Georgiy Yu. Sidorov

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 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 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.

Subject of study. The focus of this study is the spatial resolution of n-on-p linear focal-plane-array detectors based on mercury–cadmium–telluride material and modified by introducing into their structure a grid guard diode with floating n-region potential. The aims of the study are to perform an analysis of the influence of a grid guard diode with floating n-region potential on the line spread and modulation transfer functions of the linear n-on-p photodetectors. Moreover, the possibility of using structural defects in the examined photodetectors is investigated for implementing a continuous action of the guard diode as a sink for photogenerated charge carriers. Method. The diffusion of photogenerated charge carriers in the absorber layer of focal-plane-array detectors is modeled using the Monte Carlo method. Furthermore, the spatial resolution of such photodetectors is experimentally investigated by performing spot-scan measurements and calculating the modulation transfer function of photodetector structures. Main results. The presence of the grid diode with floating n-region potential in the structure of n-on-p photodetectors broadens the base and decreases the width of the upper part of the line-spread-function peak of linear focal plane arrays with the corresponding modification of the modulation transfer function. However, overall, no significant improvement is observed in the resolution of the modified photodetector structure. Practical significance. The results of this study indicate that the guard diodes in the photodetectors must be grounded. These results can also be used in the development of methods for optimizing and enhancing the spatial resolution of focal-plane-array detectors.

The effect of HgCdTe oxide on the electro- physical properties of the HgCdTe/Al2O3 interface has been investigated. The HgCdTe oxide was formed by pretreatment after wet etching in Br/HBr. Five samples with different surface treatments of HgCdTe after wetting chemical etching in Br/HBr were produced. The treatments were focused on changing the thickness of the HgCdTe native oxide. It was found for all samples that the difference between the flat band position voltages for the forward and reverse sweep increased when the voltage range was increased. The sample oxidized for a day in H2O2 vapor had the smallest difference between the positions of the flat bands. This indicates the smallest number of slow states in the intermediate layer on the HgCdTe/Al2O3 interface. In all samples, a flat band voltage had a shift. It indicated the presence of fixed built-in charge in the dielectric and/or intermediate layer. The HgCdTe series resistance was observed to affect the result when the measuring frequency was increased. The lowest value of the surface states density in the sample pretreated with TMA vapor without oxidation phase before Al2O3 growth was observed.

A prototype of a metal–insulator–semiconductor field-effect transistor based on PbSnTe:In/(111)BaF2 film with an Al2O3 gate dielectric was designed for the first time. With the gate voltage applied in the range – 7.7 V < Ugate < +7.7 V the relative modulation in the drain-source current Ids/Ids attained near five-fold change at T = 4.2 K. When illuminated with rela-tively low (~100 photon/s) fluxes, negative photoconductivity was detected accompanied with a decrease in Ids by ~104 times and a simultaneous decrease in Ids by ~103 times or even more. The estimated detectivity was about 71016 cmHz0.5W-1 at a wavelength  about 25 micron with the accumulation time about 0.5 s. A qualitative model is discussed which assumes the ex-istence of deep traps and a photo-capacitance effect.

We investigate the HfO₂/Hg_0.78Cd_0.22Te interface fabricated by plasma-enhanced atomic layer deposition (PEALD) at 120 °C During the deposition of HfO₂, no donor-like defects are introduced into mercury cadmium telluride. X-ray photoelectron spectroscopy and ellipsometry were used to establish the optimal process regime at 120 °C and to demonstrate how HfO₂ layer composition and growth rate per cycle depend on post-plasma purge time; the optimum is achieved at 6 s. Increasing the post-plasma purge time decreases the carbon and nitrogen impurity concentration in the HfO₂ layer. Measurements of the admittance of metal-insulator-semiconductor (MIS) structures over the surface of a sample show that the electro-physical properties are uniform. We discuss the method of measuring the admittance of MIS structures that allows us to minimize the contribution of slow states with trapped charge on shape and shift of the C–V curve. The results demonstrate that the densities of fixed charge, slow states, and fast interfacial traps at the HfO₂/MCT interface are greater than that for Al₂O₃/MCT (also formed by PEALD). The interface trap density is estimated from a normalized parallel conductance map, and the HfO₂ film adheres well.

Предложен метод определения частотно-контрастной характеристики (ЧКХ) инфракрасного (ИК) объектива. Излучение выходной щели монохроматора с определённой длиной волны фокусировалось с помощью исследуемого объектива в виде длинной узкой освещённой полоски на холодном металлическом экране с апертурной щелью. Применение щелевой измерительной апертуры вместо точечной для сканирования изображения источника позволило увеличить полезный сигнал и использовать в качестве источника излучения выходную щель монохроматора. Вместо одиночного ИК-детектора с малой фоточувствительной площадью использовался апертурированный матричный ИК-фотоприёмник. С помощью средне- и длинноволновых фотоприёмных матриц формата 320 × 256 на основе выращенных с применением молекулярно-лучевой эпитаксии слоёв материала кадмий-ртуть- теллур были измерены функции рассеяния линии и ЧКХ ИК-объективов средне- и длинноволнового ИК-диапазонов спектра. Дано сравнение экспериментальных результатов с дифракционной ЧКХ изученных...