Alexander V. Voitsekhovskii

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.

The results of investigations of metal‒insulator‒semiconductor structures based on an n-HgCdTe nBn structure with a superlattice in the barrier region are reported. The admittance spectroscopy study, which allows determination of a variety of properties of semiconductor heterostructures, has been carried out in a wide temperature range. The frequency and voltage dependences of the admittance and the time dependences of the relaxation of the electric capacitance under a pulsed bias have been obtained. The temperature dependence of the majority carrier concentration has been established. Using the temperature dependences of the longitudinal resistance of the epitaxial film volume and the majority carrier concentration, the activation energies have been found. The effect of IR illumination on different characteristics of the structure has been analyzed. It is shown that constant IR illumination changes the capacitance level in both the inversion and enrichment modes.

The admittance characteristics of a metal‒insulator‒semiconductor structure with an nBn semiconductor structure based on the MBE Hg_1 ‒ xCd_xTe epitaxial layers with a superlattice in the barrier region have been investigated. The temperature dependences of the majority carrier concentration and the product of the differential resistance of the space charge region and the structure area have been plotted. The parameters of the Al₂O₃/Hg_1 ‒ xCd_xTe interface, including the density and characteristic time of recharging of surface states, have been determined. It has been found that the temperature dependence of the differential conductivity of the space charge region contains two groups of maxima, the positions of which have been used to determine the carrier activation energies, one of which corresponding to the contact layer band gap.

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 Hg_1−xCd _x Te films, constituting nBn structures with a superlattice composed of 18 periods of Hg_0.2Cd_0.8Te (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.

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.

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 J_B and the surface leakage current component J_S 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 J_B over J_S is shown throughout the entire range of bias voltages and temperatures studied.

Subject of study. The application of superlattices as barrier layers in unipolar barrier nBn structures based onn-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 Hg_1−x Cd_xTe 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.

The paper presents the results of studying the dark currents of nB(SL)n structures with a superlattice (SL) in the barrier region based on Hg_1 – xCd_xTe 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.