Enhanced photodetection

David Miller and his colleagues investigated several approaches for enhancing photodetection using nanometallic structures. These include the use of apertures, antennas, and waveguides to concentrate light into deeply subwavelength structures that can have potential benefits of both good sensitivity and very low device capacitance. Such low capacitance can further enhance the usefulness of that concentration.

This work includes nanometallic apertures to concentrate light into small detector areas [1][2], including integration with CMOS electronics [2], the equivalent of a Hertz dipole antenna to concentrate into a deeply subwavelength detector element [3], and the use of nanometallic waveguides [4] to route effectively over ~ 10 micron distances into photodetectors. Other work includes using nanometallic slots specifically designed to use lateral Fabry-Perot type resonances to give tuned absorption response [5] and to enhance germanium photodetection response [6] for longer telecommunications wavelengths. (See also Nanometallic resonant detectors.)

Nanometallic and plasmonic structures can be very effective in concentrating light into deeply subwavelength structures. Often, however, there is significant power loss involved when using such metallic structures because of dissipation in the metals. That power loss can reduce or even eliminate the benefit of the concentration. For photodetectors, however, reducing the volume of the detector also reduces its capacitance. In a well integrated detector/amplifier system, that can mean that smaller optical input energy is required to generate a specific signal voltage at the amplifier input, and the overall optical energy required to generate that signal voltage can be reduced in proportion to the reduction in total capacitance. Suppose, for example, that a nanometallic concentrating structure had a power loss of a factor of 2 in concentrating the light into a subwavelength photodetector, but that the resulting device capacitance was reduced by a factor of 10 because of the reduced device size. Then we could have an overall benefit of a factor of 5 in the signal voltage generated for a given input optical energy. Hence, concentration of light into sub-wavelength photodetectors is one application where the overall system performance might still benefit despite large optical power losses in the nanometallic concentrating structure.

The concept of nanometallic concentration from the micron scales of optical waveguides to ~ 100 nm scales of intimately integrated detectors is considered in a “straw-man” proposal for advanced low-energy optically interconnected systems in [7].

[1] L. Tang, D. A. B. Miller, A. K. Okyay, J. A. Matteo, Y. Yuen, K. C. Saraswat, and L. Hesselink, “C-shaped nanoaperture-enhanced germanium photodetector,” Opt. Lett. 31, 1519-1521 (2006)

[2] L. Tang, S. Latif, and D. A. B. Miller, “Plasmonic device in silicon CMOS,” Electronics Lett. 45, 706 – 708 (2009)

[3] L. Tang, S. E. Kocabas, S. Latif, A. K. Okyay, D.-S. Ly-Gagnon, K. C. Saraswat and D. A. B. Miller, “Nanometre-Scale Germanium Photodetector Enhanced by a Near-Infrared Dipole Antenna,” Nature Photonics 2, 226 – 229 (2008) https://doi.org/10.1038/nphoton.2008.30

[4] D.-S. Ly-Gagnon, K. C. Balram, J. S. White, P. Wahl, M. L. Brongersma, and D. A. B. Miller, “Routing and Photodetection in Subwavelength Plasmonic Slot Waveguides,” Nanophotonics 1, 9–16, (2012) https://doi.org/10.1515/nanoph-2012-0002

[5] K. C. Balram and D. A. B. Miller, “Self-aligned silicon fins in metallic slits as a platform for planar wavelength-selective nanoscale resonant photodetectors,” Opt. Express 20, 22735-22742 (2012)

[6] K. C. Balram, R. M. Audet, and D. A. B. Miller, “Nanoscale resonant-cavity-enhanced germanium photodetectors with lithographically defined spectral response for improved performance at telecommunications wavelengths,” Opt. Express 21, 10228-10233 (2013)

[7] D. A. B. Miller, “Attojoule Optoelectronics for Low-Energy Information Processing and Communications: a Tutorial Review,” IEEE/OSA J. Lightwave Technology 35 (3), 343-393 (2017) https://doi.org/10.1109/JLT.2017.2647779; http://ieeexplore.ieee.org/document/7805240/