Papers by Keyword: Point Defect

Abstract: Initially, this work briefly outlines how ultrasound can modify and characterize the defect system in semiconductors. Then, the study experimentally examines the effect of different types of acoustic waves on the association of FeB pairs in monocrystalline silicon. The results reveal that as the frequency of longitudinal waves increases, the ultrasound's effectiveness in accelerating the association rate decreases. Conversely, exciting transverse waves show the opposite trend. The study also assesses the potential to obtain a positron-annihilation response from the FeB complex in silicon, highlighting the advantages of conducting such measurements under ultrasound loading of the crystal.

Abstract: The high sensitivity of positrons to directly probe atomic scale defects revealing their structure and characteristics makes it a unique tool in materials science research covering all types of materials from hard to soft matter. This review focuses on applications of positron annihilation spectroscopy (PAS) in hard materials. However, it is not intended as a comprehensive review of the foundations of positron annihilation spectroscopy and description of its techniques. These exist in numerous publications cited in this review. Instead, the aim here is to facilitate employing PAS and interpretation of its measurements by illustrating the advantages, limitations, and challenges and guiding the reader on how to overcome technical problems and how to interpret PAS results in meaningful ways. Applications of PAS in electronic and photonic materials, nuclear and irradiated materials, and engineering materials are discussed. Examples are given to guide the reader on how PAS can be combined with complementary methods to uncover the fundamentals of defect physics and reveal interesting new phenomena in condensed matter.

Abstract: This study is based on the density functional theory and employs the projected augmented wave method within the VASP program package. It investigates the variation of lattice constants in Fe₂P-type compound FeMnP_0.67Si_0.33 in the ferromagnetic (FM) and antiferromagnetic (AFM) states, with the presence of Mn and Fe vacancy defects and Mn and Fe anti-site defects. the defect formation enthalpy of compounds containing vacancy and substitution defects were calculated using the Wagner-Schottky point defect thermodynamic model. It also investigates the relationship between the equilibrium concentration of point defects and the Mn content in the compound, as well as the variation of defect equilibrium concentration with temperature T. The calculation results show that the presence of point defects in the compound affects the lattice constants. In the FM and AFM states, the formation enthalpies of Fe anti-site and Mn anti-site defects is lower than that of Fe vacancy and Mn vacancy defects. The concentration of point defects increases with increasing temperature. The calculated results provide valuable theoretical references for the experimental preparation, defect analysis, and mechanical properties improvement of the Fe₂P-type iron-manganese-based FeMnP_0.67Si_0.33 compound.

Abstract: Point defects in wide band gap semiconductors have recently shown outstanding potential for implementing room temperature quantum bits and single photon emitters. These atomic scale tools can be used in various quantum information processing, sensing, and imaging applications. Silicon vacancy related photoluminescence centers in 4H, 6H, and 15R-SiC are among the most studied quantum bits that possess a particular spin-3/2 ground and excited state. The microscopic structures of these defects have been recently identified as isolated negatively charged silicon vacancy defects at the symmetrically non-equivalent silicon sites in SiC. Relying on this identification, here we carry out high precision ab initio simulations on negatively charged silicon vacancies in 4H and 6H-SiC and calculate the most important magneto-optical data, such as the zero-phonon photoluminescence energies, the zero-field-splitting, and the hyperfine tensors for the nearest and farther nuclear spins.

Abstract: The development of bipolar 4H-SiC devices for high blocking voltages requires the growth of high carrier lifetime epitaxial layers with low Z_1/2 concentrations. This paper shows a comprehensive investigation of the influence of epitaxial growth parameters (C/Si ratio and growth temperature) on Z_1/2 concentration and minority carrier lifetime. On the basis of a discovered exponential correlation of Z_1/2 with the C/Si ratio and growth temperature, a competitive low Z_1/2 concentration of 1.9∙10¹² cm^-3 could be achieved by lowering the growth temperature and switching to higher C/Si ratio. Thermodynamic considerations by an Arrhenius approach reveal a dependency of the formation enthalpy of Z_1/2 on the thermal process and process conditions of the epitaxial growth. Furthermore, the correlation between Z_1/2 and the effective minority carrier lifetime confirms the occurrence of a necessary second recombination mechanism beside the common recombination at deep levels by Shockley-Read-Hall for low Z_1/2 concentration.

Abstract: The electrical characterization of high-purity semi-insulating 4H-SiC is carried out by means of current deep level transient spectroscopy (I-DLTS). Measurements are performed by employing either an electrical or optical pulse (below/above bandgap). The study performed on as-grown material, either annealed or oxidized, reveals the presence of six levels with ionization energies in the 0.4-1.3 eV range.

Abstract: The evaluation of the necessary duration of a molecular dynamics experiment for the calculation of the diffusion coefficient at migration of different point defects in Ni (vacancy, bivacancy, self-interstitial atom, hydrogen atom) is held in the present work. It is shown that at the temperature higher than 0.6 of melting point is usually enough the simulation during of 100 ps for this. When calculating of the diffusion coefficient of impurity in the metal crystal, for example, of hydrogen, the decrease of error of mean-square displacements of impurity atoms can be achieved by introducing of a large number of the impurities.

Abstract: In the work we propose a method for determining of the formation energy of bivacancy using molecular dynamics method. The key moment of the method for determining of the formation energy of bivacancy is the use of the value ζ, the minimum work that must be spent to remove one atom to infinity from the kink in the monatomic step on the surface of the crystal, calculated indirectly through the experimental data on the formation energy of the vacancy and the sublimation energy. The energy of migration of bivacancy in the work was determined from the temperature dependence of the diffusion coefficient when one bivacancy was introduced into the calculation block.

Abstract: Uranium silicides are envisaged as potential nuclear materials for the next generation. U₃Si is featured by the high actinide density and the better thermal conductivity relative to UO₂. To properly and safely utilize nuclear materials, it is crucial to understand their chemical and physical properties. First-principles in theory is mostly used to analyze the point defect structures for uranium silicides nuclear fuels. The lattice parameters of U₃Si and USi₂ are calculated and the stability of different types of point defects are predicted by their formation energies. The results show that silicon vacancies are more prone to be produced than uranium vacancies in β-USi₂ matrix. The most favorable sites of fission products are determined in this work as well. According to the current data, rare earth elements cerium and neodymium are found to be more stable than alkaline earth metals strontium and barium in a given nuclear matrix. It is also determined that in USi₂ crystal lattice fission products tend to be stabilized in uranium substitution sites, while they are likely to form precipitates from the U₃Si matrix. It is expected that this work may provide new insight into the mechanism for structural evolutions of silicide nuclear materials in a reactor as well as to provide valuable clues for fuel designers.

Abstract: Studies in the literature have shown how the different processing steps can have an impact on the electronic properties of SiC devices. In this contribution, we will review the importance of preserving the crystalline integrity of SiC epilayers through the major processing steps like etching, implantation and oxidation. It will be shown that the major cause for SiC device failures, e.g bipolar degradation and low field effect mobility, is the presence of carbon-related defects like the carbon vacancy (V_C) and carbon interstitials (C_i). At last, the different techniques devised to reduce the presence of these harmful defects will also be reviewed.