Raman spectroscopy is used to study vibrational, rotational and other low energy states. The inelastically scattered photon of a monochromatic beam has lost or gained energy of the scattering partner. The energy shift, the intensity, the spectrum and the polarization of the scattered light give access to properties of the material under investigation. The signatures in the Raman spectra carry information on crystallinity, orientation, composition, stress, temperature, doping and relaxation and other properties. Therefore the interpretation of the spectra can be rather complex.