Marco Paye

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.

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.

Colloidal nanomaterials are now a cost‐effective strategy for the design of infrared imagers. Their increased maturity brings them to the point where the evaluation of their potential for space and astronomy applications becomes relevant. The first step is to test their robustness against irradiation, since this process is responsible for the performance degradation of most imagers. In this study, we explore the potential of HgTe nanocrystals for short‐wave infrared sensing under X‐ray and He ⁺ ion irradiation. To first assess the degradation of the material itself, we test the evolution of a single‐pixel photoconductive device upon irradiation and observe that only marginal degradation occurs for doses relevant to space applications, and degradation only occurs at a very high threshold, making this colloidal semiconductor quite promising to operate in harsh radiation environments. Complementary spectroscopic studies reveal very different degradation mechanisms upon X‐ray (leading to oxidation) and He ⁺ ion (sintering particles). We tested the potential of this material in a focal plane array and observed degradation, though not preventing imaging, in a range of doses where no effect was observed for the simple photoconductive device. This suggests that the CMOS readout circuit might be the bottleneck regarding operation under radiation.

Mercury telluride (HgTe) nanocrystals (NCs) are promising materials for infrared photodetection due to their size-tunable band edges and compatibility with colloidal synthesis. While optical studies have established the temperature dependence of their relative bandgaps, the evolution of their absolute electronic spectrum with cooling remains poorly understood, despite its critical role in the device operation. In this work, we investigate in situ the temperature-induced absolute energy shift of HgTe NCs' electronic states with varying band edge energies, using X-ray photoemission spectroscopy. We observe a systematic and reversible rigid shift of core levels toward lower binding energies upon cooling, reaching approximately 80 meV per 100 K, four times larger than the corresponding optical band edge shift (≈20 meV). This behavior is consistent across different NC sizes, making the impact more dramatic for the narrower bandgap NCs. Such absolute energy shifts can significantly alter carrier densities and interfacial band alignments, potentially creating Schottky barriers and reducing extraction efficiency in photodiode architectures. Our findings highlight the necessity of accounting for temperature-induced absolute energy shifts in the design of next-generation HgTe NC-based infrared detectors.