First Demonstration of Waveguide-Coupled Ge 0.92 Sn 0.08 /Ge Multiple-Quantum-Well Photodetector on the SOI Platform for 2-μm Wavelength Optoelectronic Integrated Circuit

We report the first demonstration of a silicon-on-insulator (SOI) waveguide-coupled Ge 0.92 Sn 0.08 /Ge multiple-quantum-well (MQW) photodiode (PD) for 2 μm wavelength using a flip-chip bonding technology. The light in the waveguide couples to the PD for detection via a grating coupler. The grating coupler and waveguide were designed and fabricated on the standard SOI wafer for 2 μm and bonded with the GeSn/Ge PDs. On the same wafer, back illuminated GeSn/Ge PDs were also integrated using the same technology for free space optical detection. Our waveguide-coupled PD exhibits responsivity of 10.3 mA/W at 2 μm wavelength and one of the lowest dark current densities of 38.4 mA/cm2 for Ge 1-x Sn x PDs. In addition, no degradation of the dark current was found after the bonding.