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Using a coordinated combination of lithographic patterning and self-assembled growth, Ge spherical quantum dots (QDs) were controllably generated within host layers of Si 3 N 4 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 lithographically patterned structures at 800 • C-900 • C, offering flexibility in the waveguide (WG)-material choices, co-design, and integration of Ge photonic devices. Our Ge QDs enable monolithic integration of microdisk light emitters and p-i-n photodetectors (PDs) with top-Si 3 N 4 WG-coupled structures using standard Si processing. Low dark current of 0.3 mA/cm 2 at 300 K and 0.2 µA/cm 2 at 77 K in combination with 3-dB frequency of 12 GHz for Ge-QD PDs and low threshold power of 0.6 kW/cm 2 for optically pumped Ge QD/SiN microdisks light emission evidence the high degree of crystallinity of our Ge QDs being an effective building block for 3-D SiN photonic integrated circuits. Index Terms-Ge, microdisks, photodiodes (PDs), quantum dot (QD), top-Si 3 N 4 waveguides (WGs).

Beginning with our exciting discovery of germanium (Ge) spherical quantum-dot (QD) formation via the peculiar and symbiotic interactions of Si, Ge, and O interstitials, we have embarked on a journey of vigorous exploration, creating unique configurations of self-organized Ge-QDs/Si-containing layers. Our aim is to generate advanced Ge-QD photonic devices, while using standard, mainstream Si processing techniques. This paper summarizes our portfolio of innovative Ge-QD configurations. With emphasis on both controllability and repeatability, we have fabricated size-tunable, spherical Ge-QDs that are placed at predetermined spatial locations within Si-containing layers (SiO2, Si3N4, and Si) using a coordinated combination of lithographic patterning and self-assembled growth. We have successfully exploited the multi-dimensional, parameter spaces of process conditions in combination with layout designs to achieve exquisite control available through the thermal oxidation of lithographically patterned, poly-Si1 − xGex structures in close proximity with Si3N4/Si layers. In so doing, we have gained insight into the growth kinetics and formation mechanisms of self-organized, Ge spherical QDs embedded within SiO2, Si3N4, and Si layers, respectively. Our Ge-QD configurations have opened up a myriad of process/integration possibilities including top-to-bottom evanescent-wave coupling structures for SiN-waveguided Ge-QD photodetectors and Ge-QD light emitters for Si photonics within Si3N4 integrated photonics platforms for on-chip interconnects and sensing.

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We report experimental fabrication and characterization of photoMOSFETs with self-aligned gatestacking heterostructures of indium-tin-oxide (ITO)/Ge nanospheres/SiO2-shell/Si1-xGex-nanosheets. Array of Genanosphere/SiO2-shell/SiGe-nanosheet heterostructures was created in a self-organized, CMOS approach using the thermal oxidation of lithographically-patterned poly-Si0.85Ge0.15 nanopillars over buffer layers of Si3N4 on top of SOI substrates. With a polysilicon dummy-gate, source and drain self-align with the transparent ITO gate using a replacement-metal-gate process. Very high photocurrent gain, large photoresponsivity, as well as improved input capacitance and 3dB frequency were experimentally achievable in our photoMOSFETs. The pivotal roles of Ge-optical gate and SiGe-channel for large photoresponsivity and current gains were analyzed via numerical simulation.