Strain in a single ultrathin silicon layer on top of SiGe islands: Raman spectroscopy and simulations

By means of resonant Raman spectroscopy we investigated the strain on a single ultrathin crystalline silicon layer, locally induced by buried SiGe nanostructures. The spectrum of a 5-nm-thick silicon layer on top of SiGe islands shows a single highly strained feature attributed to the out-of-plane phonon. The direct comparison of the experimental results with finite-element methods through spectral simulation shows excellent agreement that clarifies the physical origin of the spectrum. An increase in the silicon layer thickness up to 40 nm results in a progressive reduction in the strain