Self-interstitials migration

The picture of self-interstitials in Si developed by Seeger and Frank (21) is consistent with observations indicating self-interstitial migration at low and high temperatures. 

Nastar M., Bulatov V. V. and Yip S., Saddle-Point Configurations for Self-Interstitial Migration in Silicon, Phys. Rev. B53, 13 521 (1996). 

However, most impurities and defects are Jalm-Teller unstable at high-symmetry sites or/and react covalently with the host crystal much more strongly than interstitial copper. The latter is obviously the case for substitutional impurities, but also for interstitials such as O (which sits at a relaxed, puckered bond-centred site in Si), H (which bridges a host atom-host atom bond in many semiconductors) or the self-interstitial (which often fonns more exotic stmctures such as the split-(l lO) configuration). Such point defects migrate by breaking and re-fonning bonds with their host, and phonons play an important role in such processes. 

Figure 8.6 Diffusiomil migration of a [100] split-dumbbell self-interstitial in an f.e.c.

Diffusion of Self-Interstitial Imperfections by the Interstitialcy Mechanism in the F.C.C. Structure. For f.c.c. copper, self-interstitials have the (100) split-dumbbell configuration shown in Fig. 8.5d and migrate by the interstitialcy mechanism illustrated in Fig. 8.6. The jumping is uncorrelated,8 (f = 1), and a/ /2 is the nearest-neighbor distance, so... 

Self-Diffusion by the Interstitialcy Mechanism. If their formation energy is not too large, the equilibrium population of self-interstitials may be large enough to contribute to the self-diffusivity. In this case, the self-diffusivity is similar to that for self-diffusion via the vacancy mechanism (Eq. 8.19) with the vacancy formation and migration energies replaced by corresponding self-interstitial quantities. The... 

Electron paramagnetic resonance measurements only identify vacancies or vacancy complexes in Si irradiated by electrons. The absence of Si self-interstitials has been ascribed to rapid athermal migration even at 2 K (13). 

Calculations of total energy show that self-interstitials form and migrate in Si with a total activation energy roughly the same as that of self-diffiision (25). 

The current majority opinion is that both types of point defects are important. Thermal equilibrium concentrations of point defects at the melting point are orders of magnitude lower in Si than in metals. Therefore, a direct determination of their nature by Simmons-Balluffi-type experiments (26) has not been possible. The accuracy of calculated enthalpies of formation and migration is within 1 eV, and the calculations do not help in distinguishing between the dominance of vacancies or interstitials in diffusion. The interpretation of low-temperature experiments on the migration of irradiation-induced point defects is complicated by the occurrence of radiation-induced migration of self-interstitials (27, 28). 

The 2.2 eV in equation 57 may represent the migration enthalpy of the phosphorus-self-interstitial pair (56) with the excess self-interstitials produced by damage annealing. 

Molecular reorientations at Bjerrum fault sites are responsible for the dielectric properties of ice. A second type of fault (proton jumps from one molecule to a neighbor) accounts for the electrical conductivity of ice, but cannot account for the high dielectric constant of ice. Further discussion of such ice faults is provided by Franks (1973), Franks and Reid (1973), Onsager and Runnels (1969), and Geil et al. (2005), who note that interstitial migration is a likely self-diffusion mechanism. 

At 1100°C, however, predominantly stacking faults are formed close to the surface and in the bulk /5,6/ (fig.5,6). Their length depends on oxidation time and atmosphere. Si self-interstitials formed in supersaturation at the oxidation front are absorbed by the stacking faults close to the wafer surface and do not migrate into the bulk of the wafer, while the stacking faults deep in the bulk grow due to incorporation of the interstitials emitted from... 

In-diffusion profiles of S were determined by means of secondary ion mass spectroscopy. In order to evaluate the shapes of the profiles, a set of coupled reaction-diffusion equations was solved numerically. From the simulated non-equilibrium profiles of in-diffusing S, which migrated via the kick-out mechanism, both the diffusion coefficient and the equilibrium concentration of As self-interstitials were determined simultaneously. The S diffiisivity at 950 to llOOC could be described by ... 

It was suggested that bulk Ag migration occurred via interstitial octahedral sites. The large misfit due to Ag atoms was related to the low activation energy of Ag as compared with that of the self-interstitial. 

The diffusion coefficient for a given ion in a crystal is determined, as we have seen, by the atomistic properties of the ion in the structural sites where the vacancy (or interstitial) participating in the migration process is created (see eq. 4.71). The units of diffusion (and/or self-diffusion ) are usually cm sec . Pick s first law relates the diffusion of a given ion A (Jf) to the concentration gradient along a given direction X ... 

Migration of atoms that occupy substitutional sites may occur through a range of mechanisms involving either vacancy- or interstitial-type defects. In f.c.c., b.c.c., and hexagonal close-packed (h.c.p.) metals, self-diffusion occurs predominantly by the vacancy mechanism [4, 5]. However, in some cases self-diffusion by the... 

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