This work presents the initial realization of a photosensitive mid-wave infrared (MWIR) nBn structure utilizing n-type HgCdTe with a superlattice barrier, achieving dark current levels comparable to the highest-performing HgCdTe-based photodiodes globally. The MWIR n-HgCdTe nB(SL)n heterostructure was designed and fabricated via molecular-beam epitaxy (MBE). Experimental investigations of its electrophysical and photoelectric properties were conducted to assess its performance metrics. The structure exhibited exceptionally low dark current values, on the order of picoamperes, at an operating temperature of 160 K. The dark current in the studied structure is compared with similar values presented by other authors, as well as with the benchmark Rule07 and Law19. A comparative analysis reveals that the fabricated photosensitive nBn MWIR structure, based on MBE-grown HgCdTe with a superlattice barrier layer, exhibits dark current density values comparable to the highest-performing global counterparts in the MWIR range. In the temperature range of 200–230 K it is possible to realize the values of dark current density close to the limit of background radiation noise.

In this work, we studied the persistent photoconductivity(PPC) spectra in single HgTe/CdHgTe quantum wells with different growth parameters and different types of dark conductivity. The studies were performed in a wide radiation quantum energy range of 0.62–3.1 eV both at T = 4.2 K and at T = 77 K. Common features of the PPC spectra for all structures were revealed, and their relation to the presence of a CdTe cap layer in all structures and the appropriate cadmium fraction in the CdHgTe barrier layers was shown. One of the features was associated with the presence of a deep level in the CdTe layer. In addition, the oscillatory behavior of the PPC spectra in the region from 0.8–1.1 eV to 1.2–1.5 eV was observed. It is associated with the cascade emission of longitudinal optical phonons in CdHgTe barrier.

Lasing from HgCdTe microdisc cavities is demonstrated at wavelengths as long as 22 — 25 μm. The optical threshold and operation temperature are far from being limited by intrinsic recombination processes. The employed ion etching technology appears to introduce additional defects in the vicinity of the microdiscs, degrading figures of merit as the height of the cavity increases. However, a watt-level mid-infrared pumping source should suffice for lasing in microdiscs with moderate height and ~100 μm diameter.

Spectral studies of the photoconductivity in the temperature range of T = 5–70 K, as well as studies of the magneto-absorption and magnetotransport at T = 4.2 K, have been performed in a HgTe/CdHgTe heterostructure with a double quantum well under an “optical gate” effect. Studies of magneto-absorption spectra under the controlled optical exposure have made it possible to observe absorption lines caused by both the cyclotron resonances of electrons and holes simultaneously. The coexistence of electrons and holes in the HgTe/CdHgTe double quantum well with a relatively large bandgap ( 80 meV) indicates the appearance of a strongly inhomogeneous light-induced distribution of charge carriers in the plane of the structure. Experimental results obtained clearly demonstrate disadvantages of the control of the Fermi level positions in heterostructures with HgTe/CdHgTe quantum wells by means of the optical gate.

The characteristics of a highly sensitive express bench for nonlinear optical diagnosis of crystalline structures such as sphalerite by generation of the second harmonica are presented. The analysis of the possibilities of quantitative and qualitative characterization of the features of the crystalline parameters of the layers of heteroepitaxial structures CdxHg1-xTe on substrates from GaAs with orientation (013) was carried out. The results were obtained by deviations of orientation in layers from the orientation of the substrate, which arose during the epitaxy, to determine the existence of stresses. The high sensitivity of the bench revealed the presence/absence of micro-particles with a disordered crystalline structure. Experimental results of reversible modification of the "in situ" crystalline state of CdxHg1-xTe structures with short-term local radiation exposure of high power laser radiation are given. New experimental data have been presented showing that the components of the nonlineaic susceptibility tensor chixyz(ω) of the crystalline structure of CdxHg1-xTe depend on composition and are an order of magnitude larger than similar components of tensor in CdTe and GaAs. Keywords: sphalerite crystals, second harmonica, azimuth angular dependence, tensor of nonlinear susceptibility, tensions, microparticle, radiation heating, heterostructures CdxHg1-xTe.

The subject of study is barrier nBn structures based on ( 013 ) Cd x Hg 1- x Te / CdTe / ZnTe / GaAs solid solutions. The purpose of the work is the creation of barrier nBn structures based on CdxHg1-xTe x Hg 1- x Te solid solutions with a given composition distribution profile and doping level intended for the manufacture of highly sensitive infrared photodetectors in the spectral range of 3-5 mu m operating at elevated temperatures. Method. The growth of barrier nBn HgCdTe structures is carried out by molecular beam epitaxy on (013)GaAs substrates with ZnTe and CdTe buffer layers and control of the thickness and composition of the layers in real time by a high-speed ellipsometric method. Doping of the layers during the growth process to the required level is carried out with indium from a Knudsen-type effusion source with precision control of its temperature (flow). The composition and thickness of the layers are determined during the growth process from in-situ measurements of ellipsometric parameters and transmission and reflectance spectra with sequential etching of the ex-situ layers. The concentration of the majority charge carriers in the grown structures is determined from Hall measurements by the Van Der Pauw method using layer-by-layer etching. Main results. Barrier nBn structures based on HgCdTe are obtained. The parameters of the composition and thickness of the layers are 0.3-0.35, 0.6-0.8, and 0.31-0.36 mole fractions and 3-4, 0.2-0.35, and 1-1.3 mu m for the absorbing, barrier, and contact layers, respectively. The concentration of the majority carriers is ( 0.6 - 3 ) x 1016, 16 , ( 0.6 - 3 ) x 1016, 16 , and ( 0.9 - 5 ) x 1017 17 cm-3 - 3 for the absorbing, barrier, and contact layers, respectively. A good correlation between the distribution profile of the composition and the doping level throughout the thickness of the grown structure, which is specified during the growth process with the results of subsequent post-growth measurements, is shown. Practical significance. The results of growing and characterizing the nBn structure obtained in this work are intended for the development of infrared photodetectors for the size, weight, and power (SWaP) technology, with high sensitivity in the spectral range of 3-5 mu m, various formats, and operating at elevated temperatures, for infrared optoelectronic and thermal imaging devices. (c) 2024 Optica Publishing Group

Materials with linear electronic dispersion often feature high carrier mobilities and unusually strong nonlinear optical interactions. In this work, we investigate the THz nonlinear dynamics of one such material, HgCdTe, with an electronic band dispersion heavily dependent on both temperature and stoichiometry. We show how the band gap, carrier concentration and band shape together determine the nonlinear response of the system. At low temperatures, carrier generation from Zener tunneling dominates the nonlinear response with a reduction in the overall transmission. At room temperature, quasi-ballistic electronic dynamics drive the largest observed nonlinear optical interactions, leading to a transmission increase. Our results demonstrate the sensitivity of these nonlinear optical properties of narrow-gap materials to small changes in the electronic dispersion and carrier concentration.

The subject of the study is the mechanical stresses in the surface layer of the (013)HgCdTe/CdTe/ZnTe/GaAs structure. The aims of the study are to experimentally test a new sensitive null reflection method to detect weak local birefringence and to determine the basic characteristics of residual mechanical stresses in local regions of the nearsurface graded wide gap HgCdTe layer in the (013)HgCdTe/CdTe/ZnTe/GaAs structure while analyzing the impact of crystalline perfection on the magnitude of these stresses. Method. The characteristics of the second harmonic signal of the laser IR radiation reflected from the surface of a rotating sample passed through a nonlinear crystal, which is exposed to synchronization for polarization perpendicular to the laser radiation, are registered. Main results. The new null reflection method, based on the excitation of second harmonic generation in a nonlinear LiIO3 crystal by reflected infrared laser radiation from a pulsed YAG:Nd laser at 1.064 mu m, is developed. This sensitive method allows us to get information on the anisotropy of the polarization of the reflected radiation due to residual deformation. The maxima of the second harmonic signals are accurately quantified. Observations of the fine structure in these maxima reveal a complex pattern of residual stresses linked to disoriented regions. Stress calculations in the near-surface region of the HgCdTe layer, which has a composition of x = 0.47, yield results of (-20.5 +/- 2) MPa. The magnitude of the SHG signal for layers with higher crystalline perfection is about 1.5 times smaller than for those with lower quality, corresponding to a force of 2.3 x 10-3 N. Practical significance. The findings have practical significance for measuring residual stresses in local areas of surface layers in various complex multilayer structures, both by area and depth, through layer-by-layer etching. This allows for the determination of how layer growth parameters during and after epitaxy influence emerging stresses and helps identify critical parameters of the technological process. (c) 2024 Optica Publishing Group

Room-temperature photoluminescence (PL) spectra of intensely pumped HgTe/CdHgTe quantum well (QW) heterostructures emitting at around 5 mu m wavelength have been investigated. Based on the model description of the PL spectra using a free-electron recombination band approach, effective electronic temperatures were determined depending on the excitation density. Within the quasi-steady-state approximation, we establish the balance between pump-induced heating of the electron gas in the QWs and phonon-mediated dissipation of this excess energy and deduce hot-phonon lifetime of similar to 0.47 ps. Maximum operating temperatures for optically pumped HgTe/CdHgTe QW laser heterostructures emitting at around 5 mu m are estimated depending on the excitation wavelength, and lasing at Peltier temperatures appears feasible for the pump wavelength of about 3 mu m. Thus, the entire 3 similar to 5 mu m atmospheric transparency window can be potentially covered by thermoelectrically cooled HgCdTe-based laser sources.

Subject of study. The application of superlattices as barrier layers in unipolar barrier nBn structures based on n-HgCdTe grown by molecular beam epitaxy is studied. Aim of study. . The aim is the analysis of the current state of theoretical and experimental research on the creation of unipolar photosensitive barrier nBn structures based on Hg1-xCdxTe 1- x Cd x Te grown by molecular beam epitaxy with superlattices as the barrier layer. Method. To achieve the aim, the results of theoretical and experimental studies of the use of superlattices as barrier layers in unipolar barrier nBn structures based on n-HgCdTe grown by molecular beam epitaxy were analyzed. Ab initio modeling of the energy diagram of superlattices in general and superlattices based on HgCdTe in particular is an extremely labor-intensive task. Therefore, the results of similar calculations performed by other authors, as well as the results of experimental studies that verify these calculations, were analyzed for the purpose of assessing the applicability of superlattices as the barrier in HgCdTe nBn structures. The goal was to determine the optimal values of the superlattice parameters based on this analysis. Main results. Based on the analysis of the results of currently known theoretical and experimental works that use superlattices as barriers in nBn structures based on n-HgCdTe, the ranges of optimal values of superlattice parameters (compositions and thicknesses of superlattice barrier layers and quantum wells) were determined. The need for additional research on the protection (passivation) of the side faces during the manufacture of experimental samples in the configuration of mesa structures to minimize the contribution of surface leakage currents to the dark current of the photosensitive structure was also noted. Practical significance. This work was aimed at analyzing the current state of the research in the area under consideration and determining which configurations of superlattice barriers seem to be optimal. As the use of superlattices in barrier nBn structures based on n-HgCdTe is considered to be the most promising way to eliminate the potential barrier for minority charge carriers, the results of this work can form the basis for developing the design of photosensitive structures in the MWIR and LWIR ranges and the subsequent creation of photodetector elements. (c) 2024 Optica Publishing Group

Amplified interband emission within the 14–24 μm range is investigated in HgCdTe-based quantum wells under optical pumping. Carrier lifetimes are shown to be marginally limited only by Shockley–Read–Hall recombination, fully realizing the advantage of relativistic energy spectra of 2D HgCdTe in terms of suppressing the Auger processes. By carefully optimizing the waveguides and mitigating carrier heating, we achieve amplification thresholds as low as 1.5–2 W/cm2 at a pulse duration of 20–500 μs. With last generation quantum cascade lasers used for optical pumping, we estimate that continuous-wave HgCdTe lasers can operate in the very long-wavelength range (15–30 μm) and beyond.

Various designs of dielectric waveguides made of heterostructures with CdHgTe quantum wells grown by molecular beam epitaxy have been studied to generate stimulated emission in the 15–30 μm wavelength range. The reduction of radiation losses in optimized structures has made it possible to reduce the threshold intensity of the generation of stimulated emission to ~100 W/cm 2 . Modernized growth technology has ensured the reduction of the residual cadmium content in HgCdTe quantum wells to 2.5%, which has allowed us to increase the threshold energy of Auger recombination, as well as the maximum temperature for the observation of stimulated emission at interband transitions above 100 K. The results obtained are prerequisites for the implementation of coherent radiation sources exceeding in characteristics of lead–tin chalcogenide lasers used in the 15–30 μm spectral range.

The arsenic impurity is widely considered to be the best choice for p -type doping of HgCdTe ternary alloys, which has been a formidable problem for decades. This work studies the terahertz photoconductivity of Hg 1– x Cd x Te with x ∼ 0.22 doped with arsenic and subjected to activation annealing to obtain p- type conductivity. In addition to the inevitable photoexcitation lines of mercury vacancies, which act as double acceptors, the spectra contain a distinctive line associated with the photoexcitation of the arsenic-related acceptor. In contrast to the predictions of the effective mass approximation, the binding energy of the acceptor is found to be about 25 meV. The possible reasons for this unexpectedly high chemical shift, which is not quite consistent with the data recently obtained from photoluminescence and Hall effect measurements, are discussed.

The studies of the interband electron transition energy in multiple Hg1-xCdxTe/Hg1-yCdyTe quantum wells (MQWs) at room temperature were carried out. The MQWs were grown on the (013) GaAs substrate by molecular beam epitaxy, with the layer composition and thickness being measured by the in-situ ellipsometric parameters measurement at the nanometer level. The Hg1-xCdxTe barrier composition and width were x = 0.69 and 30 nm, respectively. The Hg1-yCdyTe well composition was y = 0.06–0.10, and the width varied in the range of 2.7–13 nm. The experimental data of the interband electron transition energy were determined by the absorption spectral analysis. The calculation of the interband electron transition energy was carried out on the basis of the four-band Kane model. A good agreement between the experimental and calculated data was obtained. It was shown that MQWs may be used as a photosensitive material for creating infrared optoelectronic devices operating in different modes in the range of 3–10 μm at room temperature.

Due to their widely tunable bandgap, HgCdTe heterostructures with quantum wells are a promising material system for semiconductor lasers in the entire mid-infrared range. Recently, Auger-suppressed structures allowed interband stimulated emission (SE) in the atmospheric transparency window 3–5 μm well above 200 K, while previously it was limited to temperatures below 175 K. In contrast to earlier works focused on ridge or vertical emitting HgCdTe lasers, here we demonstrate a whispering gallery mode microdisk (d = 50 μm) laser operating under optical pumping at ∼4 μm in the temperature range attainable by the thermoelectric cooling. Above 200 K, the emission spectrum consists of multiple 0.37-meV-wide peaks associated with the modes of the disk resonator. Laser generation is achieved up to 230 K, which is 40 K lower than the quenching temperature of SE in the unprocessed macroscopic sample. We associate the difference with the optical losses introduced by the inclined walls of the disk.

A study of residual mechanical stresses in the surface layer of the HgCdTe/CdTe/ZnTe/GaAs structure based on the registration of the second harmonic signal characteristics of reflected IR laser radiation from the surface of the studied sample passed through a nonlinear crystal was carried out. It is shown that such a sensitive method makes it possible to obtain information about the anisotropy of the polarization of the reflected radiation, caused by the residual deformation. Observations of the fine structure of the angular sweep of the second harmonic signal suggest a complex structure of residual stresses related to the presence of misoriented areas. The results were compared with data obtained from measurements of the azimuthal dependence of the self-reflected second harmonic signal from the sample surface.

A large inhomogeneity of the minority lifetime from 1 to 10 μs at 77 K over the area is observed in some experiments when high-quality HgCdTe layers of the electronic type of conductivity are grown on GaAs substrates with a diameter of 76.2 mm with the (013) orientation by the method of molecular beam epitaxy. As a rule, the such lifetimes are determined by carrier recombination at Shockley-Hall-Read (SHR) centers. Modern studies and ideas about the nature of the SHR centers do not allow us to explain the observed results. The measurements of HgCdTe layers by the second harmonic generation showed the existence of a quasi-periodic change in the signal at the minima of the azimuthal dependence, which is associated with the appearance of misoriented microregions of the crystal structure. The amplitude of the quasi-periodic change in the signal decreases with increasing lifetime and completely disappears for regions with higher lifetime values. Similar dependences are observed during etching of HgCdTe layers, which indicates the existence of misoriented microregions in the bulk. Thus, misoriented microregions of the crystal structure have a significant effect on the lifetime and are new centers of Shockley-Hall-Read recombination. Keywords: HgCdTe layers, lifetime, second harmonic, azimuthal angular dependences, recombination centers, misoriented microregions.

Persistent photoconductivity (PPC) spectra of HgTe/CdHgTe heterostructures with double quantum wells with different cap layers have been studied in the radiation excitation range 0.62–3.1 eV. We have shown that the material of the cap layer defines key features of the PPC spectra—local extrema—and their origin. An unusual oscillatory behavior of the PPC spectra is demonstrated. Such a behavior is shown to be independent of both cap and barrier layers.

The PT -symmetric photoconductivity has been detected for the first time in microwave-irradiated heterostructures based on thick Hg 1 − x Cd x Te films with the CdTe content x corresponding to the topological phase although the magnetic field symmetry ( T symmetry) and the symmetry in the positions of potential contact pairs ( P symmetry) are not conserved separately. The microwave photoconductivity in similar heterostructures based on the trivial Hg 1 − x Cd x Te phase is both P - and T -symmetric.