Fabrication of SiGe optical waveguides using VLSI processing techniques

The fabrication of rib waveguides in SiGe using the local oxidation of sili con (LOCOS) was investigated. Samples consisted of strained Si.97Ge.(03) or Si.94Ge.06 waveguiding layers with silicon cladding layers. The structural stability of these strained layers during thermal cycling up to 1050 degre esC was examined using X-ray rocking curve analysis, scanning electron micr oscopy, and Nomarski microscopy of etched samples. Since single SiGe layers sufficiently thick to support optical waveguiding are typically above the equilibrium critical thickness, dislocation formation during high-temperatu re processing is unavoidable. This work concentrated on minimizing these di slocations, It was found that the dislocation density induced by the proces sing can be minimized by using a strain-compensating mask layer as a barrie r to oxidation, For a specified thermal oxide layer thickness, higher oxida tion temperatures were found to minimize the dislocation density relative t o oxidation at temperatures closer to the metastable Limit, Furthermore, th e large birefringence found in all strained-layer SiGe waveguides is signif icantly reduced after LOGOS processing, These effects were used to fabricat e the first reported optical waveguides and photonic devices in SiGe using standard VLSI-type processing. The device is a 1.3/1.55-mum duplexer with w avelength isolation of roughly 10 dB.