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Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance, an unfavourable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. HgTe quantum wells close to the topological phase transition are a proven example of such gapped graphene-like materials. In this work we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by a magnetic field and gate voltage.Two-dimensional massive and massless Dirac fermions in HgTe/CdHgTe quantum wells yield terahertz Landau emission. The emission frequency is continuously tunable with magnetic field or carrier concentration, over the range from 0.5 to 3 THz.

Passivation of HgCdTe is known to be a key point in the making of high performance cooled infrared imagers. In this work, the electrical properties of the passivation layer of n-type mid-wave HgCdTe layers are investigated, using metal–insulator-semiconductor (MIS) structures. Several CdTe based passivation stacks are explored, deposited by two different techniques. Some stacks also include a graded bandgap zone between the semiconductor and the passivation layer. Capacitance versus voltage (CV) measurements are conducted on every sample, and the different passivation structures are then compared with regard to their electrical properties. CV measurements can be challenging to interpret in this type of material, thus additional experimental techniques and numerical simulation tools are often useful in supporting a given interpretation. Special attention is taken concerning doping values extracted from capacitance voltage curves, compared to other techniques such as the Hall Effect or secondary ion mass spectrometry (SIMS). An apparent over-doping is witnessed at the interface of some samples, which can be explained by a defective interface. It is shown that an additional annealing on these structures moves the interface closer to flat band conditions and reduces the amount of excess charge in the passivation layer and defects at the interface. Nevertheless, a Fermi level pinning phenomenon has been evidenced on some of the samples, even when an additional annealing was performed, highlighting the presence of a huge interface trap density on the band edges. In some cases, interface traps are identified and characterized accurately by the conductance method. Their density is found to be in the 1011 cm−2 eV−1 range. A strong dependence on photon flux is observed for some types of interface defects. Two-dimensional (2D) finite element simulation of MIS structures are developed in parallel to support the analysis of the measurements, with an emphasis on photon flux dependence and graded bandgap layer effect. Several models of the electronic affinity of HgCdTe versus compositions from literature are tested. One of them provides a good fit to measurements.

This short paper corresponds to the talk given as an invited speaker during the ITaMSA 2021 conference, Bogor (Indonesia). In this short paper, the reader can find the major concepts used for the modeling and simulation of agroecosystems. On the one hand, the concept of Multi-Agents Systems is presented with the main properties of these systems. On the second hand, the foundations and the characteristics of Cellular Automata are detailed. Designing a system with a set of agents allows the modeler to focus on the interactions between entities. This type of modeling is more natural than a classical mathematical approach at the population’s scale. Finally, a case study is presented. This case study is designed with a freely available tool developed at the University of Brest (France) based on a multi-agents engine with Cellular Automata facilities.

A high-quality CdZnTe single crystal has been imaged with micrometer resolution using monochromatic x-ray Bragg diffraction at the bending magnet (BM)-05 beamline of the European Synchrotron Radiation Facility. Since this material is used to produce substrates for the epitaxial growth of infrared sensitive HgCdTe photon detectors, imaging the defects is of strong interest to visualize their arrangement within the bulk. We show that large field-of-view rocking curve projection maps can be acquired in transmission geometry using samples as thick as 0.5 mm thanks to the Borrmann effect. Furthermore, section topography can be applied to provide information on the depth of the observed defects allowing for a complete 3D localization of lattice distortions. Examples of 1.5 mm × 1.5 mm full width at half-maximum maps are given to illustrate the spatial arrangement of dislocations in a number of samples cut with respect to different crystallographic planes in a particular CdZnTe ingot.

This paper presents recent developments at Commissariat à l’Energie atomique, Laboratoire d’Electronique et de Technologie de l’Information infrared laboratory on processing and characterization of p -on- n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in short-wave infrared (SWIR) spectral band for the astrophysics applications. These FPAs have been grown using both liquid phase epitaxy and molecular beam epitaxy on a lattice-matched CdZnTe substrate. This technology exhibits lower dark current and lower series resistance in comparison with n -on- p vacancy-doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in long-wave infrared and very-long-wave infrared spectral bands with cut-off wavelengths from 10 μm up to 17 μm at 78 K and is now evaluated for the SWIR range. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy and liquid phase epitaxy have been investigated. Electro-optical characterizations have been performed on individual photodiodes from test arrays, whereas dark current investigation has been performed with a fully functional readout integrated circuit dedicated to low flux operations.

Photoluminescence decay (PLD) measurements have been performed on mid-wave infrared (MWIR) Hg-vacancy p -doped HgCdTe samples at temperatures ranging from 85 K to 330 K. The doping level is p 0 = 6 × 10 15 cm - 3 at 80 K and the cut-off wavelength is λ c = 4.2 μ m at 300 K. The PLD signal has been fitted with a photo-injection level dependent model in order to estimate the contributions from the different recombination mechanisms to the total minority carrier lifetime. Shockley–Read–Hall centers lying in the bandgap at 25 meV from the conduction or the valence band has been found to limit the minority carrier lifetime from 85 to at least 200 K. The value of the Auger 1 lifetime coefficient is extracted from the first instants of signal decay for each temperature and reaches G eei n i - 3 = 5 × 10 - 26 cm 6 s - 1 at 85 K. The temperature evolution of the different contributions to the lifetime are in accordance with dark current density measurements in HgCdTe photodiodes.

We report the bulk growth of single-crystal CdZnTe and characterization of material associated with large-area wafers produced from the CdZnTe ingots. Our experimental vertical gradient freeze set-up enables accurate detection of the beginning and end of the crystallization step by careful monitoring of the thermal cycle. Single crystal, (111)-oriented ingots with a diameter of 80 mm were routinely obtained without grain boundary or twin. The size of the CdZnTe ingots was extended to 115 mm in diameter, enabling production of large-dimension substrates suitable for infrared focal-plane arrays with megapixel-resolution. Crystal quality was investigated by double-crystal x-ray rocking curve mapping and by chemical revelation of etch pits. Typical mean values for the rocking curve full width at half maximum were in the range 20–40 arcs. Evaluation of etch pit density on the (111)Te face furnished values in the low 10 4 /cm 2 .

Nitrogen, phosphorus, arsenic, and antimony ions were implanted in Hg 0.3 Cd 0.7 Te (MCT) layers under the same implantation conditions. An identical annealing process was then applied to these layers to eradicate implantation damage and to activate the impurities. Implantation damage was investigated by direct visualization, by use of bright-field scanning transmission electron microscopy (BF-STEM). Secondary-ion mass spectrometry was used to investigate impurity diffusion on annealing. The combination of these two techniques revealed the significant effect of structural implantation damage on the diffusion process. Annealed layers were then investigated by high-resolution STEM imaging and energy-dispersive x-ray spectroscopy in STEM (STEM-EDX). This approach enables direct visualization and, therefore, further description of arsenic and antimony-rich nanocrystals.

We present molecular beam epitaxy growth of tensile-strained HgTe/CdTe thin films for realization of three-dimensional (3D) topological insulator structures. The growth temperature is investigated by looking at crystal quality using high-resolution x-ray diffraction, being found to be much lower than the usual surface temperature for low-cadmium-fraction HgCdTe material. The strain status of HgTe is checked as a function of thickness, and the first indication of strain relaxation is found to appear for thickness well below the critical thickness expected for this system. Surface and interface morphology are also investigated, and well-defined interfaces as well as atomically flat surfaces are demonstrated. Finally, transmission electron microscopy is used to image the material structure of a HgCdTe/HgTe/HgCdTe stack suitable for electronic transport experiments.

We take advantage of the zinc distribution of (211)B CdZnTe substrates to probe the lattice-mismatch-induced stress in long-wave infrared HgCdTe layers grown by molecular beam epitaxy. High-resolution x-ray diffraction is used to accurately determine the strain-free lattice parameters of both CdZnTe and HgCdTe, together with the in-plane components of the stress tensor. By using several wafers, the stress evolution is derived over a broad range of lattice mismatch. In particular, stress relaxation is evidenced for mismatch greater than 0.02% and 0.04% for tensile and compressively strained HgCdTe, respectively. In-plane strain anisotropy, expected for the (211) orientation, is only evidenced for the compressive configuration. Strain relaxation is correlated with substrate curvature and rocking-curve peak broadening, providing indirect evidence for plastic relaxation.