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 st ructure. The difference in thermal expansion coefficients between a Si3N4 s tripe and a SiGe layer creates a significant localized stress profile benea th the stripe, which can result in optical confinement suitable for optical waveguide fabrication. We image these areas utilizing Raman polarization s election rules for two transverse optical phonons, relate the Raman peak sh ifts to strain components, and then to refractive index changes via the pho toelastic effect. These micro-Raman images provide spatially resolved two-d imensional refractive index information on the waveguiding region of a chan nel waveguide structure. (C) 1999 American Institute of Physics. [S0003-695 1(99)04135-2].