In this work, the spectra of optical constants of epitaxial layers of cadmium telluride near the fundamental absorption edge are studied. For this purpose, ellipsometric measurements of the layers under study were carried out in a vacuum chamber in the temperature range from T = 38–275°C. A numerical algorithm has been developed for solving the inverse ellipsometry problem for the structures under consideration, with the help of which the spectral dependences of the refractive index n(λ) and absorption index k(λ) are determined in the wavelength range from 700 to 1000 nm. The parametric dependences of k(λ, T) in the fundamental absorption region and in the transparency region are presented. The presence of an extended absorption tail in the transparency region was established, presumably associated with imperfections in the crystal structure.

The mechanisms of conductivity in metal-insulator-semiconductor (MIS) structures based on [GeOx]((z))[SiO2]((1-z)) films (0.25 <= z <= 1) fabricated by co-evaporation of germanium oxide and silicon oxide powders in vacuum and deposition on a p(+)-type silicon substrate are studied. Indium tin oxide deposited by magnetron method is used as the top electrode. According to IR spectroscopy, Ge-O, Si-O, and Ge-O-Si bonds are detected in the films, while no features related to the presence of germanium clusters are found in the Raman spectra. The current-voltage characteristics (I-V curves) are measured at different temperatures and analyzed by applying the eight most common models of charge transport in MIS structures. It is found that the experimental I-V curves are most accurately approximated in the space charge limited current model, and the parameters of the charge traps are determined within this model.

The problems of in situ ellipsometric control during the growth of ZnTe and CdTe buffer layers intended for cadmium-mercury-tellurium epitaxy are considered. It has been established that for 20 nm ZnTe layers the spectral dependences of the optical constants near the absorption edge are smoothed, which indicates the presence of structural defects in the film. It has been shown that the microrelief of the CdTe growth surface is a criterion for the structural perfection of the layers and can be measured using an ellipsometer both at the early stages and during steady-state growth.

Photoluminescence (PL) and photoreflectance (PR) spectroscopy were used for the optical study of arsenic doping of HgCdTe grown by molecular beam epitaxy (MBE). Un-doped and arsenic-doped material with cadmium telluride molar fraction x=0.29 grown under similar conditions and subjected to similar types of annealing was studied. The PL spectra of the un-doped material featured signatures of intrinsic defects associated with mercury vacancy, excessive tellurium, and related complexes. In the arsenic-doped material, optical signatures of these defects appeared to be suppressed. After arsenic activation, shallow (7-8meV) acceptor levels were found in the material. These were attributed to the dopant activation, which was confirmed with electrical studies showing p-type conductivity with hole concentration similar to 10(16) cm(-3). The studies showed that the actual pattern of arsenic doping in HgCdTe can be indeed screened by intrinsic defects, which are inherent to MBEgrown HgCdTe and tend to interact with the dopant.

Subject of study. An alternative substrate for the growth of a mercury-cadmium-telluride ternary compound is studied, which consists of silicon with CdTe and ZnTe layers deposited on it. Aim of study. . The aim is the construction of a model of the rough surface of CdTe films to create a technique for quality control of the growing structures. Method. Non-destructive methods with sufficient resolution are required as roughness measurement techniques. These conditions are satisfied by optical research methods. In this work, ellipsometry and interference profilometry were used. Main results. The roughness of CdTe films was studied using ellipsometry and interference profilometry. It is shown that these two methods perfectly complement each other and provide a more complete picture of the profile surface than each one separately. A two-scale model of the rough surface of CdTe buffer layers representing a slightly wavy surface with a small-scale relief superimposed on it has been constructed. It is shown that the ellipsometric measurements are affected by the small-scale relief. This result was used to develop a technique for controlling the process of epitaxial growth of buffer layers. Practical significance. The results of studying the surface roughness of CdTe films obtained in this work serve as the basis for the development of methods for controlling the parameters of CdTe layers suitable for growing high-quality photosensitive structures. (c) 2024 Optica Publishing Group

Chemical pretreatment and surface cleaning is a key procedure of semiconductor technologies. Development of methods for the preparation of mercury cadmium telluride (HgCdTe) surfaces is of interest because this material has a wide range of known and potential applications in photoelectronics. This work reports an XPS and AFM study of the effect of various chemical treatments on the chemical composition and micro-morphology of the HgCdTe surface. Among all considered etchants, only ammonium hydroxide effectively removes the native oxide of HgCdTe without leaving a surface layer of metallic tellurium, while preserving nearly stoichiometric chemical composition of the surface. The optimal time of aqueous ammonia treatment is determined.

Предварительная химическая обработка и очистка поверхности является одной из ключевых операций в полупроводниковых технологиях. Развитие методов подготовки поверхности теллурида кадмия–ртути (КРТ, HgCdTe) является актуальной задачей в связи с широким спектром существующих и потенциальных применений этого материала в фотоэлектронике. С помощью методов РФЭС и АСМ в работе исследовалось влияние различных химических обработок на химический состав и микрорельеф поверхности HgCdTe. Среди всех рассмотренных травителей только водный аммиак эффективно удаляет собственный оксид КРТ, не оставляет поверхностного слоя металлического теллура, и обеспечивает близкий к стехиометрии химический состав поверхности. Предложено оптимальное время обработки в водном аммиаке.

In situ temperature control is required to obtain HgCdTe layers of high crystalline perfection by molecular beam epitaxy. To solve this problem, we used spectroscopic ellipsometry. Various methods have been developed for measuring the temperature before the start of epitaxy. They are based on the analysis of different regions of the ellipsometric spectra of the CdTe buffer layer. An experimental comparison of the suggested methods shows that the temperature measurement accuracy is several degrees, and the sensitivity reaches fractions of a degree. At the stage of stationary growth of layers, it is possible to determine the change in temperature and composition from the kinetics of ellipsometric spectra. Ellipsometric measurements made during the growth of HgCdTe with a sharp change in the heating regime showed correlated changes in both temperature and composition.

The interface between Cd 0.22 Hg 0.78 Te and HfO 2 grown by plasma-enhanced atomic layer deposition at a temperature of 120 o C in a specifically optimized deposition mode has been studied. The method used in this work for measuring the admittance of metal-dielectric-semiconductor structures made it possible to establish that their electrophysical parameters are uniform over the sample surface. The spectrum of fast surface states density at the HfO 2 -Cd 0.22 Hg 0.78 Te interface has been calculated. Keywords: CdHgTe, HfO 2 , ALD, C-V, passivating coating.

We investigate the HfO2/Hg0.78Cd0.22Te 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.

An ellipsometric technique has been developed which makes it possible to observe changes in the composition and temperature of cadmium--mercury--tellurium layers during their growing by molecular beam epitaxy. The technique was tested for diagnostics the variations of the composition and the temperature during layer growth in the mode of constant power of the substrate heater and with its sharp change. It was found that the drop in power and a following decrease in the growth temperature were also accompanied by a monotonic decrease in the composition. In the case of a constant heater power, a slight increase in the sample temperature was observed with an almost unchanged composition of the growing layer. Keywords: ellipsometry, mercury--cadmium--telluride, in situ control, epitaxial growth, temperature.

The interface between Cd0.22Hg0.78Te and HfO2 grown by plasma-enhanced atomic layer deposition at a temperature of 120 ℃ in a specifically optimized deposition mode has been studied. The method used in this work for measuring the admittance of metal-dielectric-semiconductor structures made it possible to establish that their electrophysical parameters are uniform over the sample surface. The spectrum of fast surface states density at the HfO2 - Cd0.22Hg0.78Te interface has been calculated.

The problem of in situ temperature control during the growth of epitaxial layers of HgCdTe by molecular beam epitaxy is considered. Various approaches to solving the problem using spectroscopic ellipsometry are proposed. They are based on the temperature dependence of the optical constants spectra of the CdTe buffer layer and the growing HgCdTe layer. The results of experimental testing of these methods are presented, which show that the temperature measurement accuracy is several degrees, and the sensitivity reaches fractions of a degree. At the stage of stationary growth, it is possible to determine the change not only in the temperature, but also in the composition of the growing layer from the ellipsometric spectra.

Для применения тройного раствора CdHgTe в прикладных задачах необходимо подобрать для него хорошее пассивирующее покрытие. Пассивирующие покрытия характеризуется рядом параметров: плотностью поверхностных состояний, однородностью и величиной встроенного заряда в диэлектрической плёнке и др. В работах, исследовавших границу раздела гетеро-эпитаксиальных структур (ГЭС) CdHgTe выращенного методом молекулярно-лучевой эпитаксией (МЛЭ) и Al2O3, нанесенного методом плазменно-индуцированного атомно-слоевого осаждения (ПАСО) при температуре образца 120°С, отмечается, что данный диэлектрик обладает хорошими пассивирующими свойствами [1, 2]. Известно, что стехиометрия и количество примесей в Al2O3, выращенного методом ПАСО, достигает оптимума при температурах 200-300 °С [3]. С другой стороны, с поверхности CdHgTe, в вакууме, начинает испаряться ртуть уже при 80 °С [4]. В литературе не встречается работы, в которых проводились исследования по поиску оптимальных параметров роста Al2O3, выращенного методом ПАСО, на CdHgTe. Цель данной работы – исследование параметров пассивирующих слоев Al2O3, выращенного методом ПАСО на CdHgTe при различных температурах и обработках CdHgTe перед ростом диэлектрической плёнки.

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.

На основе проведeнных in situ и ex situ эллипсометрических измерений найдены спектральные зависимости температурной чувствительности оптических постоянных Hg1-xCdxTe --- dn(λ) и dk(λ) для серии образцов разного состава в диапазоне от 0.160 до 0.327. Эксперименты были проведены в процессе остывания выращенных образцов в вакуумной камере. Установлено, что полученные зависимости dn и dk хорошо аппроксимируются суммой трeх осцилляторов Лоренца с добавлением дисперсионных слагаемых формулы Коши. Предложена параметрическая модель, которая описывает чувствительности dn(λ) и dk(λ) для произвольного состава x в указанном диапазоне вблизи температуры роста. Проведенные ex situ температурные измерения вблизи комнатной температуры коррелируют с данными высокотемпературных измерений. Полученные результаты актуальны для разработки эллипсометрических методов контроля in situ процессов роста слоeв Hg1-xCdxTe. Ключевые слова: кадмий-ртуть-теллур, эллипсометрия, спектры оптических констант, температурная чувствительность, молекулярно-лучевая эпитаксия.

Low temperature in situ control in the technology of HgCdTe layers growing by MBE is a key requirement for obtaining structures of high quality. Spectroscopic ellipsometry seems to be one of the suitable technique for solving this problem. The present paper proposes ellipsometric methods for determining the temperature in the process of pre-epitaxial heat treatment of the samples. The proposed methods are based on the temperature dependence of the optical constants spectra of the CdTe buffer layer. The first method uses the temperature shift of the absorption edge, which is determined from the onset of interference oscillations. It turned out to be resistant to experimental errors and its accuracy proved to be 3-5 degrees C. The second method is based on comparing the measured and reference spectra. It is much more sensitive to the temperature, but depends strongly on the accuracy of ellipsometric measurements. The combined use of both methods ensures a temperature sensitivity of the order of 1 degrees C and an accuracy of 3-5 degrees C.

Based on in situ and ex situ ellipsometric measurements, the spectral dependences of the temperature sensitivity of the optical constants Hg 1 –   x Cd х Te— dn (λ) and dk (λ) have been found for a series of samples of different compositions in the range from 0.160 to 0.327. The experiments were performed during cooling of the grown samples in a vacuum chamber. It has been found that the obtained dn and dk dependences can be well approximated by the sum of three Lorentz oscillators with the addition of the dispersion terms of the Cauchy formula. A parametric model that describes the sensitivities dn (λ) and dk (λ) for an arbitrary composition x in the specified range near the growth temperature has been proposed. Ex situ temperature measurements performed near room temperature correlate with the data of the high-temperature measurements. The results obtained are relevant for the development of ellipsometric control methods in situ of Hg 1 –   x Cd х Te layer growth processes.

Разработана эллипсометрическая методика, позволяющая наблюдать за изменениями состава и температуры слоeв кадмий--ртуть--теллур в процессе их выращивания методом молекулярно-лучевой эпитаксии. Методика опробована для диагностики состава и температуры при выращивании слоeв в режиме постоянной мощности нагревателя подложки и при еe резком изменении. Установлено, что падение мощности и последующее уменьшение температуры роста сопровождается также монотонным уменьшением состава. В случае постоянной мощности нагревателя наблюдается незначительное увеличение температуры образца при практически неизменном составе растущего слоя. Ключевые слова: эллипсометрия, кадмий--ртуть--теллур, HgCdTe, состава, in situ контроль температуры, эпитаксиальный рост.

Films of n-Hg0.775Cd0.225Te with near-surface wide-gap layers were grown by molecular beam epitaxy on Si (013) substrates. To measure the admittance, metal – insulator – semiconductor (MIS) structures were fabricated on the basis of the as-grown HgCdTe film, films after implantation, and films after implantation and annealing. Using techniques that take into account the presence of graded-gap layers and slow interface states, the main parameters of the near-surface layers of HgCdTe films have been determined after the technological procedures used to create photodiodes.