The present invention relates to the field of photonics and more particularly to a photodetector.
Photodetectors convert optical signals into electrical signals and are typically used in receivers. To increase sensitivity of a receiver, it would be desirable to provide a photodetector with high responsivity, high speed (bandwidth) and low dark leakage current.
Accordingly, in a first aspect, the present invention provides a photodetector including an interferometer and a photodetection region coupled to the interferometer. The interferometer is configured to generate an optical intensity distribution that corresponds to an electric field distribution in the photodetection region.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the scope of the invention.
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In the embodiment shown, the photodetector 10 includes a waveguide 16 and 5 the interferometer 12 is coupled between the waveguide 16 and the photodetection region 14. Light is guided into the photodetector 10 from waveguide 16. In this manner, the waveguide 16 serves as an incoming waveguide and may be a single-mode waveguide.
In the present embodiment, the photodetection region 14 includes a substrate 18 and an absorption region 20 provided on the substrate 18, the substrate 18 and the absorption region 20 having opposite polarities. The substrate 18 may be formed of silicon (Si) and the absorption region 20 may be provided on the substrate 18 by growing an absorption layer comprising a material such as germanium (Ge) on the silicon substrate 18. This enables absorption of light in the near-infrared wavelength range. One or both the substrate 18 and the absorption region 20 may be formed as a mesa. A first contact region 22 and a second contact region 24 of the photodetection region 14 may be formed by doping the the substrate 18 and the absorption region 20 to form a p-type doping region and an n-type doping region. The first and second contact regions 22 and 24 may be connected to metal electrodes (not shown).
The interferometer 12 is configured to generate an optical intensity distribution that corresponds to an electric field distribution in the photodetection region 14. The interferometer 12 may be a multi-mode interferometric waveguide. Before reaching the photodetection region 14, light first passes through the multi-mode interferometer 12. This excites multiple optical modes, resulting in a pre-determined distribution of regions 25 with high and low optical power intensities within the multi-mode interferometer 12 and in the photodetection region 14. The multi-mode interferometric waveguide may be designed such that regions of high optical intensity occur only at specific regions within the absorption region 20 where the electric field is sufficiently strong so as to maximize the transit-time-limited bandwidth of the photodetector 10. Advantageously, by maintaining a high enough electric field in regions with high optical intensity, transit-time-limited bandwidth is increased. The local electric field intensity within the absorption mesa 20 may also be engineered for optimum performance.
In an embodiment where the absorption region 20 is formed of germanium (Ge), the doped region 24 may be set at a distance from a perimeter of the absorption region 20. In germanium photodetectors, due to the small bandgap of germanium and the high density of surface states, a distance may be left from the edge of the doping region 24 to the edge of the absorption mesa 20 around the perimeter of the absorption mesa 20 to reduce the dark leakage current of the photodetector 10.
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While preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to the described embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the scope of the invention as described in the claims.
Further, unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising” and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
Number | Date | Country | |
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62592426 | Nov 2017 | US |