Agglomeration Of Defects Research Articles

Bound vacancy interstitial pairs in irradiated silicon

Frenkel defects are produced by MeV electron irradiation of Si with an introduction rate of ≈ 1 cm −1 and we show that defect concentrations as high as 10 19 cm −3 can be frozen in at 4 K. From X-ray diffraction we deduce that a large fraction of the defects is stabilized in the form of close Frenkel pairs and that the long range displacement fields of interstitial atoms and vacancies cancel nearly exactly. Additional larger defect agglomerates are observed at higher irradiation doses. The defect patterns observed after 4 K irradiations are compared to those of room temperature irradiations and the relative importance of ionization induced and thermally activated migration is discussed. Results for Cz-Si are compared to those obtained for FZ-Si and the thermal annealing is discussed with special emphasis to the reduction of the effective defect mobility by trapping reactions.

Structural disorder in SiGe films grown epitaxially on Si by ion beam sputter deposition

SiGe/Si heterostructures grown by ion beam sputter deposition were characterized by high-resolution X-ray diffraction and transmission electron microscopy. Agglomerates of point defects, formed under ion bombardment during growth, were observed in electron microscopy images. These specific defects resulted in structural disorder which could be described in terms of local fluctuations of interplanar distances. The averaged magnitudes of the fluctuations were derived from X-ray diffraction spectra using a novel simulation procedure based on the direct summation of scattered waves in imperfect heterostructures. This approach allowed us to characterize quantitatively the degree of the structural disorder, and to follow defect transformations as a function of growth and annealing temperatures.

Microstructure of Ultra High Dose Self Implanted Silicon

ABSTRACTThis study has investigated the microstructure of ultra high dose (∼ 1018 cm−2) self implantation into Si. Implants have been carried out into both (100) Si and pre-amorphised Si as a function of implant temperature between liquid nitrogen temperature and 350°C. Results show that high dose implantation into completely amorphous Si (a-Si) produces layers which regrow quite well during subsequent solid phase epitaxy. In contrast, implantation into crystalline Si (c-Si) or part amorphous/part crystalline Si can lead to rich and varied microstructures at elevated temperatures, even extending to porous-like structures in some cases. Strong dynamic annealing and agglomeration of points defects in c-Si is thought to be responsible for such behaviour.

Point Defects Migration and Agglomeration in Si at Room Temperature: The Role of Surface and Impurity Content

ABSTRACTOur recent work on the room temperature migration and trapping phenomena of self-interstitials and vacancies in crystalline Si is reviewed. Spreading resistance profiling and deep level transient spectroscopy measurements were used to monitor the interaction of ion beam generated defects with dopant atoms, intrinsic impurities (i.e. O and C), pre-existing defect marker layers and sample surface. We have found that both interstitials and vacancies undergo fast long range migration which is interrupted by trapping at impurities and by recombination at defects or at the surface. Effective defect migration lengths as large as 5 μm at room temperature have been observed in highly pure, defect free epitaxial Si samples. A lower limit of 1×10−10 cm2/sec for the room temperature diffusivity of self-interstitials has been determined. Furthermore, by monitoring the migration and interaction processes of point defects injected through a mask, we have established that surface acts as an effective sink for the migrating Si self interstitials.

Identification of Microdefects in Multicrystalline Silicon

ABSTRACTMicrodefects in multicrystalline silicon grown by directional solidification have been investigated by transmission electron microscopy. Their density (=106 cm−2) correlates with the density of shallow etch pits observed after chemomechanical polishing and selective etching. Different types of microdefects (size 10 – 100 nm) could be identified: i) spherical precipitates most likely amorphous silicon dioxide, ii) small plates lying on {111} planes and iii) groups of closely spaced stacking faults having the character of dipoles. It is argued that these defects are the result of agglomeration process of intrinsic point defects and impurities, where oxygen and carbon are the main candidates. A qualitative comparison to the point defects agglomeration observed in Cz material will be given.

Defects in Ion-Implanted 3C–SiC Probed by a Monoenergetic Positron Beam

Defects introduced by 200-keV N2+- or Al+-implantation into 3C–SiC were probed by a monoenergetic positron beam. Depth profiles of the defects were determined from measurements of Doppler broadening profiles of the annihilation radiation as a function of incident positron energy. For ion implanted specimens at high substrate temperature (≥800° C), the major species of defects was identified to be vacancy clusters. The depth profile of vacancy-type defects was found to be shifted towards the surface of the specimen by implantation at high temperatures. Upon furnace annealing after the implantation, an agglomeration of vacancy-type defects was observed, and interstitial clusters were introduced below the vacancy-rich region.

Novel effects of weak magnetic fields on post-implantation damage in semiconductors and superconducting ceramics

Novel experimentally verifiable and theoretically explained effects of weak static magnetic fields (WSMFs) acting during ion implantation of semiconductors and superconducting ceramics (SCC) at 300 K, moderate ion energies (e.g. 200–400 keV) and low dosage (e.g. 10 11–10 13 m −2) on the post-implantation radiation damage (PIRD) and material parameters are discussed. The WSMF of strength of H ≈ 1 kOe reduces, as previously reported, the PIRD in Hg 08Cd 02Te and InSb by factors of 2 and 1.54, respectively, and can increase the PIRD and change material parameters in SCCs. The WSMF effects on the radiation damage is a generic consequence of the kinetic electron-related theory of atomic rate processes in solids which shows that local electron transitions (LETs) in the nanometer vicinity of hopping atoms (defects) influence exponentially defect formation and migration rates. The magnetic field changing the LET number affects exponentially the rates of formation, migration and agglomeration of point defects and thus change the radiation damage.

Effects of hydrogen on structural relaxation and defect evolution in amorphous silicon

Hydrogenation effects on the structural relaxation and defect evolution in amorphous silicon (a-Si) prepared by ion implantation and evaporation have been investigated using Raman scattering spectroscopy and positron lifetime measurements. Bond angle deviation Δθ in nonhydrogenated a-Si was significantly reduced due to 300 °C annealing in atomic hydrogen atmosphere. This indicates that the reduction in Δθ of hydrogenated amorphous silicon (a-Si:H) is not only due to relaxation during the deposition process of a-Si:H films as proposed by Jackson et al. [Philos. Mag. B 64, 611 (1991)] but also due to posthydrogenation of nonhydrogenated a-Si. It was also found that agglomeration of vacancy-type defects in evaporated a-Si during 450 °C annealing is enhanced after posthydrogenation, while no remarkable enhancement can be seen in a-Si prepared by ion implantation.

SIMS study on redistribution of implanted impurities in InSb and InAs during post-implantation annealing

The concentration profiles of beryllium and magnesium implanted in InSb and InAs at an energy of 200 keV and a dose of 10 15 cm −2 of beryllium and a dose of 5 × 10 14cm −2 of magnesium were investigated by SIMS analysis, in samples as-implanted and annealed at 300°C–800°C for InAs or at 300°C–450°C for InSb. It is found that in InSb samples the magnesium profiles did not broaden up to 350°C, but beryllium profiles did not even change up to 450°C. In InAs modification of the beryllium profiles in comparison with InSb occurred at relatively low temperatures about 400°C and an increase of annealing temperature from 400°C to 700°C resulted in a severe distortion of the original profile. At temperatures above 700°C a gettering layer in the region near R p resulted from the agglomeration of radiation defects. This layer acted as a sink of diffused beryllium.

Dynamic model of the wall structure in persistent slip bands of fatigued metals II. The wall spacing and the temperature dependence of the yield stress in saturation

It is suggested that the dislocation walls of persistent slip bands (PSBs) are elements with intrinsic features such as a characteristic width and a characteristic yield stress. The model predicts that the properties of the walls show only a weak temperature dependence. The observed remarkable temperature dependence of the yield stress of PSBs (plateau stress) is attributed to the mechanisms by which new walls are nucleated in the channels. The model takes into account the populations of the edge dislocations, of the screw dislocations and of the point defect agglomerates. The constitutents of the three populations have characteristic lifetimes. It is concluded that the short-living screw dislocations adapt themselves to the behaviour of the longer-living edge dislocations and point defect agglomerates which accordingly determine the features of a PSB.

Significant differences in defect accumulation behaviour between fcc and bcc crystals under cascade damage conditions

Various aspects of irradiation-induced damage production and accumulation in fcc and bcc metals and alloys are examined. Results on the evolution of defect morphology in individual cascades, the global evolution of planar (clusters/loops) and three-dimensional defect agglomerates (voids) and the temperature dependence of defect accumulation in the form of loops and voids in fcc and bcc metals are compiled and compared. The comparison demonstrates that the damage accumulation in the form of clusters/loops and voids and their dependence on irradiation temperature are dramatically different in fcc and bcc metals. These differences may arise because of significant differences in the number of surviving defects (in cascades) and intracascade clustering of vacancies and self-interstitial atoms (SIAs) that get established already during the thermal spike phase of cascades. The implications of these differences are discussed. It is suggested that theoretical treatments of the damage accumulation in fcc and bcc metals must explicitly include the details of intracascade clustering of vacancies and SIAs, for example, the ratio of clustered to non-clustered vacancies and SIAs.

Positron Annihilation Studies of the Ni-H Systems Containing Thermally Induced Crystal Lattice Defects

In the previous papers [1, 2] the results of the investigations of positron annihilation quanta in plastically deformed and electron beam irradiated nickel samples saturated with hydrogen were reported. These results regarding the interaction of hydrogen with vacancies, voids and dislocations are rather surprising. Nickel belongs to the group of metals in which an intense trapping of positrons in crystal lattice defects is observed. This suggests that hydrogen should be also intensively trapped in these defects. However, no effect of hydrogen on positron annihilation, which could confirm this suggestion, has been observed. Our previous experiments do not confirm the suggestion regarding the hydrogen trapping at crystal lattice defects. The results indicate that introduction of hydrogen into nickel samples containing defects, created by plastic deformation or electron bombardment, causes the changes in the annihilation parameters suggesting an increase in both the concentration and dimensions of crystal lattice defects. It has been suggested that the main reason for the observed changes in the positron annihilation parameters is the agglomeration of defects in the presence of hydrogen atoms in the sample. Later measurements of the positron lifetime in plastically deformed samples have shown an increase in the intensity of the long living component in the samples containing hydrogen. The low value (0.05 eV) of the hydrogen-vacancy and

Impurity ion implantation into silicon single crystals: efficiency and radiation damage

The ion implantation method is analysed from the point of view of its efficiency as a technique for doping silicon with donor and acceptor impurities, for synthesising silicon-based compounds and for producing gettering layers and optoelectronic structures. The introduction, agglomeration, and annealing of radiation-produced defects in ion-implanted silicon are considered. The role of interstitial defects in radiation-related defect formation is estimated. Mechanisms of athermal migration of silicon atoms in the silicon lattice are analysed.

Phase stability of nanostructured materials under heavy ion irradiation

Nanocgstalline Pd and ZrO 2 samples of theoretical density were irradiated with 4 MeV Kr +ions with doses up to 6.10 17 ion/cm 2. The irradiated samples were characterized by XRD, RBS, and TEM. Nanocrystalline ZrO 2 shows no amorphisation and defect agglomeration after irradiation with Kr + ions up to a dose of 2·10 17 ions/cm 2. A phase transformation from the monoclinic phase to a tetragonal phase could be observed. The comparison of irradiated n-Pd with a conventional polycrystalline Pd sample shows a reduced defect agglomeration in n-Pd. For n-Pd samples grain growth after irradiation experiments could be observed.

Electron Microscopy Investigation on the Effect of Plastic Deformation in the Alloying of the Immiscible System Cu-Fe

The first steps of the solid state reaction between Cu and Fe induced by plastic deformation at low temperature have been studied by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). Despite the positive enthalpy of mixing, plastic deformation induces interdiffusion in this system as evidenced by XRD and DSC analysis. TEM observations of samples prepared in different ways show the presence of some Fe into the Cu matrix, a relatively low density of dislocations, a large concentration of small agglomerates of point defects and a well-defined grain shape, suggesting that some dynamic recrystallization occurs during deformation. Considering the low processing temperature we advance the hypothesis that the excess concentration of point defects induced by the high strain rate plastic deformation can provide the necessary atomic mobility. Moreover the role played by these defects on the thermodynamic driving force of the alloying process is considered.

Investigation of radiation damage by X-ray diffraction

X-ray diffraction methods allow the investigation of point defects and small defect agglomerates or precipitates, i.e. defect sizes ranging from the atomic level up to large dislocation loops that are well above the visibility limit of the transmission electron microscope. The discussion includes measurements of the change of the lattice parameter and differential dilatometry as well as the diffuse scattering. Especially the diffuse scattering at small q-values, i.e. close to Bragg reflections (Huang diffuse scattering) and at small angles (small angle X-ray scattering), allows a rather straightforward interpretation and is discussed in some detail. The power and the limitations of the methods are illustrated through examples of defects in metals and semiconductors. Finally the application of the anomalous scattering and the investigation of the extended X-ray absorption fine structure are discussed, as synchrotron radiation makes these techniques generally available.

Rate theory investigation of influence of cascade cluster formation and solute trapping on point defect agglomeration and extended defect evolution

Using a composite model of point defect behavior and microstructural evolution, the influence of cascade vacancy cluster formation and vacancy trapping at solute atoms on the point defect fluxes, point defect clustering and extended defect development was investigated. The point defect model calculates the concentrations of isolated and trapped point defects, and of simple or complex clusters. The extended defect model consists of individual rate theory models describing the evolution of cavities, Frank loops and network dislocations. Cascade vacancy clusters were observed to become the dominant sink for point defects in the early stages of irradiation at low to intermediate temperature. Therefore, the sink strength of the vacancy clusters largely determines the point defect flux and agglomeration rates. The calculations also showed that solute traps affect the irradiated microstructure to a large extent for certain combinations of trap concentration and trapping energy. Both the trap concentration and trapping energy have a non-monotonic effect on vacancy clustering though they do not change the interstitial flux significantly.

Helium impurity interactions in vanadium and niobium

Thermal helium desorption spectrometry (THDS) has been employed to study the nucleation and growth of helium defect agglomerates in niobium and vanadium. An important difference from other body-centered-cubic metals was the temperature at which helium was released from monovacancy type defects. In Mo and W the release takes place at 0.40 T m ( T m = melting temperature) but in V and Nb at 0.25 T m . This and other observations led to the conclusion that in nearly all interactions of helium with radiation-induced defects, impurities, mainly oxygen, are involved. Impurity levels of 20–30 appm are sufficient to completely suppress the type of helium behaviour that was found in Mo and W. Oxygen decorates the helium-vacancy complexes and makes the helium desorption temperature lower, but stabilizes the small defect complexes up to a temperature of about 700 K; beyond this temperature, nucleation of defect clusters is considerably reduced. Oxygen decoration has been observed to reduce the sink strength of the defects for helium trapping.

Al-O interactions in ion-implanted crystalline silicon

The formation and dissolution of Si-O-Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.

Reduction of post-implantation damage in semiconductors by weak magnetic fields

The experimental evidence of a reduction in the post-implantation damage by a factor of 2 and 1.5 in, respectively, Hg0.8Cd0.2Te and InSb caused by magnetic fields of H=0.7 kOe and 2 kOe at T=300 K is reported. This effect follows from the kinetic theory of atomic rate processes in solids linking them with the local electron transport in the submicrometre vicinity of the atoms, overcoming energy barriers. The magnetic field, which decreases the local electron transport, reduces exponentially rates of formation, migration and agglomeration of point defects and this decreases the post-implantation damage.