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Among materials produced as colloidal quantum dots (CQDs), HgTe has a special status being the only material covering the whole infrared range from the visible to the THz (0.7–100 µm). This unique property resulting from its electronic structure, combined with an air stability and a capacity for charge conduction has generated consistent and massive efforts to produce and improve HgTe CQDs over the past two decades. Meanwhile, HgTe CQDs offer an infrared platform more advanced than any other colloidal alternatives in the mid‐wave infrared regarding their integration into advanced photonic and optoelectronic applications. Here, the latest developments of HgTe CQDs relative to the material's growth, electron structure modelling, its integration into photonic structures and its transfer as the active material from single element devices toward complex sensors and infrared imagers are reviewed. Finally, a discussion about the potential of this material for industry, rising new challenges beyond economical and production considerations at low technological readiness level, relative to the material and device design, is also included. [ABSTRACT FROM AUTHOR]

As they have gained maturity, colloidal nanocrystals (NCs) have also expand the spectral range over of which they could be used for photonic and optoelectronic applications. In particular, the infrared use of NCs has become of utmost interest to develop cost‐effective alternatives to current technologies. It is then critical not to let the material dictate the light–matter interaction, which is why the coupling of NCs to photonic cavities has been proposed. For infrared NCs, this approach has first been devoted to the control of absorption with in mind the increase of the signal magnitude for detectors. A Lot of efforts have been focused on the use of metallic metasurfaces. However, these generate significant optical losses and yield low quality factor. Here, this study rather focus on the coupling of infrared NCs to a dielectric mirror cavity. HgTe/CdS core‐shell NCs are used and integrated into a cavity made of aperiodic dielectric mirrors. The effect of the substrate is systematically study on spectral linewidth, carrier dynamic, and emission directivity. The cavity is shown to narrow the PL by a factor 10, while focusing the emission over a 12° angle. Monitoring the power dependence of the emission, this study shows that the cavity leads to 250 K increase in the effective electronic temperature. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are valuable for their potential applications in optoelectronic devices. However, they are susceptible to thermal degradation during processing and while in use. Mitigating thermally induced sintering, which leads to absorption spectrum broadening and undesirable changes to thin film electrical properties, is necessary for the reliable design and manufacture of CQD-based optoelectronics. Here, low-temperature metal–oxide atomic layer deposition (ALD) was investigated as a method for mitigating sintering while preserving the optoelectronic properties of mercury telluride (HgTe) CQD films. ALD-coated films are subjected to temperatures up to 160 °C for up to 5 h and alumina (Al2O3) is found to be most effective at preserving the optical properties, demonstrating the feasibility of metal–oxide in-filling to protect against sintering. HgTe CQD film electrical properties were investigated before and after alumina ALD in-filling, which was found to increase the p-type doping and hole mobility of the films. The magnitude of these effects depended on the conditions used to prepare the HgTe CQDs. With further investigation into the interaction effects of CQD and ALD process factors, these results may be used to guide the design of CQD–ALD materials for their practical integration into useful optoelectronic devices. [ABSTRACT FROM AUTHOR]

Highly responsive, low noise, and inexpensive photodetectors that operate in the mid‐infrared (MIR) wavelength regime are in high demand for applications ranging from fundamental science to large scale industries. However, simultaneously achieving all this in one device architecture is very challenging. In this work, mercury telluride (HgTe) colloidal quantum dot (cQD) based photodetectors are systematically improved by the introduction of new metamaterial designs. The new designs are found by utilizing simulations. Thereby the structures are optimized to increase the responsivity and simultaneously decrease the noise spectral current density. This is achieved by focusing on improving the photogenerated charge carrier collection efficiency while reducing the active material volume without altering the near unity absorption. A standard metamaterial perfect absorber architecture based on disc resonators is used as a starting point for the optimization process. By optimizing the carrier extraction through contact engineering, resulting in a narrow slot metamaterial, an overall ≈13‐fold responsivity and ≈345‐fold detectivity increase is achieved. The final metamaterial design reaches a responsivity of 16.2 A W−1 and detectivity of 6×108 Jones at a wavelength of 2710 nm. The analysis therefore provides a route to improve the responsivity and noise characteristics of mid‐infrared photodetectors based on cost‐efficient colloidal quantum dots. [ABSTRACT FROM AUTHOR]

Weak localization in a highly disordered quantum well CdxHg1 – xTe/HgTe/CdxHg1 – xTe with a thickness of d = 20 nm is experimentally investigated. An analysis is made of the anomalous positive magnetoresistance (APM) caused by the suppression of the interference correction to the conductivity by a magnetic field on both sides of the charge neutrality point: for a two-dimensional semimetal and for a two-dimensional electronic metal. For the same values of resistivity, the APM peak in a 2D semimetal has a much wider width than in a 2D electron gas. A quantitative comparison of the obtained results with the theory allows, in particular, to conclude that the intensity of carrier transitions between subsystems in the 2D semimetal binary system is maximum near the charge neutrality point, where the concentrations of electrons and holes are close, and decreases as the difference in concentrations increases. [ABSTRACT FROM AUTHOR]

HgTe nanocrystals offer a unique spectral tunability with both absorption and emission covering the near and mid‐infrared as well as the THz window. Nevertheless, a very limited amount of work is dedicated to electroluminescence from this material. An efficient diode not only requires designing a structure that achieves a high electrical efficiency (i.e., efficient electron and hole injections), but also finding a way to efficiently extract the emitted photons. The shift from visible to infrared certainly demands revisiting the strategies proposed for shorter wavelengths (microlens arrays). Here, a metallic grating is used to enhance the photoluminscence signal up to a factor of 4 while enabling directionality in the emission, which is driven by the grating period. [ABSTRACT FROM AUTHOR]

Due to the appeal of room temperature operation and low‐cost potential, colloidal quantum dots (CQDs) have become an alternative to traditional epitaxial materials for infrared photodetection. However, various device structure designs and different functional material layers are required to obtain high photodetection performances for different infrared subranges. In this work, a straightforward method is introduced for building CQD p‐i‐n homojunction as well as the inverted n‐i‐p homojunction photodetector, by preparing various doping type and density CQD inks with a mixed phase ligand exchange method. It is approved that both normal and inverted homojunctions show the specific detectivity D* as high as 1012‐1011 Jones and external quantum efficiency near 90% at high operating temperature. It is also approved that the method works for multiple infrared subranges such as 1.5 µm that covers the conventional wavelength for fiber‐optical communication (1530–1565 nm), 1.3–1.9 µm that is about the short‐wave infrared (SWIR), 1.3–2.5 µm that covers extend SWIR (beyond the standard InGaAs sensors, 1.75 µm), and 3.6 µm that belongs to mid‐wave infrared (MWIR). Applications such as spectrometer and infrared imager are also demonstrated. [ABSTRACT FROM AUTHOR]

Nanocrystals' (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm−2 and can be operated over a broad range of temperatures (130–300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W−1 or an external quantum efficiency of 500%) over a broadband spectral range. [ABSTRACT FROM AUTHOR]

Studying the optical performance of carbon nanotubes (CNTs) filled with guest materials can reveal the fundamental photochemical nature of ultrathin one-dimensional (1D) nanosystems, which are attractive for applications including photocatalysis. Here, we report comprehensive spectroscopic studies of how infiltrated HgTe nanowires (NWs) alter the optical properties of small-diameter (dt < 1 nm) single-walled carbon nanotubes (SWCNTs) in different environments: isolated in solution, suspended in a gelatin matrix, and heavily bundled in network-like thin films. Temperature-dependent Raman and photoluminescence measurements revealed that the HgTe NW filling can alter the stiffness of SWCNTs and therefore modify their vibrational and optical modes. Results from optical absorption and X-ray photoelectron spectroscopy demonstrated that the semiconducting HgTe NWs did not provide substantial charge transfer to or from the SWCNTs. Transient absorption spectroscopy further highlighted that the filling-induced nanotube distortion can alter the temporal evolution of excitons and their transient spectra. In contrast to previous studies on functionalized CNTs, where electronic or chemical doping often drove changes to the optical spectra, we highlight structural distortion as playing an important role. [ABSTRACT FROM AUTHOR]

The goals of this study are to use density functional theory to study the core structure energetics of the 30° and 90° partial dislocations in HgTe, CdTe, and Hg0.7Cd0.3Te as well as the density of states of these dislocations in CdTe and Hg0.7Cd0.3Te. For the 30° partial dislocations, two stable dislocation pairs were found. The pair with a double‐periodic α‐core (Te) dislocation and a single‐periodic β‐core (Hg/Cd) dislocation was found to be the most stable out of the two for the simulation sizes tested. For the 90° partial dislocations, two stable dislocation pairs were also found. The first has a single‐periodic β‐core dislocation and a single‐periodic α‐core dislocation, whereas the second has a double‐periodic β‐core dislocation and a single‐periodic α‐core dislocation. The most stable out of the two depends on the simulation size tested. For both of these partial dislocations in Hg0.7Cd0.3Te, it was found that it is energetically favourable for Hg atoms to segregate to the dislocation cores. Furthermore, in CdTe and Hg0.7Cd0.3Te, it was found that the 90° partial dislocations are likely to be more detrimental to the material optoelectronic properties since they introduce more mid‐gap states within the band gap in comparison to the 30° partial dislocations. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires (NWs) are believed to play a crucial role for future applications in electronics, spintronics and quantum technologies. A potential candidate is HgTe but its sensitivity to nanofabrication processes restrain its development. A way to circumvent this obstacle is the selective area growth technique. Here, in-plane HgTe nanostructures are grown thanks to selective area molecular beam epitaxy on a semi-insulating CdTe substrate covered with a patterned SiO 2 mask. The shape of these nanostructures is defined by the in-plane orientation of the mask aperture along the <110>, <11¯0>, or <100> direction, the deposited thickness, and the growth temperature (GT). Several micron long in-plane NWs can be achieved as well as more complex nanostructures such as networks, diamond structures or rings. A good selectivity is achieved with very little parasitic growth on the mask even for a GT as low as 140 °C and growth rate up to 0.5 monolayer per second. For <110> oriented NWs, the center of the nanostructure exhibits a trapezoidal shape with {111}B facets and two grains on the sides, while <11¯0> oriented NWs show {111}A facets with adatoms accumulation on the sides of the top surface. Transmission electron microscopy observations reveal a continuous epitaxial relation between the CdTe substrate and the HgTe NW. Measurements of the resistance with four-point scanning tunneling microscopy indicates a good electrical homogeneity along the main NW axis and a thermally activated transport. This growth method paves the way toward the fabrication of complex HgTe-based nanostructures for electronic transport measurements., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Thanks to their narrow band gap nature and fairly high carrier mobility, HgTe nanocrystals (NCs) are of utmost interest for optoelectronics beyond the telecom window (λ > 1.55 μm). In particular, they offer an interesting cost-effective alternative to the well-developed InGaAs technology. However, in contrast to PbS, far less work has been dedicated to the integration of this material in photodiodes. In the short-wave infrared region, HgTe NCs have a more p-type character than in the mid-wave infrared region, thus promoting the development of new electron transport layers with an optimized band alignment. As for perovskites, HgTe NCs present a fairly deep band gap with respect to vacuum. Thus, we were motivated by the strategy developed for perovskite solar cells, for which SnO2 has led to the best performing devices. Here, we explore the following stack made of SnO2/HgTe/Ag2Te, in which the SnO2 and Ag2Te layers behave as electron and hole extractors, respectively. Using X-ray photoemission, we show that SnO2 presents a nearly optimal band alignment with HgTe to efficiently filter the hole dark current while letting the photoelectrons flow. The obtained I–V curve exhibits an increased rectifying behavior, and the diode stack presents a high internal efficiency for the diode (above 60%) and an external quantum efficiency that is mostly limited by the absorption magnitude. Furthermore, we tackle a crucial challenge for the transfer of such a diode onto readout circuits, which prevents back-side illumination. We also demonstrate that the diode stack is reversible with a partially transparent conducting electrode on the top, while preserving the device's responsivity. Finally, we show that such a SnO2 layer is also beneficial for electron injection and leads to an enhanced electroluminescence signal as the diode is operated under forward bias. This work is an essential step toward the design of a focal plane array with a HgTe NC-based photodiode. [ABSTRACT FROM AUTHOR]

Nanocrystals’ (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm−2 and can be operated over a broad range of temperatures (130–300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W−1 or an external quantum efficiency of 500%) over a broadband spectral range.

In quantum wells (QWs) formed in HgCdTe/CdHgTe heterosystems with a variable composition of Cd(Hg), Shubnikov-de-Haas (SdH) oscillations are investigated to characterize the Rashba-type spin-orbit coupling in QWs with both a normal and inverted band structure. Several methods of extracting the Rashba spin-splitting at zero magnetic field and their magnetic field dependences from the beatings of SdH oscillations are used for greater reliability. The large and similar Rashba splitting (25–27 meV) is found for different kinds of spectrum, explained by a significant fraction of the p-type wave functions, in both the E1 subband of the sample with a normal spectrum and the H1 subband for the sample with an inverted one. [ABSTRACT FROM AUTHOR]

The potential detectivity limits of HgTe nanocrystal quantum dot photodetectors are examined using a microscopic detailed balance model of carrier generation and recombination. We find that even with the fast nonradiative recombination typical of present materials, HgTe quantum dot solids can support equilibrium detectivities which are close to those of Auger-limited HgCdTe crystals. It is further shown that if such nonradiative recombination can be reduced so that Auger-limited performance is achieved, the confluence of fast radiative and slow Auger recombination should enable large upper limits on achievable detectivities when compared to HgCdTe. These results are discussed in the context of future advances in infrared photodetection with nanocrystal quantum dots. [ABSTRACT FROM AUTHOR]

Nanocrystals (NCs) have reached a high level of maturity, enabling their integration into optoelectronic devices. The next challenge is the combination of several types of devices into one complex system to achieve better on‐chip integration. Here, an all‐HgTe‐NC active imaging setup operating in the short‐wave infrared (IR) is focused on. First, the design of an optimized IR light‐emitting diode (LED) is focused on. It is shown that a halide technology processing enables an increase of the electroluminescence signal by a factor of 3, while preserving a low turn‐on voltage and a high brightness (3 W sr−1 m−2). Then the degradation mechanism of this LED under continuous operation is unveiled and a shift from band edge to trap emission is shown. This degradation process can be strongly reduced thanks to the encapsulation and the thermal control of the LED. Lastly, the IR emission of the LED is imaged using a focal plane array whose active layer is also made of HgTe NCs, paving the way for all‐NC‐based active imaging setups. [ABSTRACT FROM AUTHOR]

I am probably one of the few who remember the first Jaszowiec Conferences that took place in the Teacher's House. Memories of those old times are very blurred. However, I remember this period as full of enthusiasm and commitment to the study of new phenomena in the so-called "narrow energy gap" semiconductors. I also remember Professor Leonard Sosnowski, who was the highest authority for us, and who instilled in us the belief that "Physics is the Most Important" and should primarily regulate relations in our community. During these 50 years, since Professors Witold Giriat, Wiesław Wardzynski, and Józef Zmija took their first steps in the organization of "Jaszowiec", a local Polish meeting turned into a prestigious international conference, building the coherence of the entire Polish semiconductor physics community. When I consider what enabled the systematic development and great success of "Jaszowiec", what I see first is Sosnowski's principle that Physics is our common good which we should preserve. The key role of this principle is in line with the hundred-year tradition of "Hoza 69", born in II Rzeczpospolita. Despite turbulent times, this tradition has survived and is still alive among us. [ABSTRACT FROM AUTHOR]

The limited investigation of the optical properties of HgTe nanocrystal (NC) thin films has become a bottleneck for the electromagnetic design of devices. Using broadband ellipsometry, the refractive index (n) and the extinction coefficient (k) are determined for a series of HgTe NC films relevant to infrared sensing applications. Electromagnetic simulations reveal that the n value of HgTe NC thin films can conveniently be approximated by its mean spectral value n = 2.35 ± 0.15. This complex optical index is then used to design a diode with i) a reduced amount of Hg containing material (thin film < 150 nm) and ii) a thickness of the device better‐matched with the carrier diffusion length. It is demonstrated that introducing an aluminum grating onto the transparent conductive electrode leads to an enhanced absorption while reinforcing the work‐function difference between the two electrodes. Broadband (≈1 µm), non‐polarized, and strong absorption up to 100% is designed. This leads to a responsivity of 0.2 A W−1 and a detectivity of 2 × 1010 Jones for 2 µm cut‐off wavelength at room‐temperature, while the time response is as short as 110 ns. [ABSTRACT FROM AUTHOR]

In quantum wells (QWs) formed in HgCdTe/CdHgTe heterosystems with a variable composition of Cd(Hg), Shubnikov-de-Haas (SdH) oscillations are investigated to characterize the Rashba-type spin-orbit coupling in QWs with both a normal and inverted band structure. Several methods of extracting the Rashba spin-splitting at zero magnetic field and their magnetic field dependences from the beatings of SdH oscillations are used for greater reliability. The large and similar Rashba splitting (25–27 meV) is found for different kinds of spectrum, explained by a significant fraction of the p-type wave functions, in both the E1 subband of the sample with a normal spectrum and the H1 subband for the sample with an inverted one.

HgTe colloidal quantum dots (CQDs) are one of few materials that can realize near-to-midwave infrared photodetection. And the quality of HgTe CQD directly affects the performance of photodetection. In this work, we optimize the method of synthesizing HgTe CQDs to reduce the defect concentration, therefore improving the photoelectric properties. The photodetector based on HeTe CQD can respond to the light from the visible to mid-infrared band. Notably, a photoresponse to 4000 nm light at room temperature is realized. The responsivity and detectivity are 90.6 mA W -1 and 6.9 × 10 7 Jones under 1550 nm light illumination, which are better than these of most reported HgTe CQD photodetectors. The response speed reaches a magnitude of microseconds with a rising time of τ r = 1.9 μs and a falling time of τ f = 1.5 μs at 10 kHz under 1550 nm light illumination.

Transferring nanocrystals (NCs) from the laboratory environment toward practical applications has raised new challenges. HgTe appears as the most spectrally tunable infrared colloidal platform. Its low-temperature synthesis reduces the growth energy cost yet also favors sintering. Once coupled to a read-out circuit, the Joule effect aggregates the particles, leading to a poorly defined optical edge and large dark current. Here, we demonstrate that CdS shells bring the expected thermal stability (no redshift upon annealing, reduced tendency to form amalgams, and preservation of photoconduction after an atomic layer deposition process). The electronic structure of these confined particles is unveiled using k.p self-consistent simulations showing a significant exciton binding energy of ∼200 meV. After shelling, the material displays a p - type behavior that favors the generation of photoconductive gain. The latter is then used to increase the external quantum efficiency of an infrared imager, which now reaches 40% while presenting long-term stability.

The dynamical screening function of two-dimensional electron gas in a wide HgTe quantum well (QW) has been numerically modeled in this work. Calculations were performed in the Random Phase Approximation (RPA) framework and were based on the Lindhard equation. Our simulations directly incorporated non-parabolicity of bulk 2D carriers’ spectrum, which was obtained by full 8-band k.p method. Known from literature are the data that transport properties of HgTe QWs can be explained by graphene-like screening. We carried out the comparison of the screening function for the Schrödinger fermions in the inverted bands HgTe QW with the appropriate screening function for graphene monolayer with the Dirac fermions. In addition, the dependences of HgTe-specific screening function on temperature, scattering wave-vector and frequency have been studied with the purpose to ascertain the transport properties under high frequency radiation for the QW structures to be used as THz detectors. Plasmon frequencies of 2DEG in HgTe quantum well under study were calculated in the long-wave limit for T = 77 K.

• A plasmon-enhanced HgTe CQD photodetector with Ag NPs embedded. • Thickness optimization on short wave infrared photodetector. • Fast response speed with near-field enhancement. Surface plasmon resonances based on metal nanoparticles (MNPs) can intensively enhance the electric field strength and capture light in the near-field region, thus greatly improving the performance of photodetectors. Here, we investigate plasmon-enhanced HgTe colloidal quantum dot (CQD) short-wave infrared (SWIR) photodetectors with Ag NPs embedded. Thanks to Ag NPs' ability to trap the incident light, the light-to-dark current ratio of our enhanced CQD photodetectors with 10 nm Ag NPs is significantly increased by a factor of 5.7. Accordingly, the specific detectivity and responsivity are also enhanced, achieving about 8.92 × 1010 Jones and above 2 AW−1 under 2 V bias, respectively. [ABSTRACT FROM AUTHOR]

The continuum elasticity model is applied to investigate quantitatively the growth features and nucleation mechanism of quantum dots, nanopits, and joint QD-nanopits structures in CdZnHgTe quasyternary material system. We have shown that for the CdZnHgTe solid solution deposited on the CdTe substrate, the sign of the critical energy and volume of island is changed at the critical strain of ɛ* = 0.006 and ɛ* = 0.009 (ɛ = Δa/a), It is assumed that the mechanism of the nucleation is changed from the growth of quantum dots to the nucleation of nanopits at ɛ = ɛ*. Obviously, at the small mismatch (ɛ < ɛ*) the bulk nucleation mechanism dominates. However, at ɛ > ɛ*, when the energy barrier becomes negative and a large mismatch provides a low-barrier path for the formation of dislocations, the nucleation of pits becomes preferable energetically. [ABSTRACT FROM AUTHOR]

The dynamical screening function of two-dimensional electron gas in a wide HgTe quantum well (QW) has been numerically modeled in this work. Calculations were performed in the Random Phase Approximation (RPA) framework and were based on the Lindhard equation. Our simulations directly incorporated non-parabolicity of bulk 2D carriers' spectrum, which was obtained by full 8-band k.p method. Known from literature are the data that transport properties of HgTe QWs can be explained by graphene-like screening. We carried out the comparison of the screening function for the Schrödinger fermions in the inverted bands HgTe QW with the appropriate screening function for graphene monolayer with the Dirac fermions. In addition, the dependences of HgTespecific screening function on temperature, scattering wave-vector and frequency have been studied with the purpose to ascertain the transport properties under high frequency radiation for the QW structures to be used as THz detectors. Plasmon frequencies of 2DEG in HgTe quantum well under study were calculated in the long-wave limit for T = 77 K. [ABSTRACT FROM AUTHOR]

Mercury telluride colloidal quantum dots (CQD) hold potential for the fabrication of IR devices that operate in the range of near IR, through short-, mid-, and long wavelength (NIR, SWIR, MWIR, and LWIR, respectively). We synthesized a variety of colloidal HgTe QDs using the wet technique in a non-coordinating environment. Both a standard synthesis technique (mixing Hg and Te precursors and letting the nanocrystals grow and develop) and a more complex technique involving the controlled intermittent addition of precursors were applied. CQDs with sizes up to 20-30 nm were grown, although materials with sizes well above 10 nm did not show a distinct excitonic absorption peak. Our synthesized CQDs were used to fabricate photoconductive devices and measure their photoresponse. We present the synthesis techniques used in this work, photoconductive device fabrication and characterization. Devices with quantum efficiency of about 12.5% at a 4 V bias were obtained. [ABSTRACT FROM AUTHOR]

Over the past few years, colloidal nanoparticles have started to be investigated for their optical properties in the mid-infrared, past 3 μm. Research on detector application has led to background limited detection and fast video imaging at 5 μm. With further development, one could imagine that these new materials could vastly reduce the costs of infrared technology and this would lead to a trove of new applications for infrared imaging into our daily lives. This paper reviews the progress regarding the optical, transport, and photodetection properties of thin film based on these materials, and the three different ways by which infrared resonances have been realized with colloidal nanoparticles: interband absorption with small gap semiconductor quantum dots, intraband absorption in lightly doped quantum dots, and plasmonic resonances in heavily doped nanocrystals. [ABSTRACT FROM PUBLISHER]

We investigate the electronic and transport properties of HgTe 2D colloidal quantum wells. We demonstrate that the material can be made p- or n-type depending on the capping ligands. In addition to the control of majority carrier type, the surface chemistry also strongly affects the photoconductivity of the material. These transport measurements are correlated with the electronic structure determined by high resolution X-ray photoemission. We attribute the change of majority carriers to the strong hybridization of an n-doped HgS layer resulting from capping the HgTe nanoplatelets by S2– ions. We further investigate the gate and temperature dependence of the photoresponse and its dynamics. We show that the photocurrent rise and fall times can be tuned from 100 μs to 1 ms using the gate bias. Finally, we use time-resolved photoemission spectroscopy as a probe of the transport relaxation to determine if the observed dynamics are limited by a fundamental process such as trapping. These pump probe surface photovoltage measurements show an even faster relaxation in the 100–500 ns range, which suggests that the current performances are rather limited by geometrical factors. [ABSTRACT FROM AUTHOR]