Si0.5Ge0.5 relaxed buffer photodetectors and low-loss polycrystalline silicon waveguides for integrated optical interconnects at lambda=1.3 mu m

Silicon based photonic circuits are an attractive option for future generations of microprocessors, if standard VLSI electronics can be coupled with on chip optical interconnects and photodetectors for information transfer and clock distribution. A silicon, VLSI compatible, integrated waveguide-photodetector technology for operation at lambda = 1.3 mu m is presented. Functionality at 1.3 mu m permits the use of Si/SiO2 waveguides and offers compatibility with short-haul silica fiber optic systems. These waveguides have a large index contrast (Delta n = 2) thus offering superior optical confinement in strip waveguides with dimensions as small as 0.5 mu m by 0.2 mu m. The strong confinement and these small dimensions allow high interconnect line densities without cross-talk or RC delay concerns. We measure optical losses in polysilicon waveguides as low as 13 dB/cm at lambda = 1.3 mu m using an optical cutback technique. A completely relaxed Si0.5Ge0.5 buffer with low threading dislocation density (similar to 10(6) cm(-2)) is used as an epitaxial template for a P-I-N photodetector. The relaxed buffer is grown at 815 degrees C with ultra high vacuum chemical vapor deposition (UHV-CVD) using a composition graded layer technique with a grading rate of 10%Ge/mu m. We measure carrier collection efficiencies of 50% and responsivity of 3 mA/W. A beam propagation model is used to determine an effective absorption length less than 2 mu m in photodetectors butt-coupled to polySi waveguides.