The results of a study of photoluminescence (PL) of epitaxial films of Hg0.3Cd0.7Te and Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy are presented. A comparison of PL data with the results of optical transmission measurements and structural and microscopic studies showed that in terms of the degree of disorder of the solid solution, the studied Hg0.7Cd0.3Te films are not inferior in quality to the material synthesized by other methods. For Hg0.3Cd0.7Te films, PL data revealed significant composition fluctuations and the presence of acceptor states, which indicates the need to optimize the technology.

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

Subject of study. Epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and doped with arsenic to obtain hole-type conductivity in order to form p-n junctions for the production of infrared photodetector structures are studied. Aim of study. The types and characteristics of defects formed during arsenic doping of epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and the effect of doping on the level of disorder in the solid solution are determined. Method. Ellipsometry, optical transmittance, photoluminescence, and photoreflectance are used. Main results. The initial material is shown to have high quality in terms of film bulk and surface quality, and the quality was found to improve after two-stage activation thermal annealing. Annealing has been shown to activate the arsenic with the formation of shallow (7-8 meV) acceptor levels. No side defects were found to occur as a result of the introduction of arsenic into the films during growth and annealing. Practicalsignificance. This research demonstrated the effectiveness of doping epitaxial films of Hg0.7Cd0.3Te solid solutions with arsenic as an acceptor impurity in order to produce layers with hole conductivity during the production of photodiode structures. (c) 2024 Optica Publishing Group

The subject of the study is epitaxial films of Hg1-x 1 - x CdxTe x Te solid solutions with the mole fraction of CdTe, x , varying from 0.3 to 0.7, grown by molecular beam epitaxy, and intended for the manufacture of photodetecting and laser structures operating in the infrared range. The aim of the study is to determine the relationship between the optical and microscopic properties of Hg1-xCdxTe 1 - x Cd x Te solid solutions with fluctuations in their composition. The methods include optical transmission, photoluminescence, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Main results. By comparing the results of optical, structural, and microscopic studies, it is shown that, for the films with x : 0.3, the research data on optical properties make it possible to adequately estimate the bandgap and determine the chemical composition of the material. The high perfection of this material is shown, and it is confirmed that its disorder is caused only by the specifics of the formation of semiconductor solid solutions. For the films with x : 0.7, it is established that data on the bandgap and composition can only be obtained from ellipsometric studies and measurements of optical transmission, whereas photoluminescence spectra at temperatures up to room temperature are formed by optical transitions involving carriers localized on large-scale composition fluctuations. In the films with x : 0.7, the presence of uncontrolled acceptor states is also detected, which may indicate the need to optimize the technology of this material. Practical significance. The limits of applicability of photoluminescence studies for characterizing the properties of solid solutions are identified. The need for further optimization of the technology of materials with large (x x : 0.7) compositions is shown. (c) 2024 Optica Publishing Group

The 15-μm-pitch 640×512 FPA detectors with a long-wavelength sensitivity limit of 5.1 μm based on MCT layers grown by molecular-beam epitaxy on Si substrates were designed and fabricated. Both electrical circuit and topology of a 15-μm-pitch 640×512 ROIC for such FPAs were developed, according to which multiplexers ensuring operation of manufactured FPAs at a clock frequency of up to 20 MHz were fabricated. Using the flip-chip method on In bumps, hybrid 640×512 MCT-based FPA detectors with 15-μm pixel pitch were obtained. The best fabricated FPA detectors were found to have the following characteristics: mean NETD value < 18 mK and number of non-defective pixels > 99.8%.

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.

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.

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.

The results of a study of the optical and structural properties of wide-bandgap (x~0.7) layers in laser heterostructures based on Cd x Hg 1-x Te solid solutions grown by molecular beam epitaxy on (013)GaAs substrates, as well as epitaxial films similar to these layers in chemical composition, are presented. It is shown that the position of the maximum of the photoluminescence spectrum and the nature of its temperature shift are related to the disordering of the composition of the solid solution. Shallow and deep acceptor levels were found in the bandgap. The possible influence of disordering and acceptor levels in laser structures on the energy spectrum of carriers is discussed. Keywords: CdHgTe, laser structures, photoluminescence, defects, structural properties.

The energy structure of the size quantization levels in multiple Hg0.3Cd0.7Te/HgTe quantum wells grown via molecular beam epitaxy on a (013)GaAs substrate has been studied. Experimental and calculated energy positions of three size quantization levels are obtained.

The results of a study of the optical and structural properties of wide-bandgap (x~0.7) layers in laser heterostructures based on CdxHg1-xTe solid solutions grown by molecular beam epitaxy on (013)GaAs substrates, as well as epitaxial films similar to these layers in chemical composition, are presented. It is shown that the position of the maximum of the photoluminescence spectrum and the nature of its temperature shift are related to the disordering of the composition of the solid solution. Shallow and deep acceptor levels were found in the bandgap. The possible influence of disordering and acceptor levels in laser structures on the energy spectrum of carriers is discussed.

In this work, we study stimulated emission (SE) at 3–4 μm wavelengths from optically pumped bulk HgCdTe and HgTe/CdHgTe quantum-well heterostructures. It is proposed that, under intense excitation of such structures, energy relaxation of hot electrons occurs mostly via electron–hole scattering, while the relaxation of hot holes is direct, phonon-mediated. By balancing carrier generation/recombination and heating/cooling processes, we outline heat-induced limits to the operating temperatures of mid-IR HgCdTe lasers. Based on the existing experimental results for the SE around 3.5 μm, we predict that lasing at this wavelength may be achieved in 2.5 μm-pumped optical converters at temperatures as high as Tmax ∼ 270 K.

The results of comparative studies of the optical and structural properties of Hg0.7Cd0.3Te bulk crystals and epitaxial films grown by various methods are presented. The data of photoluminescence studies performed in the temperature range 4.2–300 K showed the similarity of the optical properties of different samples and indicated a significant disordering of the solid solution. According to X-ray diffraction data, however, the scale of the disordering was not directly related to the structural quality of the material. The prospects for using the material grown by various methods in optoelectronics applications are discussed.

Despite the ultimate performance of the existing cascade lasers, simple interband emitters in the mid-infrared (IR) can still be of interest as a cheaper and widely tunable alternative for some applications. In this work, we show mid-infrared stimulated emission (SE) at 5–6 μm wavelength from an optically pumped mercury–cadmium–telluride quantum well (QW) heterostructures at temperatures up to 200 K. At lower temperatures, the SE threshold appears to be mostly determined by conventional eeh Auger recombination, while the contribution of alternative QW-specific ehh Auger processes is limited. At higher temperatures, we establish heating of the electron gas by pumping radiation as a primary factor responsible for the thermal quenching of the SE. Consequently, both pumping scheme and QW designs should be carefully revised to minimize carrier heating in order to realize near-to-mid-IR optical converters operating close to ambient temperature. We suggest using low-barrier QWs to minimize excessive heat introduced in the QW upon carrier capture and also to eliminate eeh Auger processes involving excited QW subbands. Thus, mid-infrared HgCdTe lasers are expected to reach operating temperatures readily attainable under thermoelectric cooling.

A parametric model describing the spectra of optical constants n(λ) and k(λ) of a Hg1 – xCdxTe (MCT) solid solution for the x values in the range from 0.2 to 0.4 is developed. This model is based on empirical data measured in situ during the epitaxial growth of solid-solution layers. Several versions of application of the obtained model for in situ real-time determination of the MCT composition have been considered. A technique for determining the composition using spectral ellipsometric measurements is proposed, which ensures the error of no more than δx = ±0.0035.

The results of comparative studies of the optical and structural properties of Hg0.7Cd0.3Te bulk crystals and epitaxial films grown by various methods are presented. The data of photoluminescence studies performed in the temperature range 4.2−300K showed the similarity of the optical properties of different samples and indicated a significant disordering of the solid solution. According to X-ray diffraction data, however, the scale of the disordering was not directly related to the structural quality of the material. The prospects for using the material grown by various methods in optoelectronics applications are discussed.

We provide a review of the current state, problems and their solutions, and potential possibilities to develop the technology of the Molecular Beam epitaxy (MBE) to obtain CdHgTe structures on various substrates for infrared detectors. We present the data about MBE supervacuum units control tools for growth processes, collected according to used substrates preparation processes for substrate surfaces, growth of buffer layers on alternating substrates, and growth and alloying of CdHgTe layers. We present main defects of structures (such as line defects and macrodefects) and their least achieved concentration levels limiting the quality of detectors. We consider the data about problems of the external alloying of CdHgTe layers by dopants and the obtained electrophysical parameters of such layers. We provide photoelectric parameters of IR-detectors, close to theoretical ones and showing that the MBE technology is ready to produce CdHgTe/Si structures on six-inch diameters. We demonstrate results of the research and development of the growth and alloying of CdHgTe structures on GaAs substrates and Si substrates of 76.2-mm diameters, implemented at the Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences.

Optical transmission, photoluminescence and photoconductivity were used to study Hg 1− x Cd x Te with x = 0.7–0.8 (bandgap 0.8–1.1 eV at 300 K) grown by molecular-beam epitaxy. The studied material, which included layers used as spacers and barriers in potential- and quantum-well structures, showed a considerable degree of alloy disorder similar to narrower-bandgap HgCdTe grown by the same method. The observed disorder seemed to have no effect on the structural properties of the material and its optical absorption. Optimization of the growth technology of wider-bandgap HgCdTe should help improve the quality of potential- and quantum-well structures based on this material.