Raman imaging of stress in a SiGe/Si photoelastic optical channel waveguide structure

We report Raman imaging of stress in a SiGe/Si optical channel waveguide structure. The difference in thermal expansion coefficients between a Si3N4 stripe and a SiGe layer creates a significant localized stress profile beneath the stripe, which can result in optical confinement suitable for optical waveguide fabrication. We image these areas utilizing Raman polarization selection rules for two transverse optical phonons, relate the Raman peak shifts to strain components, and then to refractive index changes via the photoelastic effect. These micro-Raman images provide spatially resolved two-dimensional refractive index information on the waveguiding region of a channel waveguide structure.