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| Home>Research>MC2-Crystalline Materials under Stress>Stress and nanostructuration>Epitaxial layers | ||||||||||||||
Development of new methods for measuring local strains and stresses in epitaxial layers |
| Marie-José Casanove, François Demangeot, Lise Durand, Christophe Gatel, Anne Ponchet, Christian Roucau |
| We are developing new methods to analyse stress and strain in epitaxial heterostructures where the active zones are nanometric (thin layers, quantum wells, quantum boxes....). Our approaches are based on: - Raman micro-spectroscopy in order to establish strain mapping - Transmission electron microscopy
(TEM) with 3 main axis in development :
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- Finite element modeling (FEM), which are systematically coupled to TEM in order to account for the surface relaxation effect (i.e. the modification of the stress state by the sample thinning). These approaches are mainly applied to III-V (GaN, GaAs, GaInAs, InP…) and Si/SiGe semiconductors nanostructures which constitute active zones in opto and micro-electronic devices. Lattice mismatches are typically of a few percent, which corresponds to in-plane component of stress of the order of magnitude of a few GPa. Oxide and metallic systems for magnetic applications are also studied. |
TEM curvature method for epitaxial stress measurement |
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| Bending, which is due to specimen thinning, can be exploited to measure epitaxial stresses. The radius of curvature is measured by bend contours in plan-view configuration (dark lines on the TEM image below) and is modeled by finite elements. In this sample (10 nm of GaInAs on GaAs), we have thus measured an epitaxial stress of -1.6 GPa. On the right, cylindrical curvature, below, spherical curvature. Appl. Phys. Lett. 86, 191901 (2005). |
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Epitaxial strain from Convergent Beam Electron Diffraction patterns (CBED) |
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| Exemple of a Si0.8Ge0.2 layer (27 nm) on Si. The CBED pattern shown here has been performed at a depth of 200 nm from the surface (the sample being thinned in cross-section). The broadening of the CBED lines is due to the crystalline plane bending (thin foil relaxation). |
We have developed a new approach (TDDT - Time Dependent Dynamical Theory) which allows the simulation of such patterns from finite element modeling. Ultramicroscopy 108, 426-432 (2008). |
 
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Strain mapping
by Raman micro-spectroscopy |
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In plane (εxx) and out of plane (εzz) strains measured in a 300 nm thick AlN layer grown by MOVPE on a 2 μm thick GaN buffer (saphir substrate). Optical phonons scattering (visible micro-Raman) are used as internal probes to analyse the strain ; a spatial cartography is allowed by the micro-Raman technique. Here it is shown the variation of the strain in AlN as function of the distance to some cracks present in this layer. J. Crystal Growth 299, 254 (2007).
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Publications M. Cabié, Thèse de Doctorat de l'Université Paul Sabatier de Toulouse (2005) F. Houdellier, Thèse de Doctorat de l'Université Paul Sabatier de Toulouse (2006) New approach for the dynamical simulation of CBED patterns in heavily strained specimens, Houdellier F, Altibelli A, Roucau C and Casanove MJ, Ultramicroscopy 108, 426-432 (2008) Effect of sample bending on diffracted intensities observed in CBED patterns of plan view strained samples, F. Houdellier, D. Jacob, MJ. Casanove and C. Roucau, Ultramicroscopy 108, 295-301 (2008) Strain relaxation of thick AlN layers for Stranski-Krastanov quantum dots formation in vapour phase epitaxy, D. Simeonov, E. Feltin, F. Demangeot, C. Pinquier, R. Butté, J.-F. Carlin, J. Frandon, N. Grandjean, J. Crystal Growth 299, 254 (2007) Convergent beam electron diffraction for strain determination at the nanoscale, Houdellier F, Roucau C and Casanove MJ, Microelectronic Engineering 84, 464-467 (2007) Quantitative analysis of HOLZ line splitting in CBED patterns of epitaxially strained layers, Houdellier F, Roucau C, Clement L, Rouvière JL and Casanove MJ, Ultramicroscopy 106, 951-959 (2006) Raman scattering study of wurtzite and rocksalt InN under high pressure, Pinquier C, Demangeot F, Frandon J, Chervin JC, Polian A, Couzinet B, Munsch P, Briot O, Ruffenach S, Gil B, Maleyre B, Phys. Rev. B 73, 115211 (2006) Electronic conductivity and structural distortion at the interface between insulators SrTiO3 and LaAlO3, J.-L. Maurice, C. Carretero, M.-J. Casanove, K. Bouzehouane, S. Guyard, É. Larquet, and J.-P. Contour, Phys. Stat. Sol. a 203, 2209-2214 (2006) Geometrical criteria required for the determination of the epitaxial stress from the transmission electron microscopy curvature method, M. Cabié, A. Ponchet, A. Rocher, L. Durand, and A. Altibelli, Appl. Phys. Lett. 86, 191901 (2005) Transmission Electron Microscopy and Raman measurements of the misfit stress in a Si tensile strained layer, M. Cabié, A. Ponchet, A. Rocher, V. Paillard and L. Vincent, Appl. Phys. Lett. 84, 870-872 (2004) TEM measurement of the misfit stress by a curvature method in semiconducting epitaxial system, A. Ponchet, M. Cabié and A. Rocher, Eur. Phys. J. Appl. Phys. 26, 87-94 (2004) Phonon deformation potentials in hexagonal GaN,, F. Demangeot, J. Frandon, P. Baules, F. Natali, F. Semond et J. Massies, Phys. Rev. B 69, 155215 (2004) Raman scattering in hexagonal InN under high pressure, Pinquier
C, Demangeot F, Frandon J, Pomeroy JW, Kuball M, Hubel H, van Uden
NWA, Dunstan DJ, Briot O, Maleyre B, Ruffenach S, Gil B, Phys. Rev.
B 70, 113202 (2004) |
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Key-words: stress, strain, epitaxy, elasticity, surface relaxation, thin foil, curvature, bending , CBED, HREM, TEM, finite element, optical micro-spectroscopy, Raman
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