Univ. Grenoble Alpes, CEA-INAC, 17 rue des Martyrs, Grenoble, France, Univ. Grenoble Alpes, CEA-LETI, Minatec Campus, 17 rue des Martyrs, Grenoble, France, Laboratory for Micro- and Nanotechnology, Paul Scherrer Institute, Villigen, Switzerland, Institute for Quantum Electronics, ETH Zurich, Zürich, Switzerland

The application of high values of strain to Ge considerably improves its light emission properties and can even turn it into a direct band gap semiconductor. Raman spectroscopy is routinely used for strain measurements. Typical Raman-strain relationships that are used for Ge were defined up to ?1% strain using phonon deformation potential theory. In this work, we have studied this relationship at higher strain levels by calculating and measuring the Raman spectral shift-strain relations in several different strain configurations. Since differences were shown between the usual phonon deformation potential theory and ab-initio calculations, we highlight the need for experimental calibrations. We have then measured the strain in highly strained Ge micro-bridges and micro-crosses using Raman spectroscopy performed in tandem with synchrotron based micro-diffraction. High values of strain are reported, which enable the calibration of the Raman-strain relations up to 1.8% of in plane strain for the (001) biaxial stress, 4.8% strain along ?100?, and 3.8% strain along ?110?. For Ge micro-bridges, oriented along ?100?, the nonlinearity of the Raman shift-strain relation is confirmed. For the ?110? orientation, we have shown that an unexpected non-linearity in the Raman-strain relationship has also to be taken into account for high stress induction. This work demonstrates an unprecedented level of strain measurement for the ?110? uniaxial stress and gives a better understanding of the Raman-strain relations in Ge. © 2017 Author(s).

Calculations, Calibration, Deformation, Energy gap, Germanium, Mechanics, Phonons, Raman spectroscopy, Strain measurement, Ab initio calculations, Deformation potential theory, Direct band gap semiconductors, Experimental calibration, Highly strained, In-plane strains, Light emission properties, Uniaxial stress, Strain