Lin C.-HHuang D.-WShih T.-TKuo H.-CChang S.-W.DING-WEI HUANG2021-09-022021-09-02202110944087https://www.scopus.com/inward/record.uri?eid=2-s2.0-85103098497&doi=10.1364%2fOE.414691&partnerID=40&md5=f719ce47c2e5578438e945342a7a134ahttps://scholars.lib.ntu.edu.tw/handle/123456789/580780The external bandwidth of germanium waveguide photodetectors (PDs) decreases with the device length due to the load and parasitic effects even if the internal one is less affected. Shortening PDs raises the external bandwidth but lowers the responsivity, introducing a trade-off between the two figures of merits. Here, we present a scheme of waveguide PDs based on total internal reflections of corner reflectors. The reflector can be easily fabricated with the standard photolithography at the end of PDs to efficiently reflect optical power back to germanium for additional absorption, allowing for further size reduction. The structure may render the optimization of PDs more flexible. ? 2021 Optical Society of America under the terms of the OSA Open Access Publishing AgreementBandwidth; Economic and social effects; Germanium; Photons; Reflection; Refractive index; Waveguides; Corner reflector; Figures of merits; Germanium waveguide photodetectors; Optical power; Parasitic effect; Size reductions; Standard photolithography; Total internal reflections; Photodetectorsjournal article10.1364/OE.414691338201722-s2.0-85103098497