OCN research

Infrared optoelectronic using nanocrystals

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

Nanocrystal synthesisOptoelectronic devicesElectronic structure investigationFunding

Nanocrystals synthesis, including the development of new growth method.

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.

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

Infrared spectra of HgTe nanocrystals with various sizes

Related publications

Seeded growth of HgTe nanocrystals for shape control and their use for narrow infrared electroluminescence, Y. Prado et al, Chem Mater 33, 2054 (2021)
Near to Long Wave Infrared Mercury Chalcogenide Nanocrystals from Liquid Mercury, N. Goubet et al, J Phys Chem C 124, 8423 (2020)
Terahertz HgTe nanocrystals: beyond confinement, N. Goubet et al, J. Am. Chem. Soc. 140, 5053 (2018).
Wavefunction engineering in HgSe/HgTe colloidal heterostructures to enhance mid infrared photoconductive properties, N. Goubet et al, Nano Lett 18, 4590 (2018)

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 with a 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.

TCO dual gate

Schematic of dual gated pn junction made from nanocrystals

Related publications

Ferroelectric Gating of Narrow Band-Gap Nanocrystal Arrays with Enhanced Light Matter Coupling, C. Gréboval, et al, ACS Phot 8, 259 (2021)
Infrared Photoconduction at the Diffusion Length Limit in HgTe Nanocrystal Array, A. Chu, et al, Nature commun 12, 1794 (2021)
Field effect transistor and photo transistor of narrow band gap nanocrystal arrays using ionic glasses, C. Gréboval, et al, Nano Lett 19, 3981 (2019)
Reconfigurable 2D/0D p-n Graphene/HgTe nanocrystal heterostructure for Infrared detection, U. N. Noumbé, et al, ACS Nano 14, 4567 (2020)

Design of the light matter coupling to achieve high absorption 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.

Scheme of a device coupling light resonator and nanocrystal to achieve broadband infrared sensing-Picture has been selected as cover of Advanced Optical Materials.

Related publications

Bias reconfigurable photoresponse of infrared nanocrystal film integrated into a coupled nano Fabry Perot resonator, H. Dang et al, ACS photonics (2023)
Nanocrystal based Active Photonics Device through Spatial Design of Light-Matter Coupling, T. H. Dang, et al, ACS photonics (2022)
Broadband enhancement of mid-wave infrared absorption in a multi resonant device, T. H. Dang et al, Adv Opt Mater 10, 2200297 (2022).
Guided mode resonator coupled with nanocrystal intraband absorption, A. Khalili et al, ACS Photonics 9, 985 (2022)
Pushing absorption of perovskite nanocrystals into the infrared, P. Rastogi et al, Nano Lett 20, 3999 (2020)
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)

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.

A video highlighting the transformation of nanocrystal solution into infrared camera

Related publications

Photoconductive focal plane array based on HgTe quantum dots for fast and cost-effective short-wave infrared imaging, C. Gréboval et al, Nanoscale (2022).
Material Perspective on HgTe Nanocrystal-based Short Wave Infrared Focal Plane Arrays, H. Zhang et al, Chem Mater 34, 10964 (2022)
HgTe Nanocrystals for SWIR Detection and their Integration up to Focal Plane Array, A. Chu et al, ACS Appl. Mater. Interfaces 11, 33116 (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 constrast can be quite different from the visible and this can be used for moisture detection for example, see the figure below.

toc LED 2um

Left scheme of an infrared LED based on HgTe Nanocrystals.

Related publications

Electroluminescence from Nanocrystals above 2 µm, J. Qu et al, Nature Phot. 16, 38 (2021).
Optimized Infrared LED and its use in an all-HgTe Nanocrystal-based active imaging setup, E. Bossavit et al, Adv opt Mater 10, 2101755 (2021)
Electroluminescence from HgTe Nanocrystals and its Use for Active Imaging, J. Qu et al, Nano Lett 20, 6185 (2020)
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)

Devices integration necessarily 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 alignment 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 (conducted on tempo and Antares 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.

Tempo beamline