# High efficiency resonant-metasurface germanium photodetector with ultra-thin intrinsic layer

## TL;DR

This paper demonstrates a resonant-metasurface germanium photodetector with ultra-thin intrinsic layer achieving high efficiency and 20 Gbps speed, promising low-cost, high-speed optical detection for telecommunications.

## Contribution

It introduces the first normal incident resonant-metasurface germanium photodetector with ultra-thin intrinsic layer, enhancing efficiency and bandwidth through trapped-mode resonances.

## Key findings

- External quantum efficiency >60% at 1550 nm
- Enhanced absorption by over 300% due to resonances
- Potential for >50 GHz bandwidth with smaller device size

## Abstract

Photodetectors at telecommunications-band with high efficiency and high speed are becoming increasingly important as the booming of big data, 5G, internet of things, cloud computing, artificial intelligence and relevent applications. Silicon-based Germanium photodetectors exhibit great potential in reducing the cost and power dissipation, due to its compatibility of monolithic integration with signal-processing electronics. We report the first demonstration of normal incident resonant-metasurface germanium photodetector, to address the trade-off between quantum efficiency, bandwidth and wavelength coverage for free-space detectors. With an ultra-thin intrinsic layer thickness of 350 nm, a high external quantum efficiency of more than 60% and clearly open eyes at the speed of 20 Gbps are achieved, for a 30 {\mu}m-diameter device. The photodetector employs multiple trapped-mode resonances to enhance the localized electromagnetic field, which not only enhances the external quantum efficiency by more than 300% at 1550 nm, but also extends to the whole C band. Further simulation and measurement with small incident spot size show the feasibility to achieve >50 GHz 3 dB bandwidth by simply reducing the mesa size, with minor sacrifice of the enhanced absorption. This work paves the way for the future development of low-cost, high efficiency normal incident germanium photodetectors operating at data rates of 50 Gbps or higher.

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Source: https://tomesphere.com/paper/1904.05744