure coefficient of the optical phonons. For that purpose we have grown by molecular beam epitaxy up to seven partially strained Si 1– x Ge x alloys on Si spanning the entire compositional range and measured the dependence on hydrostatic pressure of the frequency of the Ge‐like, Si‐like and mixed Si–Ge optical modes. After correcting for the pressure dependent biaxial stress induced by the Si substrate on the alloy layer and taking into account the dependence on alloy composition of the bulk modulus we obtain a fairly constant value of the Grüneisen parameter around 1.0 for all three optical modes in the whole range of Ge contents. We also determined the strain shift coefficients for the three modes, which are essentially independent of Ge content between 0.4 and 1. Our results are in very good agreement with recentcalculations of the SiGe phonon deformation potentials using a modified Keating model, which settles the longstanding issue about the large discrepancies between results from different experiments. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)