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Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna


A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise1,2,3,4. A photodetector can be made smaller by using a subwavelength active region; however, this can result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a half-wave Hertz dipole antenna (length 380 nm) from radio waves, but at near-infrared wavelengths (length 1.3 µm), to concentrate radiation into a nanometre-scale germanium photodetector. This gives a polarization contrast of a factor of 20 in the resulting photocurrent in the subwavelength germanium element, which has an active volume of 0.00072 µm3, a size that is two orders of magnitude smaller than previously demonstrated detectors at such wavelengths.

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Figure 1: A schematic of the device.
Figure 2: FDTD-simulated optical near-field intensity 25 nm above the substrate surface.
Figure 3: Scanning electron microscopy (SEM) images of the fabricated devices.
Figure 4: Bias voltage dependence of an antenna detector.
Figure 5: Measured photocurrent responses for light polarization in the y and x directions.


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This work was supported by the Air Force Office of Scientific Research (AFOSR) Multi University Research Initiative (MURI) ‘Plasmon Enabled Nanophotonic Circuits’, and Microelectronics Advanced Research Corporation (MARCO)/Defense Advanced Research Projects Agency (DARPA) Interconnect Focus Center. We also acknowledge the support of the Office of Technology Licensing (OTL) Stanford Graduate Fellowship.

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Correspondence to Liang Tang.

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Tang, L., Kocabas, S., Latif, S. et al. Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna. Nature Photon 2, 226–229 (2008).

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