Depth Profiles Of Defects Research Articles

Simulation of damage induced by ion implantation in Lithium Niobate

A simulation tool has been developed to engineer the damage formation in Lithium Niobate by ion irradiation with any atomic number and energy. Both nuclear and electronic processes were considered and, in particular, the dependence on the ion velocity of the electronic excitation damage efficiency has been taken into account. By using this tool it is possible both to draw damage nomograms, useful to qualitatively foresee the result of a given process, and to perform reliable simulations of the defect depth profiles, as demonstrated by the good agreement with the experimental data available in the literature.

Depth profiling of vacancy defects and their thermal stability in N-implanted Si: a positron annihilation study

Depth-resolved positron annihilation studies have been carried out on nitrogen-implanted Si to investigate defect evolution and thermal stability. Si(1 0 0) wafers have been implanted with 60 keV N+ ions to a fluence of 1 × 1014 and 1 × 1015 ions/cm2. From positron diffusion analysis of defect-sensitive S-parameter profiles, it is found that the higher dose sample undergoes a two-step annealing process consisting of annealing of deep level defects, followed by vacancy agglomeration near the surface at 873 K. For the low dose sample, however, nitrogen vacancy complexes are the only major defects remaining at 873 K. Annealing at 1073 K is sufficient to remove all kinds of open volume defects present in the samples.

Raman scattering in silicon disordered by gold ion implantation

AbstractSi (111) covered by a 250‐nm thick SiO2 surface layer has been disordered through implantation of 3.035 MeV gold ions within broad range of fluences from 1 × 1013 ions/cm2 to 1 × 1016 ions/cm2. Raman spectroscopy (514.5 nm laser) was applied for characterization of the silicon disordering. Variation of the Raman spectra of silicon after low‐fluence implantation (fluences lower than 5 × 1014 ions/cm2) in the vicinity of the transverse optical phonon (1TO) peak reflects the coexistence of bulk Si crystals (c‐Si) and Si nanocrystals (nc‐Si) in the implanted layer. Implantation with higher fluences yields only the stable 470 cm−1 1TO peak, corresponding to formation of amorphous phase (a‐Si), in this region of the spectra. Detailed analysis of the silicon disorder was performed through calculation of the transverse acoustical phonon (1TA) peak area. The fluence dependence of the peak area reveals qualitative correlation with the depth profile of structural defects in the modified Si layer evaluated from RBS (Rutherford backscattering) experiment and from SRIM (stopping and range of ions in matter) code simulation. This correlation suggests a decrease of the structural disorder in the modified layer region enriched by vacancies.

Sizing of 3-D Arbitrary Defects Using Magnetic Flux Leakage Measurements

In this paper, we propose a new procedure to estimate the shape of the opening and the depth profile of an arbitrary three-dimensional (3-D) defect from magnetic flux leakage (MFL) measurements. We first use the Canny edge detection algorithm to estimate the shape of the defect opening. Then we use an inversion procedure based on the space mapping (SM) methodology in order to approximate the defect depth profile efficiently. To demonstrate the accuracy of the proposed inversion technique, we reconstruct defects of arbitrary shapes from simulated MFL signals. The procedure is then tested with experimental data of two metal-loss defects. In both cases, the proposed approach shows good agreement between the actual and estimated defect parameters.

Hydrogen‐induced defects in Pd films

AbstractHydrogen absorbed in crystalline solids causes a lattice expansion and the formation of hydride phases. Contrary to free standing bulk samples, thin films are fixed at substrates, which prevent their in‐plane expansion. This makes hydrogen‐induced expansion of thin films highly anisotropic and leads to the formation of high stresses in hydrogen loaded thin films. As a consequence, lattice defects may be created in thin films loaded with hydrogen. This work reports about defects created by hydrogen loading in epitaxial Pd films deposited on Al2O3 substrates by cold cathode beam sputtering. Hydrogen‐induced defects are characterized by positron annihilation spectroscopy performed with variable energy slow positron beams. Extended studies of defect depth profile and its development with increasing concentration of hydrogen are performed by measurement of Doppler broadening of annihilation profile using a continuous positron beam. Selected states are investigated also by positron lifetime spectroscopy on an intense pulsed positron beam. Firstly, the microstructure of virgin films is characterized. Subsequently, the hydrogen concentration in the films is increased step‐by‐step by electrochemical charging. The development of the film microstructure and the evolution of defects are investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Implantation-caused open volume defects in Ge after flash lamp annealing (FLA) probed by slow positron implantation spectroscopy (SPIS)

B + and P + ions were implanted into Ge wafers covered with a pre-amorphised surface layer of 150 nm. After this, flash lamp annealing (FLA) in Ar atmosphere was used as post-implantation heat treatment. Radiation with Xenon flash lamps, having a spectrum in the visible range of light and a pulse length of 3 ms or 20 ms, allowed an ultra-short heating up of the near surface region. In this way, a modification of the structure of the as-implanted amorphous Ge layer was possible. Depth profiles of defects, especially those of the vacancy-type, were investigated by slow positron implantation spectroscopy (SPIS) before and after FLA. It was found that the remaining vacancy-type defect structure depends on the parameters of the process of heat treatment, and that these defects could not be completely removed by FLA. Results are compared with such from SRIM 2006 calculations (stopping and range of ions in matter) and Rutherford backscattering spectrometry (RBS).

Depth Profiling of Defects in He Implanted SiO2

Thin layer of SiO2 thermally grown on p-type Si was implanted with He ions at 30 keV with a dose of 5× 10 ions/cm. SiO2/Si samples were depth profiled by Doppler broadening positron annihilation spectroscopy to identify induced defects in the silicon oxide, at the interface and in the Si substrate. In one sample the silicon dioxide layer was removed by etching after implantation. It is shown that removing the silicon dioxide layer some more information about defects into the substrate can be found.

Depth profiling of defects in stainless steel using electric potential sensors and a non-contact AC potential drop method

A new technique is described a non-contact version of the well-known AC potential drop method. Electric potential sensor technology is capable of measuring, non-contact, the spatial electric potential associated with a sample via the displacement current, through capacitive coupling. This can be achieved due to the extremely high input impedance of the sensors, resulting in many cases in no loss of signal when compared with a contact voltage measurement. For laboratory samples, an AC current is passed through the sample and the spatial potential above the surface monitored as a function of position. For a full non-contact implementation this current would be induced inductively as in eddy current testing systems. Previous work on stainless steel using this new technique was able to detect 1 mm of material loss from the inside of a 24 mm-thick sample. The work described here extends this by applying multiple frequencies simultaneously to a sample and analysing the data for each frequency component separately. In this way, depth information about faults within a material may be obtained, due to the skin depth effect. This enables the location and characterisation of faults in three dimensions to be achieved while only performing a single scan.

Thick diamond layers angled by polishing to reveal defect and impurity depth profiles

Diamond layers were grown top a thickness of 25 to 35 μm either on type- Ib synthetic or type- IIa natural diamond substrates by using high or low microwave-power densities. To evaluate defects and impurities depth profiles, the samples were angled by polishing and characterized by cathodoluminescence. The first important finding is that boron, nitrogen and structural defects seem to be concentrated in a 7–10-μm-thick region near the substrate/layer interface, as evidenced by strong defect or impurity-related luminescences and a weak free-exciton peak. The diamond quality is thus much improved in the bulk or near the surface, especially when high microwave-power densities are used, due to the inhibition of unepitaxial crystals formation. The second important finding is that using type- IIa natural substrates, which contain extremely low levels of impurities, results in a strong decrease in the amount of boron and the intensity of the nitrogen-related peak both in the bulk and at the interface of the CVD layer. These results suggest that most impurities in our CVD layers could originate from the substrate itself.

Thermal stability of Co, Ni, Pt or Ru Schottky contacts on n-Si and defects introduced thereon during contacts fabrication using electron beam deposition

When using Schottky barrier diodes (SBDs) on silicon (Si) to study the thermal stability of radiation-induced defects, point defects injection into the silicon substrate can occur at temperatures where silicidation occurs. These injected point defects can react with the radiation-induced defects and may lead to an incorrect picture of annealing studies of these defects. In order to overcome this problem, we have annealed (1) ruthenium (Ru), cobalt (Co), nickel (Ni) and platinum (Pt) SBDs to form stable silicides on phosphorus (P) doped Si and (2) have measured the electrical characteristics of defects introduced during diodes fabrication by electron beam deposition (EBD), using conventional and (high resolution) Laplace (L-) deep level transient spectroscopy (DLTS). A primary electron trap at 0.48 eV below the conduction band was observed after EBD processing of the contacts. Isochronal annealing of the SBDs at 350 °C, annealed-in defects 0.05, 0.09, 0.18 and 0.28 eV below the conduction band. All the EBD-induced defects were removed after annealing at 600 °C. Primary defect depth profile versus annealing temperature results are also presented in this study.

Defects around self-organized InAs quantum dots measured by slow positron beam

Self-organized InAs quantum dots (QDs) have been fabricated by molecular beam epitaxy. The authors try to use a slow positron beam to detect defects in and around self-organized QDs, and point defects are observed in GaAs cap layer above QDs. For the self-organized InAs QDs without strain-reducing layer, it is free of defects. However, by introducing a strain-reducing layer, the density of point defects around larger sized InAs QDs increased. The above results suggest that low energy positron beam measurements may be a good approach to detect depth profiles of defects in QD materials.

Modification of new polymer materials based on aminostyrene by irradiation

The ultra-violet (UV) irradiation induced modification of the mechanical and optical properties of several polymer composites containing 4-aminostyrene and glycidyl methacrylate and their dependences on radiation dose, structure and ageing have been investigated. The nano- and microindentation techniques were used for determination of the mechanical parameters of as-grown and irradiated materials. The light-induced structural changes result in an increase of the hardness and elastic modulus of the polymer layers up to five and three times, respectively. It is also shown that the influence of polymer structure is significant. The conditions for improvement, degradation and stabilization of physical properties by UV irradiation were established. Load and depth sensing indentation has proved to be a powerful tool for an accurate estimation of mechanical properties of cross-linking polymer compositions. Variable-energy positron annihilation spectroscopy (slow-positron beam technique) was developed to measure defect depth profiles in the near-surface region. The increase of S-parameter with the increase of nano-hardness and elastic modulus has been determined for these materials.

Positron annihilation spectroscopy for the determination of thickness and defect profile in thin semiconductor layers

We present a method, based on positron annihilation spectroscopy, to obtain information on the defect depth profile of layers grown over high-quality substrates. We have applied the method to the case of $\mathrm{ZnO}$ layers grown on sapphire, but the method can be very easily generalized to other heterostructures (homostructures) where the positron mean diffusion length is small enough. Applying the method to the ratio of $W$ and $S$ parameters obtained from Doppler broadening measurements, $W∕S$ plots, it is possible to determine the thickness of the layer and the defect profile in the layer, when mainly one defect trapping positron is contributing to positron trapping at the measurement temperature. Indeed, the quality of such characterization is very important for potential technological applications of the layer.

Depth profiling of strain and defects in Si∕Si1−xGex∕Si heterostructures by micro-Raman imaging

We have reported depth and in-plane profiling of strain, Ge composition, and defects in strained-Si∕Si1−xGex∕Si heterostructures using micro-Raman imaging. Raman profiling in the depth direction was carried out with a depth resolution of ∼15nm using a small-angle beveled sample and ultraviolet (UV) excitation. Depth profiles of the Ge composition and Raman bandwidth clearly show that the defect density depends strongly on the Ge-grading rate in a compositionally graded Si1−xGex layer. The in-plane strain variation at a given depth in each layer has been evaluated. The in-plane strain variations in the Si1−xGex are closely related to clustering of misfit dislocations in the graded Si1−xGex layer. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain. The close correlation between the frequency and bandwidth is attributed to inhomogeneous strain fields associated with misfit dislocation clusters, which induce complete relaxation of strain in constant composition Si1−xGex layers.

Charge-state dependence of energy loss of MeV dimers inGaAs(100)

Carbon and oxygen dimers with charge states $1+$ and $3+$ were implanted into $\mathrm{GaAs}$ along the [100] direction at an energy of $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{atom}$. The defect depth profiles are extracted from Rutherford backscattering spectrometry and channeling. The depth profile of carbon is extracted from secondary ion mass spectrometry measurements. The defect density produced by dimer ions is larger than monomer ions. The depth profile of carbon in dimer implanted $\mathrm{GaAs}$ is deeper than that of monomer implanted $\mathrm{GaAs}$ showing negative molecular effect. The defect depth profile of oxygen dimer implanted $\mathrm{GaAs}$ is deeper for $3+$ than that for $1+$ charge state. This indicates that energy loss of ${\mathrm{O}}_{2}^{3+}$ is smaller than that of ${\mathrm{O}}_{2}^{+}$. It is attributed to charge asymmetry and a higher degree of alignment of ${\mathrm{O}}_{2}^{3+}$ along the [100] axis of $\mathrm{GaAs}$.

Defect depth scanning over the positron implantation profile in aluminum

We present an experimental setup which allows us to measure in a nondestructive way a defect depth profile in light metals and alloys. For this we employ the implantation profile of positrons emitted from the radioactive source (22Na) which is sensitive probe for open volume defects in crystalline lattice. We demonstrate the setup and the experimental technique using a pure aluminium sample whose surface was damaged after a blasting treatment. A well defined defect profile was detected which coincides well with that established using an alternative technique. The presented setup can be useful for detection of subsurface zones in tribological studies for example.

Subsurface Zone in Pure Magnesium Studied by Positron Lifetime Spectroscopy

This paper presents the results of investigation of a subsurface zone created during dry sliding in pure magnesium. Positronannihilation and microhardness techniques were used to detect the defect distribution below the worn surface. Near to the surfacethere was found a strong gradient of dislocations and defects associated with them, which were extended more than a hundred ofmicrometers. The decrease of microhardness at a depth less than 30 lm from a worn surface suggested that dynamic recovery tookplace in pure magnesium. The defect profiles were also studied for samples exposed to compression and blasting.KEY WORDS: subsurface zone, positron annihilation, defect depth profile, magnesium

EBIC and DLTS characterization of pure Si crystals

Possibilities of measurements of low defect concentration in Si by the electrical methods are discussed. The problems arising in such measurements are illustrated by measurements of iron concentration in Si. It is demonstrated that gold diffusion experiments can be used for revealing and study of some electrically inactive defects. Possibility of nondestructive reconstruction of defect depth profiles by DLTS and using the profile obtained for understanding the defect nature is illustrated by the results of hydrogen and hydrogen related defect investigations. EBIC investigations of dislocations are shown to be a rather sensitive method for revealing recombination defects.

Positron Lifetime Measurements of Subsurface Region in Aluminium Alloy and Aluminium Alloy Composite after Dry Sliding

This paper presents positron lifetime studies of the subsurface region of AK12 aluminium alloy and Al2O3-particle-reinforced AK12 aluminium alloy composite after sliding against steel in the pin-on-disc machine. The defect depth profile detected in the AK12 alloy extended up to 300 μm but for the composite AK12 the range of this profile was significantly shortened to less than ∼ 90 μm. The positron lifetime dependence on depth evidences a steep gradient of defect concentration near the surface. The subsurface zones have been also examined using scanning electron microscopy.

Characterization of metastable defects in hydrogen-implanted n-type silicon

Using deep level transient spectroscopy (DLTS) measurements with zero-bias and reverse-bias cooling, we have observed new metastable defects (EM1, EM2 and EM3) in n-type silicon by hydrogen implantation at temperature as low as 88 K. We have investigated the trap parameters of these metastable defects and their concentration depth profiles. Hydrogen ion implantation was performed with energies of 80 keV, 90 keV, and 100 keV to a dose of 2 x 10 10 cm -2 . The silicon substrate temperature was kept at as low as 88 K during hydrogen implantation and then was raised naturally to room temperature. From analysis of Arrhenius plots, the energy levels of EM1, EM2 and EM3 are obtained to be Ec-0.29 eV, Ec-0.41 eV and Ec-0.55 eV, respectively. The depth profiles of metastable defects in 90-key samples have a peak in the concentration around the depth of 0.68 μm, which is shallow compared with the projected range of 90 keV hydrogen. The peak position becomes deeper as the energy of ion implantation increases. This indicates that the production of metastable defects is caused by ion implantation. Additionally, comparison with helium-implanted samples suggests that implanted hydrogen is included in these metastable defects.