Mechanism Of Defect Creation Research Articles

Defect creation in diamond by hydrogen plasma treatment at room temperature

The defect creation mechanism of diamond by hydrogen plasma treatment at room temperature was investigated. Electron spin resonance (ESR) observation revealed that hydrogen plasma treatment at room temperature gave rise to a highly defective structure. In contrast, very few defects were created in silicon. The difference of the defect creation mechanism between diamond and Si was discussed on the basis of the existence of sp 2 hybridization in diamond network.

Depth distribution of carrier lifetime in 65 MeV oxygen ion irradiated silicon wafers

CZ-grown, n-doped crystalline Si(111) of resistivity 60Ωcm and 140Ωcm were irradiated with 65MeV energy oxygen ions, in the fluence range of 2×1010–1014ions/cm2. The depth and spatial profile of excess minority carrier recombination time τ (lifetime) was measured using photoconductive decay (PCD) method. Lifetime measurements were carried out before the stopping range of impinging ions. Results show a monotonous decrease in lifetime with fluence, which is attributed to defect creation mechanism by electronic energy loss based on the thermal spike model. Also, surface modification is expected with a small loss in crystalline quality. This surface is considered to be a multi-crystalline surface with large grain boundaries that act as trapping sites for excess holes in n-Si(111). Annealing of the irradiated samples showed a near complete recovery at 750°C for a period of 1h.

UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3–5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom) 0 -[AlO 4 ] + that is formed after the trapping of an electron and a hole by Li + (or Na + ) and AlO 4 .

Mechanisms of monovacancy annihilation and type-A defect creation on Si(001)?2$times;1

Based on first principles quantum mechanics (DFT/GGA with pseudopotentials) calculations, we propose a new mechanism for monovacancy annihilation and single missing dimer creation. Our study shows that an isolated monovacancy can exist fairly stable, rather than liberating the remaining atom of the `defect' dimer readily. The liberation barrier is calculated to be 1.3 eV. However, the monovacancy can diffuse rapidly along a dimer row by overcoming a barrier of 0.3 eV, leading to vacancy–vacancy pairing at elevated temperatures. These results suggest that the vacancy–vacancy pairing may play a major role in creating a single missing-dimer vacancy (which is ≈1.8 eV more stable than two isolated monovacancies). We also present the pathways and barriers of (i) the remaining atom hopping between the buckled-up and down site of the `defect' dimer and (ii) the vacancy diffusion into the subsurface layer.

UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3–5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom) 0-[AlO 4] + that is formed after the trapping of an electron and a hole by Li + (or Na +) and AlO 4.

Mechanisms of monovacancy annihilation and type-A defect creation on Si(0 0 1)–2 × 1

Based on first principles quantum mechanics (DFT/GGA with pseudopotentials) calculations, we propose a new mechanism for monovacancy annihilation and single missing dimer creation. Our study shows that an isolated monovacancy can exist fairly stable, rather than liberating the remaining atom of the `defect' dimer readily. The liberation barrier is calculated to be 1.3 eV. However, the monovacancy can diffuse rapidly along a dimer row by overcoming a barrier of 0.3 eV, leading to vacancy–vacancy pairing at elevated temperatures. These results suggest that the vacancy–vacancy pairing may play a major role in creating a single missing-dimer vacancy (which is ≈1.8 eV more stable than two isolated monovacancies). We also present the pathways and barriers of (i) the remaining atom hopping between the buckled-up and down site of the `defect' dimer and (ii) the vacancy diffusion into the subsurface layer.

Variable range hopping in hydrogenated amorphous silicon

We study the effect of high-temperature annealing on the conductivity temperature dependence of a-Si:H films. Two types of films were studied: uniform and nanolayered prepared by cyclic repetition of CVD and hydrogen plasma treatment. It is shown that for annealing temperatures above 450 °C, the low-temperature conductivity obeys the law ln σ = const − (T0/T)n, where the exponent is n ≅ 1/4 for uniform and n ≅ 1/3 for layered films indicating two-dimensional conduction for layered films. It is argued that the measurements of the conductivity temperature dependence can provide information about spacial distribution of defects produced by HTA and about the defect creation mechanism. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Light induced defects in sputtered amorphous silicon thin films

We have investigated the influence of light soaking on the electrical and optical properties of sputtered amorphous silicon thin films. The obtained results have shown that sputtered a-Si:H films, as well as glow discharged material are sensitive to prolonged light exposure. The most important induced states appear during the first 2 h of exposure. From the dark conductivity variation, we inferred that light induced defects are relatively low in hydrogen-rich films. We suggest that the mechanism of defect creation is performed through SiSi weak bonds breaking and that is stabilized by hydrogen involvement.

Determination of the defect creation mechanism in the mono-silicated fluoroapatite. Disorder modeling under repository conditions

Amorphization resulting from α-decay events can strongly reduce the chemical durability of nuclear waste matrices. The creation rate of defects produced by α recoils in mono-silicated fluoroapatite was determined using a transmission electron microscope (TEM) on line with an ion implanter and compared to previous results obtained in fully phosphated fluoroapatite. In both materials, the defect creation is controlled at room temperature, by the amorphization process directly in the cascade. Furthermore, it has been shown previously that in mono-silicated fluoroapatite, the disorder recovery proceeds mainly via α-annealing. Taking into account our already published data and new results on the defect creation in the mono-silicated fluoroapatite, we have modeled the amorphization level evolution versus time under repository conditions. The main conclusion is the following: thanks to α-annealing, mono-silicated fluoroapatite loaded with 244Cm, will maintain a disorder at a level low enough to prevent the total amorphization of the host lattice during the long-term disposal.

UV induced afterglow of KCl:Eu,KBr:Eu and NaCl:Eu at low temperature

We propose a model for the production of defects by non-ionising radiation in impurity-doped alkali halides based on the formation of impurity-trapped excitons by excitation of the impurity, instead of ionisation of the impurity as has been proposed before. The dissociation of the trapped excitons into F Z and H centres in our model is similar to the case of the formation of F and H centres induced by ionising radiation in pure alkali halides. To gather information about the mechanism of defect creation by non-ionising radiation, we investigate the afterglow (AG) emission induced by UV light at low temperature (20 K) in three different alkali halides: KCl, KBr and NaCl doped with Eu impurity. We conclude that the AG emission can be split into two components; one of them has a fast decay and the other one remains for several minutes, decaying according to t −1/2. This second component has a close relation with the thermoluminescence emission. We show that the decay of the second component can be explained within the framework of our model if we assume that the H centres migrate along lines. We suggest that these lines are dislocation lines.

Determination of the defect creation mechanism in fluoroapatite

Most of strategies to immobilize actinides are concerned with their incorporation in dedicated solid matrices for a long disposal-time. Chemical durability of these matrices is a major problem. Radiation damages due to α-decay events can strongly reduced it. The defect creation mechanism has been determined in fluoroapatite using a transmission electron microscope (TEM) on line with an ion implanter. At room temperature, the defect creation is controlled by amorphization directly in the cascade. From this result and published data on the defect annealing in this material, the disorder evolution as a function of time has been established. An application concerning the incorporation of 244 Cm is considered.

Damage induced in semiconductors by swift heavy ion irradiation

The behaviour of semiconductors under swift heavy ion irradiation is different from that of metals or insulators: no spectacular effect induced by the inelastic energy loss has been reported in these materials. We present here a review of irradiation effects in the usual semiconductors (silicon, germanium and gallium arsenide). The damage is investigated by means of electrical measurements. The usual mechanisms of point defect creation can account for the experimental results. Besides, some results obtained on the wide gap semiconductor silicon carbide are reported. Concerning the irradiation effects induced by heavy ions in particle detectors, based on silicon substrate, we show that the deterioration of the detector performances can be explained from the knowledge of the substrate properties which are strongly perturbed after high doses of irradiation. Finally, some future ways of investigation are proposed. The silicon substrate is a good example to compare the irradiation effects with different particles such as electrons, neutrons and heavy ions. It is then necessary to use parameters which account for the local energy deposition, in order to describe the damage in the material

Observation of edge dislocations in helical smectic liquid crystals

We report the observation of elementary edge dislocations in smectic liquid crystals possessing helical structure. The dislocations were observed in the entire temperature range of helical phases, including ferroelectric, ferrielectric and antiferroelectric phases. The mechanism for visualizing the dislocations is based on the phenomenon of selective reflection of circularly polarised light. The performed observations of dislocations deliver not only information on the mechanisms of defect creation in various chiral smectic phases, but also on the structure and properties of the investigated smectics, often inaccessible using standard methods.

Effect of surface on defect creation by self-ion bombardment of Si(001)

We have studied defect formation and defect distributions in silicon under low-energy (25\char21{}800 eV) self-bombardment of the $2\ifmmode\times\else\texttimes\fi{}1$ terminated Si(001) surface. We applied the classical molecular dynamics technique and collected statistically significant averages to be able to detect defect production trends in the energy dependence. The number of defects created in implantations was found to be a superlinear function of energy at low energies $(l400\mathrm{eV})$ and larger than the defect production in the bulk up to about 1 keV. We have also examined the depth dependence of close-to-surface damage and explored the energy and time dependence of the defect creation mechanisms and the sensitivity of the results to the choice of the model potential.

New Tight-Binding Method for Simulation of Defect Configurations, Creation and Diffusion Mechanisms in Solids: Application to Silicon

ABSTRACTThis paper presents the self-consistent tight-binding method of new generation which, unlike other tight-binding methods, allows one to calculate structural energies of multiatomic systems (molecules, clusters, defects in solids) and their spectroscopic energies in the framework of the same computational scheme and with comparable accuracy. Reliability of the method is illustrated considering defect state problems in crystalline and amorphous silicon (electronenhanced- atomic diffusion, metastable defect creation, defects with effective-negative correlation energies, etc.) and comparing obtained results with ab initio calculations and experimental data.

New Tight-Binding Method for Simulation of Defect Configurations, Creation and Diffusion Mechanisms in Solids: Application to Silicon

ABSTRACTThis paper presents the self-consistent tight-binding method of new generation which, unlike other tight-binding methods, allows one to calculate structural energies of multiatomic systems (molecules, clusters, defects in solids) and their spectroscopic energies in the framework of the same computational scheme and with comparable accuracy. Reliability of the method is illustrated considering defect state problems in crystalline and amorphous silicon (electron-enhanced-atomic diffusion, metastable defect creation, defects with effective-negative correlation energies, etc.) and comparing obtained results with ab initio calculations and experimental data.

Creation of metastable defects in a-Si:H by keV-electron irradiation at different temperatures

The creation of metastable defects in a-Si:H films by 20 keV-electron irradiation at different degradation temperatures, T deg, is investigated. At low degradation temperature ( T deg = −170°C) no significant difference in the defect creation kinetics compared to that at room temperature is observed. This result indicates that the defect creation mechanism is not thermally activated. At higher degradation temperatures ( T deg = 50−100°C) the defect creation kinetics is strongly dependent on temperature, T deg, and electron intensity, I el, due to an increasing influence of thermal annealing during degradation. To explain these effects quantitatively an expression for the defect creation kinetics is derived based on a model assuming different kinds of defects with different annealing behaviour. Moreover, the resulting fit parameters give further information for the understanding of the multi-valued relation between photoconductivity, σ ph, and defect density, N D, observed for different degradation states.

VUV spectroscopy study of lattice defect creation in rare gas solids

The lattice defect creation stimulated by exciton self-trapping into molecular type states (M-STE) in solid Xe is studied by a luminescence VUV spectroscopy method. A model of the “excited state” mechanism of lattice defect creation is developed. The main model parameters — the time of stable defect creation and the activation energy needed — are estimated. The feature associated with the desorbing dimers or/and dimers on the sample surface is found.

Mechanism of defect creation and light induced changes in compensated α-Si: H(B, Li) and α-Si: H(B, P) films

Metastable increase of dark conductivity with light soaking in compensated α-Si: H(B, Li) is reported for the first time. Similarity in the behavior of α-Si: H(B, Li) and α-Si: H(B, P) suggests similar mechanism for light induced Fermi level shift (Δ E F ) in both the cases. The kinetics of defect formation, annealing and stretch exponential decay of Δ E F infer a process involving light induced structural changes. A model has been proposed by which capture of holes at bistable charge trapping sites by deactivation of boron causes metastable increase of conductivity.

Efficiency of defects generation due to irradiation in silica

The efficiency of generation by irradiation of E′-centers in pure silica glass has been estimated analytically. The ionization of the oxygen nonbonding orbital was considered as a main mechanism of defect creation, allowing us to interpret the known experimental dose dependence of the concentration of the E′-centers produced by X-radiation.