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Plasmonics

Can graphene on silicon chips detect 2 μm light fast and well?

Guo J, Li J, Liu C, et al. · Light, science & applications · 2020

Open access · cc by · source: Europe PMC

A thin silicon waveguide topped by graphene and a wide metal strip absorbs light mostly in the graphene, giving fast chip-based detectors beyond the usual telecom band.

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Study at a glance

Design
Other — Mode-solver design of a thin-silicon hybrid plasmonic waveguide, then fabrication and measurement of photocurrent maps, responsivity and frequency response for three devices on one chip.
N
Device experiment; results reported for three devices (A, B, C) on the same chip, not a sample.
Population
Monolayer-graphene photodetectors on silicon-on-insulator hybrid plasmonic waveguides operating at 2 and 1.55 micrometres
Outcome
Graphene absorption fraction, photoresponse mechanism versus gate and bias voltage, responsivity, and 3 dB bandwidth

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

Thinning the silicon core roughly doubled absorption, and the design put about 70% of absorbed light into graphene. At zero bias the photocurrent flipped sign with gate voltage, the signature of the photothermoelectric effect; with bias, bolometric or photoconductive effects dominated depending on doping. At 2 μm a device reached about 70 mA/W with bandwidth above 20 GHz, and at 1.55 μm a device reached 396 mA/W with bandwidth above 40 GHz and received 30 Gbit/s data.

Methodology

The authors simulated how silicon ridge width, silicon thickness and metal-strip size change how much guided light is absorbed by graphene versus wasted in the metal, and chose a thin, wide silicon ridge. They fabricated detectors with a top metal signal electrode and metal-graphene-metal ground contacts, mapped photocurrent against gate and bias voltage, and measured responsivity and frequency response at 2 μm, plus a companion device at 1.55 μm.

Limitations

Both bandwidth figures are limited by the lab equipment, so the true speed is unknown. The metal-graphene-metal design has a high dark current, so signal-to-dark ratio and noise-equivalent power are modest, and graphene mobility was low, probably due to fabrication defects. Only three devices on one chip were characterised, with some random variation in contact resistance, so reproducibility is not established. Responsivity at 2 μm remains well below the 1.55 μm device.

How this study connects

Role on claims

Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.

  • SupportsPlasmonic hot electrons and strong couplingconcept

    Working plasmonic detectors often rely on thermal carrier effects.

    Hybrid plasmonic waveguides that concentrate light in graphene gave practical chip photodetectors (396 mA/W and above 40 GHz at 1.55 um; about 70 mA/W at 2 um), with the zero-bias signal attributed to the photothermoelectric effect rather than hot-electron emission.

    Evidence for the claim as stated.

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