Self-aligned transparent-gate ITO/Germanium nanospheres/SiO2/SiGe-nanosheets photoMOSFETs on silicon nitride platform

We report experimental fabrication and characterization of photoMOSFETs with self-aligned gate-stacking heterostructures of indium-tin-oxide (ITO)/Ge nanospheres/SiO2-shell/Si1-xGex-nanosheets. Array of Ge-nanosphere/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.