Mapping of local stress distributions in SiGe/Si optical channel waveguide

Micro-Raman scattering experiments have been carried out to study a SiGe/Si photoelastic optical channel waveguide structure. A Si3N4 stressor stripe was fabricated on a SiGe/Si planar waveguide to create local stress variati on beneath the stripe. To characterize the local stress distributions which create the channel waveguide structure, we obtained Si-Si Raman peak shift s in the SiGe layer by utilizing spatially resolved Raman spectra both from the top surface across the width of the Si3N4 stripe and from an edge (i.e ., a waveguiding region) beneath the stripe. Longitudinal optical phonon sh ifts observed from the top surface show a significant increase in compressi ve stress within the stripe width and in tensile stress just outside of str ipe edges for a sample annealed at 600 degreesC. To map local changes of st resses in the waveguiding region beneath the stripe, spectra from two trans verse optical phonons were measured from the edge and interpreted using the Raman polarization selection rules. The Si-Si Raman peak shifts obtained w ere used to find strain components and, in turn, to model resultant local r efractive index variations which give rise to optical confinement via the p hotoelastic effect. Model calculations show good agreement with the experim ental data and provide mode profiles for both transverse magnetic and trans verse electric propagation. These experiments contribute to a more detailed understanding of the complex stress and refractive index distributions pre sent in photoelastic semiconductor optical channel waveguide structures, st ructures which are potentially useful for optical device technology. (C) 20 01 American Institute of Physics.