Raman scattering spectroscopy has been widely used to characterize the physical properties of semiconductors for at least 20 years. In Raman scattering experiments, monochromatic laser light is focused on the sample and the light scattered inelastically by excitations in the solid is collected and spectrum analyzed. The frequency shifts of the peaks in the Raman spectrum from the laser line position give the energies of the fundamental excitations, which may be electronic or vibrational. More recently, the technique has proved especially valuable for evaluating the mechanical and electronic properties of strained layer superlattices. In particular, for the Si/Sii_xGex system, Raman scattering has been used to evaluate the strain within the alloy and Si layers.