Emmanuel Lhuillier
Sorbonne Université, CNRS, Institut des NanoSciences de Paris, INSP, 75005 Paris, France.

Designing light matter coupling in nanocrystal array used for infrared sensing

Nanocrystals are one of the few exemple of nanomaterials to have reached a mass market with their use as green and red source in display. Interest for their infrared properties have first been driven by solar cell, but currently this is th ease to shift their absorbance further in the infrared that focus the interest for this class of material. In the introduction, i will first review some recent developments relative to HgTe nanocrystals [1] from their synthesis to their device integration including infrared LED [2] and focal plane array for imaging.
One key issue raised by the use of nanocrystal for photoconduction is the discrepency between the absorption depth (few µm) and the charge diffusion length (<100 nm). In other word, thick samples are desirable to absorb photon, but photocarrier collection remains limited. To overcome issue, we have tackle the issue by both side. We design very short size (<100 nm) devices that match the diffusion length and show that in this case electronic transport is dramatically improved [3]. The other strategy deals with the introduction of sub wavelength resonator which role is to « focus » the light onto a thin slab of semiconductor (<200 nm) [4-6]. Such device are able to achieve broadband absorption (≈80 % of incident light) in the short wave infrared.

[1] Mercury Chalcogenide Quantum Dots: Material Perspective for Device Integration, C Gréboval et al, Chem. Rev. (2021)
[2] Electroluminescence from HgTe Nanocrystals and its Use for Active Imaging, J Qu et al, Nano Lett. 20, 6185 (2020)
[3] Infrared photoconduction at the diffusion length limit in HgTe nanocrystal arrays, A Chu et al, Nature Commun. 12, 1794 (2021)
[4] Complex Optical Index of HgTe Nanocrystal Infrared Thin Films and Its Use for Short Wave Infrared Photodiode Design, P Rastogi et al, Adv. Opt. Mat., 2002066 (2021)
[5] Pushing absorption of perovskite nanocrystals into the infrared, P Rastogi et al, Nano Lett. 20, 3999 (2020)
[6] Near Unity Absorption in Nanocrystal Based Short Wave Infrared Photodetectors using Guided Mode Resonators, A Chu t al, ACS Photonics 6, 2553 (2019)