Abstract

Here, we propose a waveguide-integrated germanium plasmonic photodetector operating simultaneously at bandwidth exceeding 100 GHz and responsivity above 1 A/W. The proposed photodetector takes advantage of a long-range dielectric-loaded surface plasmon polariton waveguide configuration. As this configuration ensures a long propagation distance (i.e., small absorption into metal) and a good mode field confinement (i.e., high interaction of the electric field with a germanium material), it is perfect for the realization of plasmonic germanium photodetectors. Such a photodetector, even without optimization, provides a responsivity exceeding 1 A/W for wavelengths of 1310 and 1550 nm. To achieve such a responsivity, only a 5 μm long waveguide is required for 1310 nm and a 30 μm long waveguide for 1550 nm. With optimization, this value can be highly improved. In the proposed arrangement, a metal stripe simultaneously supports a propagating mode and serves as one of the electrodes, while the second electrode is located a short distance from the waveguide. As a propagating mode is tightly confined to the germanium ridge, the external electrode can be placed very close to the waveguide without disturbing it. As such, the distance between electrodes can be smaller than 350 nm, which allows one to achieve a bandwidth exceeding 100 GHz. However, as most of the carriers are generated inside a distance of 100 nm from a stripe, a bandwidth exceeding 150 GHz can be achieved for a bias voltage of $-4\mathrm{V}$.

© 2019 Optical Society of America

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