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This paper presents a novel germanium gated NMOS phototransistor integrated on a silicon photonics platform on silicon-on-insulator (SOI) substrate. The phototransistor is fabricated with a modified NMOS process flow, with germanium which is recrystallized using rapid melt growth during the source/drain activation anneal step. The resulting device, with 1-μm channel length, and 8-μm channel width, demonstrates a responsivity of over 18 A/W at 1550 nm with 583 nW of incident light. By increasing the incident power to 912 μW, the device operates at 2.5 GHz. Miniaturization is expected to improve both responsivity and speed in future devices.

Abstract:We propose a cladding engineering method that flexibly modifies the radiation patterns and rates of metal-clad nanoscale optical cavity. Optimally adjusting the cladding symmetry of the metal-clad nanoscale optical cavity modifies the modal symmetry and produces highly directional radiation that leads to 90% coupling efficiency into an integrated waveguide. In addition, the radiation rate of the cavity mode can be matched to its absorption rate by adjusting the thickness of the bottomcladding layer. This approach optimizes the energy-flow rate from the waveguide and maximizes the energy confined inside the nanoscale optical cavity.

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We present a novel waveguide coupling scheme where a germanium diode grown via rapid melt growth is wrapped around a silicon waveguide. A 4 fF PIN photodiode is demonstrated with 0.95 A/W responsivity at 1550 nm, 6 nA dark current, and nearly 9 GHz bandwidth. Devices with shorter intrinsic region exhibit higher bandwidth (30 GHz) and slightly lower responsivity (0.7 A/W). An NPN phototransistor is also demonstrated using the same design with 14 GHz f(T).