Index of Refraction and Strain Induced Birefringence of Pseudomorphic Si1-xGex

The index of refraction of pseudomorphic Si1-xGex layers grown on Si has been determined at wavelengths 7n=1330 nm and 7n= 1550 nm, for Ge concentrations between x=0.01 and x=0.1. The refractive index values were obtained from mode profile measurements on a series of Si1-xGex waveguides. The index of refraction 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 photoelelastic theory, given the biaxial strain present in the pseudomorphic Si1-xGex layers.