Pushing electroluminescence of nanocrystals beyond telecom wavelengths

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Published on 07 June 2022

Nanocrystals are semiconductor nanoparticles with size tunable optical features. They are now mature enough to be integrated as light sources in displays. In such devices, nanocrystals can be optically excited and used as a light down converter to generate green and red light from a blue light emitting diode (LED) made of InGaN. A more complicated challenge is the use of nanocrystals as active material for LED where they have to be both optically and electrically active. Since the early 2000s, such nanocrystal-based LEDs have been demonstrated in the visible and near infrared range. However, up to now, there are no reports of nanocrystal-based electroluminescence above 1.7 µm. This spectral range corresponds to a technological gap. Indeed, up to telecom wavelengths (1.55 µm) quantum well technologies based on III-V materials provide an efficient and powerful light source, and above 4 µm the quantum cascade laser is now well established. In the middle, only a few systems can be used. A consortium of researchers in Paris has explored the potential of HgTe nanocrystals for electroluminescence above 2 µm.

Their LED stack relies on HgTe nanocrystals as the active medium and this layer is sandwiched between ZnO and PbS layers that are used as electron and hole injectors respectively. The device can be fully fabricated from solution processing. They demonstrate electroluminescence from 2 to 2.3 µm by tuning the HgTe particle size. Their device presents a low threshold voltage close to the optical band gap which reduces the device electrical consumption. Future work will focus on pushing the emission wavelength further into the mid infrared.

More information :
J. Qu et al., “Electroluminescence from nanocrystals above 2 µm,” Nature Photonics 16, 38 (2022)
https://doi.org/10.1038/s41566-021-00902-y and read at https://rdcu.be/cC8AT