Institut des
NanoSciences de Paris
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Infrared optoelectronic using nanocrystals

Emmanuel Lhuillier

The group is involved in the design of infrared optoelectronics devices using narrow band gap nanocrystals as active materials. This research topic is highly pluridisciplinar with

Nanocrystals synthesis, including the development of new growth method.

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Image of nanocrystal synthetic setup

For example, we report the first highly concentrated synthesis of HgTe nanocrystals by swicthing from conventional mercury salts to liquid mercury as precursor. We thus obtained the most concentrated synthesis of HgTe nanpocrystal ever reported with concentration close to 100 g/L. This new synthetic route is promissing to achieve greener synthesis of HgTe with reduced exposure of work force to Hg precursor.

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Scheme of liquid Hg based synthesis of Hgte nanocrystals

We have also been the first to report nanocrystals with THz absorption. A new synthetic procedure has enable the growth of nanocrystal with size above the Bohr radius, thus enabling absorption up to 100 µm. This work demonstrated the possibility to tune the absorption of HgTe nanocrystal all over the infrared from 1 to 100 µm.

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Infrared spectra of HgTe nanocrystals with various sizes

Related publications

- 1. Near to Long Wave Infrared Mercury Chalcogenide Nanocrystals from Liquid Mercury, N. Goubet et al, J Phys Chem C 124, 8423 (2020)
- 2. Intraband mid infrared transitions in Ag2Se nanocrystals : potential and limitations for Hg-free low cost photodetection, J. Qu et al, J. Phys Chem C 122, 18161 (2018)
- 3. Terahertz HgTe nanocrystals : beyond confinement, N. Goubet et al, J. Am. Chem. Soc. 140, 5053 (2018).
- 4. Wavefunction engineering in HgSe/HgTe colloidal heterostructures to enhance mid infrared photoconductive properties, N. Goubet et al, Nano Lett 18, 4590 (2018)

Device fabrication using clean room and air free processing in glove box

We benefit from INSP clean room, as well as access to « Paris centre clean room consortium » giving us access to optical, laser and e-beam lithography. We also have possibilities to deposit metals and dielectrics including high-k materials. In the group, we also have glove-box for air free processing of nanocrystals. This also includes an evaporator connected to the glove box for full air free fabrication of device.

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Image of setup for air free processing

Investigation of the material electronic structure

Devices integration necessary requires a deep knowledge on the material electronic structure. Our main builiding block is HgTe nanocrystal which combine bulk inverted band structure with quantum confinement and surface chemistry dependence. It is thus of utmost importance to unveil band alignement of this material in absolute energy scale to be able to efficiently integrate it into devices with the right band alignment (low Schottky barrier). To reach this goal, we use a combination of infrared spectroscopy and photoemission (mostly conducted on tempo beamline of synchrotron Soleil). We also use time-resoved photoemission which is a precious tool to probe carrier relaxation dynamics as well as surface band bending.

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Photo of tempo beamline at Soleil

Related publications

- 5. Effect of pressure on interband and intraband transition of mercury chalcogenides quantum dots, C. Livache et al, J. Phys Chem C 123, 13122 (2019)
- 6. Revealing the Band Structure of FAPI Quantum Dot Film and its Interfaces with Electron and Hole Transport Layer using Time Resolved Photoemission, D. Amelot et al, J Phys Chem C 124, 3873 (2020)
- 7. Design of Unipolar Barrier for Nanocrystal Based Short Wave Infrared Photodiode, A. Jagtap et al, ACS Phot. 5, 4569 (2018) Charge dynamics and optolectronic properties in HgTe colloidal quantum wells, C. Livache et al, Nano Lett 17, 4067 (2017).

Electronic transport with gate, temperature and time resolved possibilities

Device performance directly relates to their transport properties. Investigation of the transport is thus a central topic in the group. We have develloped instrument to conduct measurement with Fermi level (ie with gate) and temperature witha resolution down to sub fA. We are also equipped to conduct photoconduction measurements (from UV to mid IR) with spectral and time resolved experiments. The instruments used to measured transport are not limited to nanocrystals fo HgTe and we also explore other materials such as TMDC, germanane, and other nanomaterials.

Related publications

- 8. A Colloidal Quantum Dot Infrared Photodetector and its use for Intraband Detection, C. Livache et al, Nature Comm 10, 2125 (2019)
- 9. Field effect transistor and photo transistor of narrow band gap nanocrystal arrays using ionic glasses, C. Gréboval et al, Nano Lett 19, 3981 (2019)

Design of the light matter coupling to achieve high absoprtion and spectral shaping

A central point in the design of infrared sensor using nanocrystal is the tradeoff between absorption and carrier transport. Absorption pushed toward thick film (1 µm and more) but this is incompatible with the short carrier diffusion length resulting from hopping transport. By integrating plasmonic resonator, such as guided mode resonator, we are able to focus the light on a thin slab of semiconductor and achieve absorption close to unity. This strategy can also be used to design on demand absorption spectral or to offer spectral tunability beyond the material quantum confinement.

Related publications

- 10. Near Unity Absorption in Nanocrystal Based Short Wave infrared Photodetector using Guided Mode Resonator, A. Chu et al, ACS Photonics 6, 10, 2553-2561 (2019)
- 11. Pushing absorption of perovskite nanocrystals into the infrared, P. Rastogi et al, Nano Lett 20, 3999 (2020)

Integration of nanocrystals for the fabrication of infrared imaging system

Nanocrystals offer great promissises as low-cost alternative to epitaxially grown infrared absorpbing semiconductor. This is especially true in the short wave infrared, where the cost of current sensor remains uncompatible with many new infrared applications such as industrial vision. In collaboration with New Imaging Technologies, we design short wave infrared focal plane array where nanocrystal are used to functionalize a CMOS read out circuit to obtain short wave infrared photoconduction

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Image made with HgTe nanocrystals based sensor

Related publications

- 12. HgTe Nanocrystals for SWIR Detection and their Integration up to Focal Plane Array, A. Chu et al, ACS Appl. Mater. Interfaces 11, 33116 (2019).
- 13. HgTe Nanocrystal Inks for Extended Short Wave Infrared Detection, B. Martinez et al, Adv Opt Mat 7, 1900348 (2019)

Infrared light emission

The group also works on light emission in geometrical LED geometry using nanocrystals as light emitter. Our interest goes beyond just the LED performance and we integrate LED for active imaging. In the infrared, the reflexion constrats can be quite different from the visible and this can be used for moisture detection for example, see the figure below.

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Left scheme of an infrared LED based on HgTe Nanocrystals. right scheme of a biscuit presenting a moisture strain that clearly appears under IR illumination while this stain presents no contrast in the visible

Related publications

- 15. Electroluminescence from HgTe Nanocrystals and its Use for Active Imaging, J. Qu et al, Nano Lett 20, 6185 (2020)
- 16. A nanoplatelet-based light emitting diode and its use for all-nanocrystal LiFi-like communication, J. Qu et al, ACS Appl Mater Interfaces 12, 22058 (2020)


Main collaborations

- ESPCI – Sandrine Ithurria
- Synchrotron Soleil on Tempo (Mathieu Silly) and Smis (francesco Capitani) beamlines
- Onera – Greogory Vincent
- New Imaging Technologies