SiGeC/Si Electrooptic Modulators

The addition of carbon to silicon-germanium alloys provides the ability to lattice match thick layers with high germanium composition to silicon substrates. Thick strain-free silicon-germanium-carbon (SiGeC) layers on silicon allow the design of optical waveguides that have large optical mode overlap with the waveguide core. In addition, SiGeC/Si heterostructures enable strong confinement of large electron and hole concentrations. The combination of tightly confined carriers and photons can be used to realize high-performance broadband electrooptic modulators based on carrier density-induced refractive index changes. We show that modulators with lengths around 30 mum and turn-on times below 0.2 ns are possible with optimized designs