Kinetics Of Point Defects Research Articles

Influence of N2O oxidation of silicon on point defect injection kinetics in the high temperature regime

In this work we investigate the influence of N2O oxidation on the kinetics of point defects at high temperatures. The interstitials that are injected during the oxidation process are monitored by the growth of preexisting oxidation stacking faults. We show that at high temperatures (1050–1150 °C), the supersaturation of self-interstitials in the silicon substrate is enhanced when oxidation is performed in a N2O ambient compared to 100% dry oxidation. This behavior is attributed to the presence of nitrogen at the oxidizing interface. However, at lower temperatures this phenomenon is reversed and oxidation in N2O ambient leads to reduced supersaturation ratios.

Defects and material processing in compound semiconductors

This paper consists of three parts. In the first part, current understanding on intrinsic point-defect equilibria in GaAs is reviewed. Regarding defect equilibria in the bulk, the amphoteric native defect (AND) model is outlined to indicate the Ga vacancy equilibrium concentration. In the second part, the model is extended to include surface Fermi-level pinning in order to predict the profile of the equilibrium concentration of Ga vacancies in the sub-surface layers. The extension generalizes the formation kinetics of point defects and naturally derives a surface “bottle-neck effect” for point-defect formation: The surfaces do not always act as perfect sinks or sources for intrinsic point-defect formation through Schottky-type defect formation which has generally been assumed. Dislocations induce a bulk “bottle-neck effect” by which they do not always act as perfect sinks and sources. In the third part, diffusivity data of plasma-induced intrinsic point defects at low temperature are presented with high-temperature data of vacancies. They are of an acceptor-type and highly mobile even at room temperature. The point defects are suggested to be interstitials rather than vacancies.

Modelling point defect dynamics in the crystal growth of silicon

The quality of silicon single crystals grown by the Czochralski (CZ) and floating zone (FZ) methods depends on the distribution of microdefects formed by silicon vacancies and interstitials and by impurities, such as oxygen and carbon. This paper describes the first steps of an attempt to model the formation of these defects by combining atomistic-level simulation of the equilibrium, transport, and kinetics of point defects and impurities in silicon, with continuum modelling of defect transport and reaction. The continuum models are written in terms of classical equilibrium, transport and kinetic coefficients, which are estimated using atomistic simulations based on the Stillinger-Weber interatomic potential for describing the interactions of silicon atoms. Atomistic simulations are reported for the equilibrium and transport properties of interstitials and vacancies in pure silicon. Calculations predict that interstitials prefer to form 〈110〉 dumbbells in the diamond lattice and that these point defects become delocalized at elevated temperatures. A model is proposed for the recombination of vacancies and interstitials that leads to a high entropic energy barrier at high temperatures due to this delocalization. Calculations of continuum point defect distributions for a prototype, steady-state crystal growth system predict the transition between vacancy (D-defects) and interstitial (A-defects) dominated precipitation of microdefects as a function of temperature gradient, crystal pull rate and crystal radius. These predictions arein qualitative agreement with experiments for FZ-grown crystals.

Thermodynamics and kinetics of point defects in manganous sulphide

The defect equilibria and diffusion kinetics of point defects and manganese ions in manganese sulphide have been discussed with the background of available literature data. It has been shown that the behaviour of defects over the whole phase field of this compound can be satisfactorily described in terms of point defect thermodynamics. Over the major part of the homogeneity range, doubly ionized cation vacancies and electron holes are the dominating defects, manganous sulphide being a metal deficit p-type semiconductor (Mn1−yS). Near the Mn/MnS phase boundary, on the other hand, doubly ionized interstitial cations and quasi-free electrons prevail, the sulphide being thus a metal excess n-type semiconductor (Mn1+yS). The enthalpy and entropy of cation vacancy formation in Mn1−yS and those of interstitial cations in Mn1+yS, have been calculated. Both near and at the stoichiometric composition, the defect structure of manganous sulphide is more complex and strongly dependent on temperature. Below about 1100 K, intrinsic Frenkel electronic disorder dominates. In agreement with the defect model it has been shown that the self-diffusion of cations in Mn1−yS proceeds by a simple vacancy mechanism via doubly ionized cation vacancies, randomly distributed in the crystal lattice. The activation enthalpy and entropy of this process have been calculated. On the other hand, diffusion of manganese ions in Mn1+yS proceeds by an interstitial mechanism, in which the cation enters from its normal lattice site into a neighbouring interstitial position. In agreement with theoretical predictions, the activation enthalpy of this process has been found to be considerably higher than that of the vacancy diffusion. It has been demonstrated that the minimum rate of manganese self-diffusion at a given temperature corresponds very well to the stoichiometric composition of the sulphide, which is again in agreement with the defect model.

Convergence to the steady state for the reaction-diffusion kinetics of irradiation-produced defects

The kinetics of irradiation-produced point defects in solids are modelled by certain reaction-diffusion equations in one spatial dimension. For various boundary conditions the global asymptotic stability of the stationary solution is proven using the integrated version of a non-smooth Lyapunov function.

On the global asymptotic stability of a system of N generalized chemical rate equations

It is proved that a system of N generalized chemical rate equations, which for N = 2 describes the kinetics of irradiation-produced point defects, has a unique equilibrium point in the part of phase space where all dependent variables are positive. By finding an appropriate Lyapunov function, it is also shown that this equilibrium point is globally asymptotically stable, for all positive initial conditions of the system.

On the integrability of the generalized chemical rate equations for irradiation-produced point defects

The method of Painlevé property is applied to an N-dimensional generalization of a system of chemical rate equations describing the kinetics of irradiation-produced point defects. An algorithm is proposed for finding coefficients of the system for which the equations have the Painlevé property and are therefore expected to be completely integrable. This procedure is demonstrated here explicitly for the case N = 3 and some applications are given for the cases N = 2 and N = 4.

Kinetics of point defects in electron irradiated MgO

Abstract The kinetic behavior of point defects in MgO has been studied through the observation of the nucleation and growth processes of dislocation loops during electron irradiation in a high voltage electron microscope. Results have been obtained on dislocation loop formation and growth in MgO single crystals obtained from three sources during irradiation at temperatures from 25 to 1000°C. Circular and elongated dislocation loops with 1 2 〈110〉 Burgers vectors lying on {110} planes are formed in Norton MgO and ORNL and Tateho MgO, respectively. The loop nucleation stage is complete early in the irradiation and the density of loops reaches a saturation value CL. The diameter of loops D increases with irradiation time t. The dependence of CL and D on t and electron flux φ at various temperatures T is expressed as follows: C L ∝ t 0 φ −1 2 and D ∞ t 1 2 − 2 3 at T ≲ 600° C and D tφ −1 2 at T ≳ 600° C . Experimental results below ≈ 600°C are successfully analyzed using a theory based on a nucleation mechanism controlled by interstitial motion in which one or two pairs of Mg- and O-interstitials serve as stable nuclei for interstitial loops. The growth kinetics of loops above ~ 600°C are understood in terms of the steady state behavior of interstitials and vacancies with high mobilities, and are controlled by the vacancy species (Mg or O), the product of whose mobility and displacement rate has the lower value.

Analysis of the kinetics of point defects measured in internal friction under irradiation experiments

In this work the influence of the kinetics of migration of the stage III irradiation-created point defects on the peaking effect observed in internal friction measurements is analysed in the framework of a model recently proposed by Caro et al. (1982) for dislocation dynamics. The values obtained for the diffusion parameters are discussed in terms of two existing rate equation models for diffusion.

Electron microscope investigations on ion damage in platinum

Modern electron microscopes with lift- and tilt-stages allow small defect clusters in different samples to be investigated under nearly identical imaging conditions, especially with respect to magnification and excitation error. Taking advantage of these identical imaging conditions and applying statistical averages of may defects, it is possible to obtain very accurate mean sizes of defect clusters. Recent contrast calculations which consider both the depth positions and the actual sizes of the defects (l) make it possible to obtain the actual sizes of the observed defects from their images rather precisely. It is thus possible to detect very small changes in the mean cluster sizes as functions of different parameters, e.g., irradiation temperature Tirr at which the defects have been created, or their annealing treatment. Electron microscopy thus can provide data on the kinetics of point defects in addition to more conventional methods, e.g., resistivity-recovery and damage-rate measurements.This paper reports on electron microscopy investigations on the temperature dependence of ion-damage in platinum.

Thermal Equilibrium Kinetics of Interacting Point Defects

The local kinetics of an interacting defect species is treated on the assumption that local thermal equilibrium prevails, and a thermal equilibrium diffusion coefficient appropriate to any locality is derived in its general form. The annealing of an interacting defect species to sinks in the lattice is then shown to be identical with that of noninteracting defects having a diffusion coefficient ${D}_{\mathrm{eff}}=\frac{\ensuremath{\Sigma}\stackrel{}{n\ensuremath{\alpha}}n{{c}_{n\ensuremath{\alpha}}}^{0}{D}_{n\ensuremath{\alpha}}}{\ensuremath{\Sigma}\stackrel{}{n\ensuremath{\alpha}}n{{c}_{n\ensuremath{\alpha}}}^{0}},$ where ${{c}_{n\ensuremath{\alpha}}}^{0}$ is the concentration far from the sink of an $n\mathrm{th}$ order cluster of type $\ensuremath{\alpha}$, and ${D}_{n\ensuremath{\alpha}}$ is its diffusion coefficient. The importance of the particular case when ${{c}_{n\ensuremath{\alpha}}}^{0}$ achieves the thermal equilibrium value ${{c}_{n\ensuremath{\alpha}}}^{t}$, is noted, and the range of applicability of this diffusion coefficient is discussed.