Emmanuel Lhuillier

III–V nanocrystals (NCs) are emerging as a leading platform for short‐wave infrared sensing, yet a deeper understanding of their electronic structure is still needed. Paradoxically, although the corresponding bulk materials have been extensively studied, the evolution of optical properties at low temperatures (relevant to boost performances), and under pressure (likely induced by a shell introduced to prevent oxidation) has been scarcely investigated in NCs. We therefore conduct structural and spectroscopic studies to explore the (P;T) electronic phase diagram of InAs NCs with various sizes. Cooling induces a blue shift of the optical spectrum, thus reducing the spectral window. The temperature dependence shows an increase in dE/dT with the optical band gap, from which we derive an empirical law capable of predicting the temperature dependence for InAs NCs over a broad size range. Under pressure, we show that the zinc blende phase remains stable up to 12 GPa in nanocrystalline InAs, well above the pressure induced by a ZnSe shell. The pressure dependence of the band gap is found to be around 50 meV/GPa, with no significant size dependence. The 30‐band k.p model is used to quantify how the quantum confinement impacts the temperature and pressure dependence of the optical features.

Colloidal lead sulfide (PbS) nanocrystals (NCs) are emerging as cost-effective and solution-processable materials for infrared (IR) detection. Their use in a space environment is conditioned by their radiation tolerance. This study investigates the intrinsic robustness of PbS NC-based photoconductive devices to high-dose x-ray irradiation (up to 1.6 Grad [PbS]), far above the requirements for deep-space operation. PbS NC films exhibit gradual performance degradation without abrupt thresholds, attributed to their polycrystalline nature, which localizes defects and mitigates long-range lattice disruption. Optoelectronic measurements reveal a drop in both the dark and illuminated response, yet the signal-to-noise ratio improves due to the faster decay of the dark current. Spectroscopic analyses (x-ray photoemission spectroscopy/hard x-ray photoemission spectroscopy) confirm that the conductivity change can be attributed to x-ray-induced oxidation, which affects both Pb and S, forming sulfate and lead hydroxide phases that propagate throughout the NC volume. This oxidation reduces the effective NC size, blue-shifting the excitonic peak. Despite this, PbS NCs exhibit exceptional radiation hardness, comparable to that of radiation-hardened CMOS devices. These findings position PbS NCs as viable candidates for spaceborne IR detection, especially in oxygen-free environments where oxidation is naturally limited.

Achieving high‐performance optoelectronic devices based on two‐dimensional van der Waals (vdW) heterostructures relies critically on the precise control of interfacial properties, in particular the formation and modulation of Schottky barriers. However, direct operando imaging of the energy landscape at these interfaces, which is critical for rational device design, remains highly challenging. Here, we employ nanoscale scanning x‐ray photoemission microscopy to visualize the spatial distribution of electric fields and band alignment within a model 2H‐TaS ₂ (metal)/2H‐MoSe ₂ (semiconductor) vdW heterostructure under applied bias. By tracking core‐level binding energy shifts with 700 nm spatial resolution, we reveal the accumulation of electric fields at both 3D metal–2D semiconductor and 2D metal–2D semiconductor interfaces, indicative of a Schottky barrier whose height depends on the flake thickness. Bulk‐like MoSe ₂ exhibits negligible interfacial resistance, whereas a barrier (≈0.75 eV) emerges for the quantum‐confined form of the flake. These findings provide a direct visualization of charge injection pathways and underscore the role of quantum confinement in tuning barrier heights, offering a roadmap for engineering contacts in vdW‐based devices.

Monochromatic Al Kα (1486.6 eV) and monochromatic Cr Kα (5414.8 eV) radiation sources were used to acquire x-ray photoelectron spectroscopy (XPS) and hard x-ray photoelectron spectroscopy (HAXPES) data on bulk semimetallic HgTe. The reported spectra include survey scans, high-resolution core-level spectra of Hg and Te, and x-ray-excited Auger transitions. These data provide reference binding and kinetic energy values and are intended to support future XPS and HAXPES studies of HgTe and related materials.

Infrared (IR) sensing is essential for space applications such as remote sensing and spectroscopy, where sensors must withstand harsh radiation environments. Traditional IR sensors rely on II–VI and III–V semiconductor thin films, but emerging technologies like colloidal nanocrystals (NCs) offer cost-effective and scalable alternatives. However, the current study dedicated to their radiation tolerance remains very limited, thus leaving their potential unclear. This study investigates the radiation hardness of short-wave infrared (SWIR) photodiodes based on HgTe/CdS core–shell NCs, focusing on their resilience to X-ray, high-energy proton, and He+ ion irradiations, key challenges for space missions. The HgTe/CdS NCs, known for their thermal stability and low dark current, were processed into a diode stack and subjected to irradiation. Using X-ray photoemission spectroscopy (XPS) and depth profiling, we correlated optoelectronic degradation with nanoscale chemical and structural modifications, such as anion oxidation and cation redistribution. These findings highlight the potential of colloidal NCs to operate in a harsh radiation environment.

The demand for ultranarrow spectral emission below 10 nm is critical for next-generation displays. Although current colloidal nanocrystals are successful in light down-conversion applications, they fall short in matching the stringent color purity requirements set by standards like Rec. 2020. Achieving such narrow linewidths through material engineering alone remains elusive, necessitating innovative light management strategies that avoid optical losses and maintain device efficiency. Here, we present a novel 2D colloidal heterostructure design, combining a CdSe core nanoplatelet, a CdS crown, and a CdZnS shell, to achieve bright bicolor emission in the solid state (green/red) emission with tunable intensity ratios controlled by excitation power (either optical or electrical). Integration of these nanoplatelets into a dielectric cavity further narrows the emission linewidth to sub-2 nm while enhancing the photoluminescence intensity by up to 200 times, meeting the Rec. 2020 color purity targets. This approach paves the way for a strategy avoiding complex laser-based solutions.

Colloidal HgTe nanocrystals (NCs) offer a versatile, solution‐processable platform for infrared optoelectronics, yet their integration into high‐performance diodes has long been hindered by surface‐trap‐limited open‐circuit voltage ( V _OC ), high dark currents, and insufficient thermal robustness. Here, we demonstrate that ultrathin CdS shells grown around HgTe cores, combined with an optimized cation‐exchange protocol, enable unprecedented passivation of trap states while reducing species interdiffusion and simultaneously improving interfacial band alignment. Implemented in a diode architecture employing SnO ₂ electron‐transport layers and Ag‐doped CdTe hole‐selective contacts, these HgTe/CdS NCs yield a two orders of magnitude reduction in dark current and a V _OC of 420 mV; exceeding half the optical bandgap for the first time in HgTe‐based NC photodiodes. Operated at room temperature, the devices exhibit detectivities up to 1.5 × 10 ^{1 1} Jones and fast response times below 200 ns. Leveraging the reduced dark current and improved film homogeneity, we further integrate the photodiodes into a dielectric Bragg cavity to achieve ultranarrow detection linewidths down to 90 cm ⁻¹ at 1.55 µm. This diode design benefits from a strong field enhancement, while the device absorption limits the linewidth. Our results establish surface‐passivated HgTe NCs as a viable route toward compact, narrowband, and thermally stable infrared photodetectors.

After displays, short- and mid-wave infrared (IR) sensing is seen as the next frontier for optoelectronic applications of colloidal semiconductor nanocrystals (NCs). Considerable research efforts have focused on two material platforms: lead (Pb) and mercury (Hg) chalcogenides. Although impressive progresses have brought this technology to the development of focal plane arrays, the presence of heavy metals is often recognized as a critical barrier to broader commercial adoption. This challenge has generated a push toward new synthetic pathways enabling greener IR-active NC materials. However, in practice, each material platform tends to create parallel, independent fields, thus mitigating the benefits of already established developments. In this perspective, we discuss how the Pb/Hg-based IR sensor legacy can benefit the emergence of III-V and silver chalcogenide platforms by offering genuine and critical discussions about the limitation of each kind of material. Finally, we propose some development strategies for the emergence of next generation greener NC-based IR imagers.