Optical properties of pseudomorphic Si1-xGex for Si-based waveguides at the λ=1300-nm and 1550-nm telecommunications wavelength bands

The index of refraction for pseudomorphic Si_1-xGe_x layers grown on Si has been measured at wavelengths λ=1310 mn and λ=1550 nm. The refractive index values were obtained from waveguide mode profile measurements on a series of Si-Si_1-xGe _x-Si waveguides with Ge_x concentrations between x=0.01 and x=0.1. The index of refraction, n, is significantly larger for light polarized parallel to the growth direction than for light polarized in the plane of the epilayer. This birefringence is consistent with the anisotropic index change predicted using photoelastic theory, given the biaxial strain present in the pseudomorphic Si_1-xGe _x layers. At all wavelengths and polarizations, n varies linearly with the Ge concentration. The pseudomorphic Si_1-xGe _x waveguides layer are stable against lattice relaxation during short anneals at 950°C, but exhibit partial relaxation after annealing at 1200°C