Impurity Atoms Research Articles

Donor incomplete ionization and mobility enhancement in ultra-thin silicon-on-insulator films doped by phosphorus end-terminated polymers

The injection of P atoms is studied confining the same P dose in a progressively thinner silicon-on-insulator film. To account for the incomplete ionization observed in ultra-thin samples, the effect of Si/SiO2 interfaces must be considered.

Research progress of coincidence Doppler broadening of positron annihilation measurement technology in materials

Positron annihilation technique is an atomic-scale characterization method used to analyze the defects and microstructure of materials, which is extremely sensitive to open volume defects. By examining the annihilation behaviour of positrons and electrons in open volume defects, local electron density and atomic structure information around the annihilation site can be obtained, such as the size and concentration of vacancies, and vacancy clusters. In recent years, positron annihilation spectroscopy has evolved into a superior tool for characterizing features of material compared with conventional methods. The coincident Doppler broadening technique provides unique advantages for examining the local electronic structure and chemical environment (elemental composition) information about defects due to its effectiveness describing high momentum electronic information. The low momentum portion of the quotient spectrum indicates the Doppler shift generated by the annihilation of valence electrons near the vacancy defect. Changes in the peak amplitudes and positions of the characteristic peaks in the high momentum region can reveal elemental information about the positron annihilation point. The physical mechanism of element segregation, the structural features of open volume defects and the interaction between interstitial atoms and vacancy defects are well investigated by using the coincidence Doppler broadening technology. In recent years, based on the development of Doppler broadening technology, the sensitivity of slow positron beam coincidence Doppler broadening technology with adjustable energy has been significantly enhanced at a certain depth. It is notable that slow positron beam techniques can offer surface, defect, and interface microstructural information as a function of material depth. It compensates for the fact that the traditional coincidence Doppler broadening technique can only determine the overall defect information. Positron annihilation technology has been applied to the fields of second phase evolution in irradiated materials, hydrogen/helium effect, and free volume in thin films, as a result of the continuous development of slow positron beam and the improvement of various experimental test methods based on slow positron beam. In this paper, the basic principles of the coincidence Doppler broadening technique are briefly discussed, and the application research progress of the coincidence Doppler broadening technique in various materials is reviewed by combining the reported developments: 1) the evolution behaviour of nanoscale precipitation in alloys; 2) the interaction between lattice vacancies and impurity atoms in semiconductors; 3) the changes of oxygen vacancy and metal cation concentration in oxide material. In addition, coincident Doppler broadening technology has been steadily used to estimate and quantify the sizes, quantities, and distributions of free volume holes in polymers.

Surface morphology analysis of silicon doped with erbium atoms

This scientific work presents an analysis of the structural and electrical properties of light-emitting structures based on a single crystal of silicon doped with the rare earth element. As a result of thermal treatment of the initial samples at a temperature of 1200 ºC, it was found that the surface relief width of the sample decreased by 1.5÷2 times and the surface height increased by 3 times. According to the atomic force microscope analysis, it was found that n-Si<Er> samples have nanostructured surface defects with a surface relief width of 20÷300 nm and a height of 9÷42 nm. It was found that impurity atoms have a significant effect on the quantitative parameters of the initial sample atoms. As a result of the introduction of Er atoms into the control sample, it was determined that the number of technological impurities (O, C) increased by 10-15% by introducing one of the rare-earth elements (Er).

Development of enduring interstitial defects in Mg-doped CuO thin films.

Doping is one of the easiest methods to enhance the properties of semiconducting thin films. This work presents a systematic study of the influence of Mg doping on the optoelectronic properties of copper oxide (CuO) thin films prepared by spray pyrolysis. The pristine and doped films were prepared on glass substrates at an optimized temperature of 350 °C and a precursor solution concentration of 0.15 M while the Mg doping concentration was varied between 2 and 10 at%. The properties of the prepared films were studied in detail by using various characterization techniques such as X-ray diffraction, field emission scanning electron microscopy, Raman and photoluminescence, X-ray photoelectron spectroscopy and Hall measurement. The results suggest that oxygen interstitial (Oi) defects were enhanced upon doping which has influenced the properties of the film. The size of the crystallites reduced, and the band gap widened after doping. In addition, comprehensive density functional theory analyses have been conducted to gain a thorough understanding of the impact of impurity (i.e., doping/interstitial) atoms on the optical and electrical characteristics of CuO. This study shows that Oi defects improved the conductivity and enhanced the carrier concentration leading to an improvement in the electrical properties of the films.

Influence of Accumulation of Impurity Atoms Ni and Fe on the Electrophysical Properties of Si Single Crystals

Influence of Accumulation of Impurity Atoms Ni and Fe on the Electrophysical Properties of Si Single Crystals

In Ukrainian

The review material reveals the question of the influence of impurities on the physical properties of alloys, as well as the influence of gases on processes in alloys. It has been established that the presence of hydrogen affects diffusion in alloys, and gases have a significant effect on the thermoelectromotive force of metals. The paper describes the addition of a third element to binary systems, which can expand or narrow the domain of existence of an ordered phase. The above examples of adding an impurity of vanadium or molybdenum to an alloy of iron and chromium increase the ordering temperature. It has been established that gases can have a significant effect on the thermoelectromotive force of metals and increase the hardness and reduce the ductility of metals, as well as cause their brittleness and delamination. It has been established that hydrogen (H2) in alloys (for example, Fe-Ni and Au-Cu) affects diffusion and atomic ordering processes. Also, a small concentration of hydrogen, as an impurity, can change the electrical resistance of alloys (for example, in a Pd-Au alloy). It has been established that the addition of a third element to binary systems can change the state diagram, which must be taken into account when solving problems for the production of heat treatment modes for alloys, determining the conditions for phase equilibrium, etc. The paper considers the dependence of hydrogen solubility on temperature in metals (Cu, Fe and Al) and establishes the dependence of hydrogen solubility in a metal on the concentration of impurity metals. The temperature dependence of hydrogen solubility in Fe-V alloys is also shown. The shift of the density of state is studied for different distributions of impurity atoms in the alloy in the order-disorder system, and the dependence of the density of states of disordered and ordered solid solutions is studied. The dependence of the relative solubility of atoms introduced into the pores of alloys with an fcc structure (of the Cu3Au type) is indicated, taking into account the solubility, on the parameter χ, which is proportional to the degree of long-range order in the octahedral and tetrahedral pores of the alloys. The dependence of the relative solubility of intercalated atoms in octahedral pores of alloys with a bcc structure (such as CuZn and Fe3Al) is considered. A plot of the dependence of the concentration of dissolved impurity atoms on the degree of order is shown for substitutional alloys with a bcc lattice, where the M2 coefficient is introduced, which does not depend on the degree of order. The effect of pressure as a measure of long-range order is also studied, where its step decreases or increases, or decreases and then increases and vice versa (order-disorder phase transition). An equally important result is the graphic dependence of solubility (c) on pressure (P) in disordered and ordered alloys.

Intrinsic ferromagnetism in Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals at room temperature: Role of hybridization of impurity electronic states

We investigate room-temperature structural properties and spontaneous magnetism in a series of Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals grown by the Bridgman method. In order to elucidate the experimentally observed high-temperature magnetism in the studied systems, the dependencies of magnetization on magnetic field strength for the entire sample series were studied. Their detailed analysis revealed impurity contributions typical of ferromagnetic materials, which are described by magnetization curves with the parameters characterizing the spontaneous spin magnetism of the donor conduction electrons of the outer d-shells of the impurity atoms. According to the previously-developed theoretical concept, such a magnetic ordering mechanism stems from the direct exchange coupling of donor conduction electrons due to hybridization of impurity states, rather than from inter-impurity interactions. The results of optical emission spectroscopy and X-ray diffraction analysis confirmed the observed ferromagnetism to be intrinsic and linked directly to the d-electrons of iron impurity atoms.

Microstructure of High‐Chromium Ferritic–Martensitic Steels for Next‐Generation Reactors

High‐chromium steels are key alloys used for the construction of technological devices in industry. Stainless steels are suitable for components that are exposed to a corrosive environment for a long time because chromium has anticorrosion properties due to segregation of chromium and the formation of a passivation layer. The physicochemical properties of the surface and the bulk of the material as well are determined by microstructure. Herein, steel NS219 is focused on, where the chromium concentration is around 13.5 wt%. In order to study the microstructure of steel, Mössbauer spectroscopy is used. Experimental results are evaluated using the binomial distribution model of the probability distribution of atoms in the nearest neighbor of the resonant atom 57Fe. Obtained spectral parameters, viz., the average magnetic hyperfine field, the average isomer shift, and the probability of the atomic configuration with no impurity atoms in the two‐shell vicinity of the iron atoms, reach saturation values from which the solubility limit of chromium in iron can be determined. On the other hand, the solubility limit of iron in Cr‐rich phase can be estimated from the value of the isomer shift of the single‐line in the spectrum annealed for the longest time.

CO2 capture and storage by metal and non-metal decorated silicon carbide nanotubes: a DFT study

This study addressed the nano-mechanism of CO2 capture by Al-doped, B-doped and N-doped single-walled silicon carbide nanotubes (SWSiCNTs) using the prominent density functional theory. The results showed absolute interactions between CO2 and B- and N- impurity atoms of the SWSiCNT surface with the highest adsorption energy of −1.85 eV and −1.83 eV respectively. Analysis of the binding energy of CO2 to Al-doped SWSiCNT revealed that chemisorption between them is stronger than B-doped and N-doped SWSiCNTs. Results from optical adsorption spectra revealed that both B-and N-doped systems adsorb CO2 in the visible region of the electromagnetic spectrum while B-doped SiCNT shows the highest adsorption. This study recommends B- and N-doped SiCNTs as candidates for CO2 capture and storage with higher efficiency by B-doped SiCNT, while the performance of the Al-doped system was underscored.

The Mechanism of the Formation of Binary Compounds Between Zn and S Impurity Atoms in Si Crystal Lattice

The paper presents the results of an experimental study of surface morphology, elemental composition, electrophysical and optical properties of Si samples earlier doped with impurity atoms of Zn and S. The results of the study revealed a sufficient concentration of Zn and S elements on Si surface after diffusion (3.1% and 2.6% by weight, respectively). After additional thermal treatment at different temperatures, i.e., at 850°C and 875°C, the samples of I group have regained their initial parameters. However, it’s noteworthy that the mobility of charge carriers in group I samples was comparatively lower than that in group II samples allegedly under the influence of Zn and S binary molecules. After additional heat treatment of all samples at a temperature of 875°C, the authors have studied optical absorption coefficients. And their band gap energies were determined using the Tauc Plot method. According to the results of the study, the optical band gaps in group II and III samples were 1.12 eV, whereas the band gap energy in group I samples after additional thermal treatment at a temperature of 875 °C turned out to be 1.31 eV. Having theoretically calculated the band gap by applying Vegard’s law, the authors suggested that the new structure must be of Si0.92ZnS0.08 - type.

Method for Low-Temperature Vacuum-Thermal Cleaning of Surface Single Crystals Si and GaAs

The paper reports on a method of low-temperature vacuum-thermal cleaning of the surface of Si and GaAs single crystals developed by the authors, which consists in implanting Ba+ ions (or alkaline elements) into Si and GaAs crystals preliminarily cleaned by ultra-high vacuum by ion etching and subsequent annealing in two stage at 800 K - 15 minutes and at 1000 K for 30 minutes. The effect of effective cleaning is achieved due to the fact that the introduced ions of Ba+ and alkaline elements, being active, form compounds with impurity atoms (O, C, S, N, etc.) at the first stage and are removed together with impurities after the second stage of heating.

Electronic and magnetic performance of MoS2 monolayer via Tc & Nb impurities defect and water adsorption

This study examined the effect of Tc & Nb impurity atoms on MoS2 (Tc-MoS2 & Nb-MoS2 ), and adsorption of water molecule on impurities defected MoS2 (Tc-W-MoS2 & Nb-W-MoS2) material from first-principles calculations. By the estimation of their ground state energy and binding energy, they are stable 2D materials. From band structure and density of states (DoS) calculations, Tc & Nbimpurities affect the nature of pristine MoS2. It is found that Tc-MoS2 has n-type & Nb-MoS2 has p-type semiconducting nature. Water interaction on Tc-MoS2 & Nb-MoS2 slightly changes the electronic properties and impacts the bandgap, which enhanced the electronic performance of material than that of pristine MoS2. The magnetic properties of Tc-MoS2, Nb-MoS2, Tc-W-MoS2, and Nb-W-MoS2 are analyzed and found to exhibit an uneven distribution of up-spin and down-spin states of electrons in the orbital of atoms near the Fermi level. It reflects that they have magnetic properties. The non-magnetic MoS2 material changes in to weak magnetic defected-MoS2 materials due to the presence of Tc, Nb and adsorbed water molecule. It means, impurity defects add to magnetic properties of pristine MoS2. Magnetic properties on defected MoS2 occurred due to the dominant contributions of spin states of 4d-orbital of Mo, Tc, Nb atoms, and 3p-orbital of S atoms in the structures. This study highlights the impact of Tc & Nb impurity atoms and adsorbed water molecule on impurities defected MoS2. The studied materials have potential applications in the fields of catalysis, nanoelectronics, biomedicine, and magnetic sensors on the basis of their electronic and magnetic properties.

Alloy splitting of the FeGa acceptor level in dilute AlxGa1−xN

The results of conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS measurements of the FeGa(0/−) acceptor level in dilute AlxGa1−xN layers (x ≤ 0.05) grown by MOVPE technique (metal–organic vapor phase epitaxy) on native ammono-GaN substrates are analyzed and discussed. It is shown that the electron emission signal related to the FeGa acceptor level in AlxGa1−xN splits into individual components due to aluminum fluctuations in the second-nearest neighbor (2NN) shell around the FeGa impurity atoms. The calculations of the probability of finding a given number of aluminum atoms in the 2NN shell of the FeGa defect agree well with the experimental concentrations determined from Laplace DLTS peak intensities. This finding shows that in dilute AlxGa1−xN layers grown by MOVPE, aluminum and iron atoms are randomly distributed in the material. Finally, we demonstrate that the energy level of the FeGa acceptor with no Al atoms in the 2NN shell in the AlxGa1−xN samples shifts linearly with the aluminum content and the shifts are 28 and 55 meV relative to that in GaN for the samples with x = 0.025 and 0.05, respectively.

The effect of non-metals (O, F) dopant on the electronic structure, Dirac cone, and optical characteristics of graphene sheets applicable for gas sensing

In order to gain a systematic comprehension of the impacts of low-level defects in graphene, ab-initio calculations were performed on monolayer graphene sheets to examine how oxygen and fluorine substitutional impurities affect their energetic stability, electronic and optical characteristics. The optimal configurations, structural stability, electronic band structures, spatial charge density, and optical spectra of graphene single-layer materials doped with oxygen and fluorine atoms are investigated. The fluorine-doped graphene, therefore, showed a lower formation energy than its oxygen-doped counterpart. Additionally, F-doped graphene shows a higher charge density around the fluorine atom than O-doped graphene. Based on band structure analysis, the lower conduction bands of graphene sheets shift below the Fermi state (EF) when two O or F impurities are substituted into it. With two O/F impurity atoms doped into graphene, the conduction states are farther displaced below the EF, resulting in n-type behavior. Consequently, altering graphene structure via an O/F-substituting scheme results from the disruption of the Dirac cone near EF, which has become flat along the high symmetry point (K-point) in the Brillouin zone. Furthermore, the substitution of graphene sheets via O or F impurities exhibit markedly modified optical spectra and refractive indices at low photon energies. As a result, with one or two O/F impurity elements inserted into graphene sheets, the reflectivity and optical conductivity spectra differ at the lowest electromagnetic radiation ranges. Additionally, the electron energy loss functions as well as X-ray absorption spectra of clean and doped graphene monolayers revealed spectral variations at a moderate energy span. These investigations surmise that novel chemical modifications to graphene sheets doped with light non-metallic elements (O/F) may offer the opportunity to tailor their optical characteristics in the infrared spectrum, which may be beneficial in sensor and electrocatalyst uses.

Theoretical Study of Doping in GaOOH for Electronics Applications

GaOOH, having a bandgap of 4.7–4.9 eV, can be regarded as one of several ultrawide-bandgap (UWBG) semiconductors, although it has so far mainly been used as a precursor material of Ga2O3. To examine the possibility of valence control and application in electronics, impurity levels in GaOOH are investigated using the first-principles density-functional theory calculation. The density values of the states of a supercell including an impurity atom are calculated. According to the results, among the group 14 elements, Si is expected to introduce a shallow donor level, i.e., a free electron is introduced. On the other hand, Ge and Sn introduce a localized state about 0.7 eV below the conduction band edge, and thus cannot act as an effective donor. While Mg and Ca can introduce a free hole and act as a shallow acceptor, Zn and Cd introduce acceptor levels away from the valence band. The transition metal elements (Fe, Co, Ni, Cu) are also considered, but none of them are expected to act as a shallow dopant. Thus, the results suggest that the carrier concentration can be controlled if Si is used for n-type doping, and Mg and Ca for p-type doping. Since GaOOH can be easily deposited using various chemical techniques at low temperatures, GaOOH will potentially be useful for transparent electronic devices.

Self-Oscillating Processes in Silicon, Problems and Prospects of Research and Their Application in Electronics

The study of self-oscillating processes in semiconductors and semiconductor structures makes it possible to create a physical mechanism for these unique phenomena and shows the possibilities of creating solid-state generators and sensors of physical quantities with the frequency-amplitude output. From the analysis of the literature data, it was found that the excitation conditions and the parameters of current self-oscillations were studied in more detail only in silicon doped with manganese and zinc atoms, as well as in CdSe, CdS, InGa semiconductor compounds and in some other structures. In other materials, the boundary regions of the existence of the current instabilities depending on external factors were not very precisely determined. This led to the absence of reproducible results and inconsistencies in the correlation between the electrophysical parameters of the material with the parameters of current self-oscillations (amplitude, frequency). In this regard, this article presents a comprehensive study of current self-oscillations in silicon doped with impurity atoms of manganese, zinc, sulfur, and selenium. A physical mechanism of self-oscillations of the current is proposed, which has a good agreement with the experimental results obtained not only in the studies of the authors but also with the experimental results of other researchers.

Modulating impurity levels in two-dimensional polar materials for photocatalytic overall water splitting

Doping to induce suitable impurity levels is an effective strategy to achieve highly efficient photocatalytic overall water splitting (POWS). However, to predict the position of impurity levels, it is not enough to only depend on the projected density of states of the substituted atom in the traditional method. Herein, taking in phosphorus-doped g-C3N5 as a sample, we find that the impurity atom can change electrostatic potential gradient and polarity and then significantly affect the spatial electron density around the substituted atom, which further adjusts the impurity level position. Based on the redox potential requirement of POWS, we not only obtain suitable impurity levels but also expand the visible light absorption range. Simultaneously, the strengthened polarity induced by doping further improves the redox ability of photogenerated carriers. Moreover, the enhanced surface dipoles obviously promote the adsorption and subsequent splitting of water molecules. Our study provides a more comprehensive view to realize accurate regulation of impurity levels in doping engineering and gives reasonable strategies for designing an excellent catalyst of POWS.

Standing wave patterns in graphene systems studied using scanning tunneling spectroscopy

Standing wave patterns are formed near potential barriers or steps due to the interference of incident and reflected waves. Graphene systems show standing wave patterns near atomic step edges, defects, and impurities in scanning tunneling microscopy; however, there are still unexplored examples. In this study, we present our experimental results for graphene directly grown on hexagonal-BN/Cu by chemical vapor deposition. Standing wave patterns were observed in our scanning tunneling microscopy and spectroscopy, revealing linear dispersion relations with a Fermi velocity of about 106 m/s. Our study shows that graphene grown on hexagonal-BN/Cu provides a useful platform to study the electronic characteristics of graphene systems.

Host isotope effects on the oxygen local vibrations in CdTe

Strong absorption peak observed near 350 cm−1 in the infrared spectrum of CdTe is assigned to a localized vibrational mode of 16O impurity atoms at tellurium sites. In this work, we studied the nature of these vibrations in terms of the effect of isotopic mass variations in the nearest neighbor Cd atoms. We showed that Cd atoms with 8 stable natural isotopes of varying abundances cause the observed line shape in the observed localized vibrational absorption peak. To calculate the effect of isotopic mass variations, we used the XY4 molecular model, X being the impurity atom at a host Te atom site and Y’s are various isotopes of the host Cd atoms. Corresponding frequencies of local modes were calculated for each possible combinations of neighboring Cd atoms. For an XY4 molecule with Td symmetry, only the triply degenerate mode is infrared active. The energies of this mode are higher than those of the others. This mode is possible only when all neigboring Cd atoms are the same isotope. To simulate the absorption data, we used a dynamical matrix approach where a force constant is given for each of the bending and stretching potential energy terms. By diagonalization of the dynamical matrix we were able to fit the calculated spectrum to the data with a proper choice of the bending and stretching force constants. A good agreement with the experiment as well as reported force constants for other impurities in CdTe is obtained.

First-principles study of hydrogen capture, solution and mechanical effects in transition metal tungsten alloy W-TM (V, Nb, Ta)

Tungsten alloy as a candidate for plasma facing materials (PFMs) in thermonuclear fusion experimental reactor (Tokamak) is of great significance for the successful use of nuclear fusion. Therefore, it is worth exploring to understand the problems of solution and retention of hydrogen (H) and its isotopes in transition metal (TM) and tungsten (W) forming isotype alloys. Based on density functional theory, the effects of hydrogen solution in W-TM (TM = V, Nb, Ta) alloy on energetics, bond length, electronic structure and mechanical properties are studied by first-principles calculations. The calculated solution energy indicates that a single H atom is more easily trapped by tetrahedral interstitial sites in the W-TM alloy, and WV alloy has the strongest trapping ability for single H atoms and the strongest interaction between them. With the increase of H impurity atoms, H is more likely to form aggregation in W-TM. The accumulation of multiple hydrogen impurities will cause serious fluctuations in the mechanical properties and melting point of W-TM alloy, among which WV alloy is least affected by H accumulation and has a strong ability to resist the effect of H accumulation. The results can provide a reference for understanding the behavior of H in the plasma facing material.