Over a wide temperature range, a study was carried out of the mechanisms of formation of dark current and photocurrent in an nBn structure based on n-HgCdTe, grown by molecular beam epitaxy, with a superlattice in the barrier region. The influence of different levels of constant illumination on the electrical characteristics of structures was studied. The behavior of the bulk current component JB and the surface leakage current component JS was analyzed at various bias voltages and temperatures. The study showed a strong dependence of dark current density on temperature. A significant effect of constant illumination with an IR LED on the current density value has been demonstrated. The dominance of current components JB over JS is shown throughout the entire range of bias voltages and temperatures studied.

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.

The results of the study of the MWIR photosensitive nBn structure based on HgCdTe with a superlattice in the barrier region in the dark mode of operation and under IR radiation are presented. An experimental nBn structure with mesa structures of different diameters based on epitaxial layers of n-HgCdTe with a barrier layer in the form of a superlattice was manufactured. Due to the use of a superlattice in the studied structure it was possible to reduce the barrier for minority charge carriers compared to a similar structure with a uniform barrier at the same bias voltage. A twofold reduction in the energy barrier for minority carriers is also shown for the bias voltage corresponding to the maximum photocurrent/dark current ratio. It is shown that it was possible to implement diffusion limitation of dark current at negative bias voltages on a mesa structure with a diameter of 0.1 mm. The studied mesa structures with a diameter of 0.1 mm demonstrated acceptable values of the dark current density, as well as photocurrents exceeding the dark current level by one order of magnitude at a certain bias voltage and temperature. The obtained values of the dark current density are several orders of magnitude lower than for any known MWIR nBn structures based on HgCdTe with a superlattice in the barrier region.

Subject of study. The work studied the formation of germanium quantum dots on silicon with (100) crystallographic orientation under different growth regimes. Aim of study. The work is devoted to conducting experimental studies of the influence of growth mechanisms on the formation of germanium layers and quantum dots on a silicon (100) substrate for the production of optical elements based on silicon-germanium nanostructures. Methods. After pre-epitaxial cleaning of the Si substrate, germanium is synthesized on Si(100) through molecular beam epitaxy. The surface morphology is analyzed using reflection high-energy electron diffraction during synthesis and scanning electron microscopy after deposition. Main results. The work determines the temperature ranges at which the Si/Si(100) growth occurs due to the nucleation of islands, due to the movement of steps, and in combination. The effect of changing growth mechanisms on the size and density of Ge quantum dots on Si(100) is shown. Practical significance. The research results provide insight into the influence of growth mechanisms on the sizes of formed germanium quantum dots on silicon, which will make it possible to create nanophotonics and nanoelectronics elements with strictly specified parameters. (c) 2024 Optica Publishing Group

The paper presents the results of studying the dark currents of n B(SL) n structures with a superlattice (SL) in the barrier region based on Hg 1 – x Cd x Te grown by molecular beam epitaxy (MBE) in a wide range of experimental conditions. Dark currents were measured in the temperature range from 11 to 300 K for mesa structures with different cross-sectional diameters. The temperature dependences of the bulk component of the dark current density and the surface leakage current density are determined. It is shown that in the studied structures the current-voltage characteristics (CVCs) are formed by both the bulk and surface components of the current depending on the temperature and bias voltage.

Subject of study. The feasibility of applying superlattices as barrier layers in unipolar barrier nBn structures based on n-type HgCdTe [grown by molecular beam epitaxy (MBE)] for photodetection is investigated. Aim of study. This study aims to determine the influence of infrared optical radiation on the electrophysical characteristics of nBn structures based on HgCdTe (grown by MBE) with a superlattice in the barrier region. Method. Epitaxial Hg1-xCdxTe films, constituting nBn structures with a superlattice composed of 18 periods of Hg0.2Cd0.8Te (9 nm) and HgTe (2 nm), were grown by MBE. These films were then used to fabricate metal-insulator-semiconductor (MIS) structures. The photoelectric properties were investigated using admittance spectroscopy, both with and without 940-nm infrared light-emitting diode (LED) irradiation. Main results. Infrared optical radiation evidently affects the electrophysical characteristics of nBn structures based on HgCdTe (grown by MBE) with a superlattice in the barrier region. However, this influence does not mirror the behavior of classical MIS structures exposed to optical radiation, indicating that the superlattice contributes to the photoelectric properties of the studied structures. The observed effects are likely related to the recharging of energy levels (minibands) in the superlattice within the barrier region of the nBn structure. Practical significance. Since the application of superlattices in barrier nBn structures based on n-type HgCdTe is considered the most promising approach to eliminating the potential barrier for minority charge carriers, the results of this study may provide a foundation for developing photosensitive structure designs for the mid-and long-wave infrared ranges and for the subsequent creation of photodetector elements. (c) 2025 Optica Publishing Group

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

This study is devoted to the study of metal–insulator–semiconductor (MIS) structures based on n -HgCdTe (MCT) grown by molecular beam epitaxy (MBE) in the NBνN configuration, intended for the development of infrared (IR) detectors with reduced dark currents for MWIR and LWIR spectral ranges. Seven types of MIS structures have been studied by the admittance spectroscopy method. It is shown that the measurements of the frequency dependences of the impedance of MIS devices make it possible to accurately determine the differential resistance of the barrier structure. It has been established that for one of the studied structures, the values of the differential resistance are determined by the bulk component of the dark current, while the surface leakage component does not significantly affect the measured impedance. It is shown that if the problem of passivation of mesa structures is solved, it is possible to fabricate efficient MWIR and LWIR n B n , NBνN detectors based on MBE HgCdTe with high threshold parameters.

This paper presents the results of studying the processes of epitaxial growth of germanium on silicon with crystallographic orientation (111) in a wide temperature range. The temperature dependences of the duration of the transition stage from the 7 × 7 to 5 × 5 superstructure and the values of the critical thickness of the transition from two-dimensional to three-dimensional growth in the range from 250 to 700 °C are determined using the reflection high-energy electron diffraction method. It was shown for the first time that the transition time from the 7 × 7 superstructure to 5 × 5 superstructure depends on the temperature of epitaxial growth. The region of low temperatures of synthesis, which has received insufficient attention so far, is also considered.

The paper, which consists of two parts, considers in detail the method of discrete mobility spectrum analysis (DMSA) proposed by the authors as well as its application to determine the parameters of charge carriers in CdHgTe. The first part of the work was a brief review of the existing methods for analyzing the field dependences of the Hall coefficient and conductivity in structures with a multi-carrier spectrum of charge carriers. In the second part of the work, the physical properties of the mobility spectrum envelope in the mobility spectrum analysis (MSA) method are analyzed and the main idea, features, and algorithm of the DMSA method are presented. On the example of studying the electrical properties of numerous samples of CdHgTe epitaxial films, the high sensitivity of the DMSA was confirmed. Using DMSA, we analyzed a number of dependences of the conductivity tensor components σxx and σxy on the magnetic field B, available in the literature, and compared the results of the analysis with those obtained with other methods.

The study is devoted to an experimental analysis of the electrical and photoelectric characteristics of barrier photosensitive structures in the NBνN configuration based on n -HgCdTe. Seven different types of photosensitive structures for MWIR and LWIR infrared ranges, grown by molecular beam epitaxy, have been studied. The current–voltage characteristics were measured both in the dark and under illumination. The parameters of the NBνN structure, which realizes the maximum values of the photocurrent and the minimum values of dark currents in the operating range of bias voltages V for elevated operating temperatures, are determined.

Dark currents in medium-wave nBn structures based on HgCdTe grown with the aid of molecular beam epitaxy on the (013) GaAs substrates are studied. The passivation of the surface of the side walls of the mesastructures is performed using Al2O3 films formed by plasma atomic layer deposition. It is shown that the volume component of the dark current dominates in the nBn structures with a composition in the barrier layer of 0.84. The activation energy of the current is close to the band gap of the absorbing layer. Comparison of the experimental results with the results of the Rule07 empirical model shows that the diffusion limitation of the dark current takes place in the fabricated structures in a temperature interval of 180–300 K. The results indicate that the molecular beam epitaxy of HgCdTe on alternative substrates is a promising method for fabrication of unipolar barrier detectors for a spectral interval of 3–5 µm.

Two-dimensional materials have become one of the central research topics of scientists around the world after the production of graphene - a monatomic layer of carbon. Currently, two-dimensional crystals are among the most promising materials for next-generation nanoelectronics and photonics. The exploration of the feasibility of 2D materials devices causes a deeper insight into the physical properties of these new materials and provides a starting point for the development of a number of important practical areas. Over the past few years, researchers have been attracting increased attention from graphene-like materials of group IVA elements, such as silicene (Si), germanene (Ge), stanene (Sn), and plumbene (Pb). Experimental production and study of the unique properties of two-dimensional monatomic layers of carbon, silicon, germanium, tin and lead on various substrates created the prerequisites for the development of new generation devices based on them. The wide possibilities for controlling their exotic electronic, magnetic and optical properties through the choice of the substrate, the design and geometry of the two-dimensional layer, as well as by controlling the magnitude of elastic stresses, have made them a dominating topic for studying in the field of nanotechnology and materials sciences. This paper reviews the latest advances in growing silicene, germanene, stanene, and plumbene using epitaxial methods. Growth technologies for creation of high-quality two-dimensional structures of large area required for promising instrumentation area are considered in more details.

A detailed consideration of the discrete mobility-spectrum analysis (DMSA) method and its application to transport studies in HgCdTe is given. First, a brief review of the methods of the analysis of field dependences of the Hall coefficient and conductivity in HgCdTe-based structures with a multi-carrier mobility spectrum is presented. The advantages and drawbacks of these methods, which include original mobility-spectrum analysis by Beck and Anderson, multi-carrier fitting and iterative approach by Dziuba and Górska, and the later developments of these techniques, are considered. The properties of the envelope of the mobility spectrum are analyzed, and the specifics of DMSA are presented. Analysis of some magnetic-field B dependences of conductivity tensor components σxx(B) and σxy(B) presented in the literature is performed with DMSA, and the results are compared to those obtained with other methods.

Today, two-dimensional materials are one of the key research topics for scientists around the world. Interest in 2D materials is not surprising because, thanks to their remarkable mechanical, thermal, electrical, magnetic, and optical properties, they promise to revolutionize electronics. The unique properties of graphene-like 2D materials give them the potential to create completely new types of devices for functional electronics, nanophotonics, and quantum technologies. This paper considers epitaxially grown two-dimensional allotropic modifications of single elements: graphene (C) and its analogs (transgraphenes) borophene (B), aluminene (Al), gallenene (Ga), indiene (In), thallene (Tl), silicene (Si), germanene (Ge), stanene (Sn), plumbene (Pb), phosphorene (P), arsenene (As), antimonene (Sb), bismuthene (Bi), selenene (Se), and tellurene (Te). The emphasis is put on their structural parameters and technological modes in the method of molecular beam epitaxy, which ensure the production of high-quality defect-free single-element two-dimensional structures of a large area for promising device applications.

Mid-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy on GaAs (013) substrates were fabricated. The composition in the absorbing layer was 0.29, and in the barrier layer it was 0.67. It was shown that the dark currents of the created nBn structures are limited by the surface leakage component. To study the bulk component of the dark current, it was proposed to use the admittance measurements of test metal-insulator-semiconductor (MIS) devices based on fabricated nBn structures in the case of the formation of a backward contact to the absorbing layer. It was established that surface leakage does not affect the dynamic resistance of the MIS device barrier. The dependence of the dynamic resistance of the barrier layer (Rb) of the MIS device in the accumulation mode on the area of the front electrode (A), voltage, and temperature was determined. It was shown that, with the exclusion of surface leakage, the values of the RbA product in a temperature range of 230–300 K at forward biases are determined by the diffusion current of holes from the contact layer, and at reverse biases, by the diffusion current from the absorbing layer. It was found that at temperatures of 210–300 K, RbA values exceeding the values of this parameter determined according to the empirical model Rule 07 were realized in the fabricated structures.

Two types of long-wave infrared nBn structures based on mercury cadmium telluride grown by molecular beam epitaxy on GaAs (013) substrates have been fabricated. For each type of device, the side walls of the mesa structures were passivated with an Al2O3 dielectric film or left without passivation. The CdTe content in the absorbing layers was 0.20 and 0.21, and in the barrier layers, 0.61 and 0.63. The dark currents of the manufactured devices were studied in a wide range of voltages and temperatures. The values of the surface leakage component are found under various conditions. It has been shown that the surface leakage current density decreases upon passivation with an Al2O3 film. It was found that at room temperature in the fabricated nBn structures with reverse biases, the surface leakage component dominates, and with forward biases, the dark current is determined by the combined effect of the surface leakage component and the bulk current component. From the Arrhenius plots, the values of the activation energies of the surface leakage current component were found, which at small reverse biases are in the range from 0.05 to 0.10 eV. At small reverse biases, upon cooling the samples, the role of the bulk component of the dark current increases, which at 180 K is approximately 0.81 A/cm2. In the temperature range 200-300 K, the values of the dark current density exceed the values calculated according to the empirical Rule07 model by a factor of 10-100, which indicates the possibility of creating long-wave infrared barrier detectors with a decrease in the values of the surface leakage component.

Accumulation of arsenic implantation-induced donor defects in heteroepitaxial Hg1−xCdxTe structures with the composition of the active layer xa = 0.30 was studied with the use of the Hall-effect measurements and mobility spectrum analysis. The studies allowed for identifying the carriers in the implantation-damaged n+-layer, namely, electrons with low and intermediate mobility, and for establishing the dependence of their concentration on the ion fluence. The electrically active implantation-induced defects in the studied structures, similar to the case of those with xa = 0.22, were identified as atoms of interstitial mercury captured by dislocation loops and quasi-point defects. In the material with xa = 0.30, a weak dependence of the concentration of low-mobility electrons on the fluence was observed. In general, a substantial difference in the properties of p+–n junctions formed as a result of arsenic implantation in the structures with xa = 0.30 and xa = 0.22 was established. The difference was explained by the effect of the graded-gap surface layer on the diffusion of charged defects released during the implantation.

The admittance of test MIS structures based on nBn systems from Hg 1 – x Cd x Te grown by molecular beam epitaxy is investigated. Composition x in the absorbing and contact layers is 0.29; in the barrier layer, it is 0.60. An equivalent circuit of an MIS-structure based on an nBn system is proposed and the nominal values of the elements of this circuit are found under various conditions. Comparison of the temperature dependence of the barrier resistance with the Rule07 model indicates the possibility of creating efficient nBn detectors based on HgCdTe grown by molecular beam epitaxy for the 3- to 5-μm spectral range.

We analyze the current state of research in the field of creating unipolar semiconductor barrier structures based on various materials for infrared photodetector arrays, which make it possible to reduce the dark currents and thereby improve the threshold characteristics and ensure operation at high cooling temperatures. The main ways of minimizing a barrier for holes in the valence band are considered by the example of a photosensitive structure based on the n-CMT layer. It is shown that the nBn barrier structures are an alternative for creating photodiode sensing matrices for the mid- and far-infrared photodetector arrays.