nano-LED could support multi-Gbit/s on chip traffic

February 03, 2017 // By Julien Happich
Photonics is a hot topic when it comes to increasing inter-chip and on-chip traffic between different processor or memory blocks. So far, microwaveguides, light modulator, outcoupling gratings and photodetectors have been successfully integrated, but designing suitable micro-scale light sources has proved to be challenging.

In a paper titled "Waveguide-coupled nanopillar metal-cavity light-emitting diodes on silicon" just published in Nature Communications, researchers from the Eindhoven University of Technology demonstrated a nano-scale III–V LED layer stack bonded to a silicon substrate and coupled to an InP-membrane waveguide leading to a grating coupler.

SEM-picture of the new nano-LED showing the fabricated device structure before metallization. The nanopillar LED lies on top of a waveguide connected to a grating coupler.

Taking the shape of a sub-micron sized nano-pillar, the nano-LED was characterized to be 1000 times more efficient than its predecessors, with an output power in the order of a few nW at room temperature, compared to outputs in pW reported in literature. According to the paper, the device showed a relatively high on-chip external quantum efficiency (10 −4 to 10 −2 for room-temperature and 9.5 K, respectively).

At low temperature, the researchers reported a power level above 50nW, corresponding to over 400 photons per bit at 1Gb/s, "far above the shot-noise limited sensitivity of an ideal receiver", they wrote. Working at telecommunications wavelengths (1.55 μm), the device was successfully modulated using a pulse pattern generator at frequencies up to 5GHz.

Schematic representation of the nanopillar LED on a silicon substrate. The layer stack from top to bottom is: n-InGaAs(100 nm)/n-InP(350 nm)/InGaAs(350 nm)/p-InP(600 nm)/p-nGaAsP(200 nm)/InP(250 nm)/SiO 2/BCB/SiO2/Si.

"With the expected low loss of short-distance interconnects and continuous progress in integrated receivers, this power level may enable intrachip data communications with an ultracompact source", they note.

The researchers have also developed a surface passivation method that could further boost the efficiency of the nano-LED 100-fold, while energy consumption could be further reduced by improving the ohmic contacts.

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