Raman and RAS Measurements on Uniaxially Strained Thin Semiconductor Layers

A sensitive and reliable method was developed for the determination of electron and phonon deformation potentials of thin layers and layered structures. A device was constructed and used to apply a line force at the center of a narrow stripe cut from a semiconductor wafer. The induced strain along the stripe was calculated from the maximum deflection at the center of the stripe. Thin layers of Si, SiGe and InGaAs were studied and the information on the phonon deformation potentials was deduced from the phonon frequency shift measured by Raman spectroscopy. Strain dependent changes in electronic band structure were monitored by means of Reflectance Anisotropy Spectroscopy (RAS). The RAS spectra consisted of sharp peaks at or near bandgap energies which increased rapidly with even a small increase of strain. The uniaxial strain device used with RAS is shown to provide a very sensitive technique for the detection of small amounts of strain. This method could be also applied for the study of superlattices.