M. Robillard et al., STRAIN-INDUCED BIREFRINGENCE IN SI1-XGEX OPTICAL WAVE-GUIDES, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 16(4), 1998, pp. 1773-1776
For the design of Si1-xGex optical waveguide devices, one of the most
important material parameters is the refractive index difference, delt
a n, between the alloy layer and the silicon substrate. We have measur
ed delta n for pseudomorphic waveguide layers with germanium fractions
between 1% and 9% by fitting measured mode profiles to theoretical mo
de shapes for a wavelength of 1.3 mu m. For transverse electric modes,
the measured delta n varied with composition as delta n = (0.34+/-0.0
5)x. Transverse magnetic modes were more tightly confined to the waveg
uide layer and the index was determined to be delta n = (0.55 +/- 0.05
)x. The large difference between the two polarizations results from st
rain-induced birefringence. Bulk photoelastic theory, using constants
appropriate for pure silicon, predicts strain contributions to the ind
ex of -0.080x and +0.095x for light polarized parallel and perpendicul
ar, respectively, to the substrate plane, consistent with experimental
observations. (C) 1998 American Vacuum Society.