A rich variety of optical centers with high energy local vibrational modes has been found in electron-irradiated 4H-SiC in both the as-irradiated and annealed states. These energies have been measured and the annealing dependence of the optical centers has been investigated by low-temperature... (Read more)

Understanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first-principles molecular dynamics, we perform a systematic study of the nonequilibrium processes of radiation damage in... (Read more)

Positron lifetime spectroscopy was used to study native vacancy defects in semi-insulating silicon carbide. The material is shown to contain (i) vacancy clusters consisting of four to five missing atoms and (ii) Si-vacancy-related negatively charged defects. The total open volume bound to the... (Read more)

We find, using a local density approximation +Hubbard U method, that oxygen vacancies tend to cluster in a linear way in SrTiO₃, a prototypical perovskite oxide, accompanied by strong electron localization at the 3d state of the nearby Ti transition metal ion. The vacancy... (Read more)

Based on ab initio density-functional energetics for saturated (n=2m+2) fluorine-vacancy clusters F_nV_m for m up to 4, the authors set up a model showing that (a) fluorine-vacancy (F–V) aggregates in Si can form in any... (Read more)

Despite the observation by a number of groups of a strong luminescence sensitization effect of erbium ions by excitation exchange from silicon nanoclusters, there is considerable experimental evidence that the fraction of Er ions excited by Si-nc is actually very low for much of the material... (Read more)

The Ga vacancy mediated microstructure evolution of (Ga,Mn)As during growth and postgrowth annealing is studied using a multiscale approach. The migration barriers for the Ga vacancies and substitutional Mn together with their interactions are calculated using first principles, and temporal... (Read more)

The presence of vacancy clusters in carbon nanotubes has been assumed to explain the formation of carbon peapods and the difference between the experimentally measured and theoretical fracture strength of nanotubes. We use atomistic simulations at various levels of theory to study the... (Read more)

The dynamics of multivacancy defects in a graphene layer is investigated by tight-binding molecular dynamics simulations and by first principles calculation. The simulations show that four single vacancies in the graphene layer first coalesce into two double vacancies, each consisting of a... (Read more)

The annealing behavior of defects observed in electron paramagnetic resonance (EPR) and photoluminescence (PL) is discussed. We consider the divacancy (the P6/P7 EPR centers) and a previously unreported EPR center that we suggest is a V_C-V_Si-V_C... (Read more)

Diffusion and clustering of lattice vacancies in silicon as a function of temperature, concentration, and interaction range are investigated by kinetic lattice Monte Carlo simulations. It is found that higher temperatures lead to larger clusters with shorter lifetimes on average, which grow by... (Read more)

High resolution photoluminescence spectroscopy on heavily doped GaAs:N reveals the existence of excitons bound to a nitrogen cluster. The observed transitions are exceedingly sharp, similar to those observed for excitons bound to nitrogen pairs in high quality GaAs with the narrowest transition... (Read more)

A model of arsenic clustering in silicon is proposed and analyzed. The main feature of the proposed model is the assumption that negatively charged arsenic complexes play a dominant role in the clustering process. To confirm this assumption, electron density and concentration of impurity atoms... (Read more)

First-principles calculations carried out in 3C- and 4H-SiC show that small metastable carbon clusters can be created in irradiated SiC. The metastable carbon clusters possess occupation levels in the p-type as well as in the n-type 4H-SiC. Depending on the... (Read more)

Spin-polarized density functional calculations are carried out on Er and Er-oxygen defects in crystalline Si. We find that the interstitial site is favored but the diffusion barrier of Er_i is only 1.9 eV, and inevitably Er_i forms complexes with impurities and... (Read more)

Electron spin resonance (ESR) was used to study neutron-induced defects in silicon as functions of anneal temperature T_an. For T_an below 200 °C, the ESR response is dominated by the Si-P3 and Si-P6 spectra, as observed before. At T_an=200 ... (Read more)

We show direct evidence, obtained by positron annihilation spectroscopy, for the complexing of fluorine with vacancies in silicon. Both float zone and Czochralski silicon wafers were implanted with 30 keV fluorine ions to a fluence of 2×10¹⁴ ions/cm², and studied in the... (Read more)

Process-induced defects are a serious issue for modern sub-micron Si LSIs. To characterize such defects, two different techniques are useful: electrically detected magnetic resonance (EDMR) and transmission electron microscope (TEM), which can detect small (point) and extended defects, respectively. We applied EDMR and TEM to the issue of defect-induced leakage currents in dynamic-random-access memory (DRAM) cells. For our DRAM samples (a 0.25- μm-rule series), although TEM showed no extended defects, EDMR successfully detected two types of point defects: V₂+O x (Si divacancy-oxygen complexes) and larger Si vacancies (at least larger than V₆). We confirmed that these defects are the source of DRAM leakage currents. The observed defects were formed by ion implantation processes, but were more thermally stable than those in bulk Si crystals. The origins of this enhanced stability are attributed to the presence of oxygen atoms and a strong mechanical strain in LSIs. To clarify the origin of the complicated strain in LSI structures, we can directly measure the local-strain distribution in DRAM samples by means of convergent-beam electron diffraction (CBED) using TEM, which provides us with a valuable hint for understanding the formation mechanism of process-induced defects. (Read more)

Combining electron paramagnetic resonance measurements with ab initio calculations, we identify the V_CC_Si(Si_CC_Si) complex as a second annealing product of the silicon vacancy via an analysis of resolved carbon hyperfine interactions and of... (Read more)

The electronic, structural, and vibrational properties of small carbon interstitial and antisite clusters are investigated by ab initio methods in 3C- and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of carbon interstitials, e.g.,... (Read more)

We present ab initio calculations for internal interfaces in Si and SiC. Density-functional calculations within the local-density approximation and the pseudopotential-plane-wave approach are performed to understand the effect of such two-dimensional defects on the electronic properties. We... (Read more)

The annealing kinetics of mobile intrinsic defects in cubic SiC is investigated by an ab initio method based on density-functional theory. The interstitial-vacancy recombination, the diffusion of vacancies, and interstitials to defect sinks (e.g., surfaces or dislocations) as well as the... (Read more)

The photoluminescence center D_II is a persistent intrinsic defect which is common in all SiC polytypes. Its fingerprints are the characteristic phonon replicas in luminescence spectra. We perform ab initio calculations of vibrational spectra for various defect complexes and... (Read more)

Using positron annihilation measurements we observed the formation of thermal vacancies in highly As and P doped Si. The vacancies start to form at temperatures as low as 650 K and are mainly undecorated at high temperatures. Upon cooling the vacancies form stable vacancy-impurity complexes such as... (Read more)

mplanted fluorine is observed to behave unusually in silicon, manifesting apparent uphill diffusion and reducing diffusion and enhancing activation of boron. In order to investigate fluorine behavior, we calculate the energy of fluorine defect structures in the framework of density functional theory. In addition to identifying the ground-state configuration and diffusion migration barrier of a single fluorine atom in silicon, a set of energetically favorable fluorine defect structures were found (F_nV_m). The decoration of vacancies and dangling silicon bonds by fluorine suggests that fluorine accumulates in vacancy-rich regions, which explains the fluorine redistribution behavior reported experimentally. (Read more)

Using the self-consistent-charge density-functional-based tight-binding (SCC-DFTB) method, we have investigated the migration of vacancies at high temperatures, taking into account the entropy contribution to the Gibbs free energy. We have found that the energy barrier for sublattice migration of... (Read more)

Ab initio supercell calculations have been carried out to investigate clusters of carbon interstitials in 3C- and 4H-SiC. Based on the calculated formation energies, the complex formation of carbon interstitials or their aggregation to carbon antisites is energetically favored... (Read more)

We propose a mechanism for the annealing of vacancy-related defects in SiC, based on ab initio total energy calculations. Our mechanism is based on the formation and migration of carbon and nitrogen split interstitials resulting in C_Si(N_C)_n or... (Read more)

The effect of vacancies on the behavior of F in crystalline Si has been elucidated experimentally for the first time. With positron annihilation spectroscopy and secondary ion mass spectroscopy, we find that F retards recombination between vacancies (V) and interstitials (I) because V and I trap F to form complexes. F diffuses in the V-rich region via a vacancy mechanism with an activation energy of 2.12±0.08 eV. After a long annealing time at 700ºC, F precipitates have been observed by cross-section transmission electron microscopy which are developed from the V-type defects around the implantation range and the I-type defects at the end of range. (Read more)

The depth distributions of oxygen-related defects in separation-by-implanted oxygen wafers were determined from measurements of Doppler broadening spectra of the annihilation radiation. Vacany–oxygen complexes were introduced by implanting 180-keV oxygen at (2–6)×10¹⁷ ... (Read more)

First-principles computational methods are employed to investigate the structural, vibrational, optical and electronic properties of the self-interstitial aggregate, I₄ in silicon. We find the defect to be electrically active and identify it with the B3 EPR centre. We... (Read more)

Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor... (Read more)

Mn_i4⁰ clusters were investigated by electron paramagnetic resonance in silicon specimens with initial doping concentrations between 1.5?10¹⁵?P cm^-3 and 5?10¹⁶?B cm^-3. In n-type samples and in intrinsic samples, we obtained the EPR... (Read more)

Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in ¹⁶O, ¹⁸O, and mixed isotopic samples are consistent with a model... (Read more)

Formation of intrinsic and impurity defect complexes in hydrogenated monocrystalline silicon is studied. Hydrogen was incorporated into samples by different ways: either by proton implantation at 80 and 300 K, or by annealing at 1250°C for 30–60 min in a sealed quartz ampoule containing... (Read more)

Three centers that involve gold or platinum and hydrogen have been observed in n-type hydrogenated silicon by electron paramagnetic resonance. The first two centers, labeled Si-NL63 and Si-NL64, were detected in the gold-doped samples revealing hyperfine interaction with two gold atoms for the... (Read more)

Electron paramagnetic resonance has been used to study the influence of thermal treatments on defect evolution in helium-implanted Czochralski single-crystal silicon. It is shown that the thermal treatment induces helium migration and capturing by vacancy clusters that transform into pressurized... (Read more)

Infrared (IR) and electron paramagnetic resonance (EPR) studies of quenching-dependent hydrogen-related double donor (HDD) formed in proton-implanted n-Si and p-Si upon annealing above 300°C were carried out. IR data taken at liquid He and N2 reveal that quenching-dependent IR absorption lines... (Read more)

New (S=1) EPR spectrum (labeled Si-AA17) is observed in irradiated high-purity hydrogen-contained silicon after annealing at ≥200°C. The AA17 defect has D3d symmetry with g=2.0028, g=2.0106; A(29Si)=175.0 MHz, A=89.0 MHz; and D=±33.6 MHz, D=±16.8 MHz. It is paramagnetic in a... (Read more)

n- and p-type float-zone silicon containing 10¹⁸-cm^-3 tin were irradiated with 2 MeV electrons to a dose of 10¹⁸ cm^-2 and subsequently examined by electron paramagnetic resonance (EPR). The p-type material yields only the well-known Si-G29 signal due to... (Read more)

Manganese centers were investigated in silicon specimens with initial doping concentrations between 1.5?10¹⁵ P cm^-3 and 6?10¹⁵ B cm^-3. All known Mn centers could be observed but the cluster Mn_i3Mn_i was missing in highly-boron-doped... (Read more)

N-type silicon doped with gold and lithium was investigated by Electron Paramagnetic Resonance (EPR) and Deep Level Transient Spectroscopy (DLTS), using two sets of samples with different defect concentrations of both gold and lithium. Photoluminescence (PL) on both sets of samples allowed to... (Read more)

Using deep-level transient spectroscopy, we studied defect energy levels and their annealing behavior in nitrogen-doped 6H-SiC epitaxial layers irradiated with 2-MeV electrons and implanted with 300-KeV deuterium or hydrogen at room temperature. Five levels located at E_c-0.34,... (Read more)

2-MeV electron irradiation of Si at elevated temperature creates a dominant deep level at the energy E_c-0.36 eV in addition to the oxygen vacancies. This level, which is less significant in room-temperature-irradiated Si, is found to be an efficient recombination center in the present... (Read more)

Numerical tests of possible models for the oxygen dependence of the divacancy introduction rate in silicon electron irradiated at room temperature were performed on a computer. Only the model in which oxygen traps Si self-interstitials can reproduce all the experimental data. Our modeling results... (Read more)

Magnetic properties of the dislocation dangling bond (DDB) spin system in silicon crystals are investigated by means of the EPR technique at T = (1.3 to 150) K. Experimental results are obtained which enable one to develop a one-dimensional model of the spin system according to which the DDB chains... (Read more)