Monolithic Integration of Top Si3N4 - Waveguided Germanium Quantum-Dots Microdisk Light Emitters and PIN Photodetectors for On-chip Ultrafine Sensing

Using a coordinated combination of lithographic patterning and self-assembled growth, Ge spherical quantum-dots (QDs) were controllably generated within host $Si_{3}N_{4}$ layers as active medium for Si photonics. A significant fabrication advantage of our approach is the high-temperature thermal stability of Ge QDs that are formed by thermal oxidation of poly-SiGe at $900^{o}C$, offering process flexibility in the waveguide-material choices and device designs. Our Ge QDs enable monolithic integration of $\mu$ disk light-emitters and PIN photodetectors (PDs) with top $Si_{3}N_{4}$/SiO 2 /Ge waveguide-coupled structures using standard Si processing. Over 95% coupling efficiency from SiN WGs to Ge QD PDs is achievable. Ultralow dark current of $0.1 pA/\mu m$, high responsivity of 3,500 A/W at 850 nm and 10A/W at 1550 nm, 3dB frequency $\gt10$ GHz for Ge-QD PDs and low threshold power of $0.6 kW/cm^{2}$ for optically-pumped Ge QD/SiN $\mu$ - disks lasing evidence the high degree of crystallinity of our Ge QDs as an effective building block for 3D SiN PICs.