Native Interstitials Research Articles

First-Principles Investigation of Native Interstitial Diffusion in Cr2O3

First-principles density functional theory investigation of native interstitials and the associated self-diffusion mechanisms in α-Cr2O3 reveals that interstitials are more mobile than vacancies of corresponding species. Cr interstitials occupy the unoccupied Cr sublattice sites that are octahedrally coordinated by 6 O atoms, and O interstitials form a dumbbell configuration orientated along the [221] direction (diagonal) of the corundum lattice. Calculations predict that neutral O interstitials are predominant in O-rich conditions and Cr interstitials in +2 and +1 charge states are the dominant interstitial defects in Cr-rich conditions. Similar to that of the vacancies, the charge transition levels of both O and Cr interstitials are located deep within the band gap. Transport calculations reveal a rich variety of interstitial diffusion mechanisms that are species-, charge-, and orientation-dependent. Cr interstitials diffuse preferably along the diagonal of corundum lattice in a two-step process via an ...

Localization and movement of native interstitials in chlorinated SrCl2:Fe crystals

The formation of the electron trapped Fe+(IV) centre, produced by X-ray irradiation at 80 K and further annealing at temperatures of up to 700 K in chlorinated SrCl2:Fe crystals, has been investigated by Electron Paramagnetic Resonance. Our studies report the transformation of the monoclinic Fe+(III) centre into the axial Fe+(IV) centre above 450 K. The formation of the Fe+(IV) centre is attributed to the presence and thermally activated movement of neighbouring interstitial chlorine and alkali impurity Na+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The electronic properties of native interstitials in ZnO

To investigate the role of interstitial geometry, we reported ab initio calculations of octahedrally and tetrahedrally native interstitials in ZnO, using the full-potential linear muffin-tin orbital method. The results show that both zinc interstitials could contribute to the native n-type conduction in ZnO, meanwhile, the zinc vacancy and octahedral oxygen interstitial may contribute to the p-type conduction in ZnO. We also suggest that the 31 and 61 meV donors found by temperature-dependent Hall experiment originate from tetrahedral- and octahedral zinc interstitials, respectively, based on their charge distribution. It is noticeable that tetrahedral interstitials cause stronger interaction between interstitials and its neighboring atoms than that of octahedral interstitials.

Pressure and Strain Effects on Diffusion

AbstractWe have investigated, via parameter-free calculations, the effects of hydrostatic and nonhydrostatic strains on the energetics of defect formation and self-diffusion in silicon. The three microscopic mechanisms, vacancy, interstitial, and concerted exchange, have very similar activation enthalpies at zero pressure but exhibit different behavior with hydrostatic pressure. Our results suggest that experiments performed at different pressures can determine the relative contributions of each of these mechanisms. The calculations also show that the neutral Si vacancy has a negative relaxation volume, with the nearest neighbors of the vacancy relaxing inwards, in contrast to the Si (111) surface. Large nonhydrostatic strains, which are present in e.g. Si/GexSi1-x pseudomorphic heterostractures, substantially reduce the formation energy of the tetrahedral interstitial, but do not affect the formation energy of the vacancy. These findings suggest that, aside from being another useful tool for the investigation of self-diffusion in Si, nonhydrostatic strain may significantly affect annealing and impurity diffusion in strained heterostructures. In particular, the interstitial-assisted impurity diffusion may proceed more rapidly in Si lattice-matched to GexSi1-x, but be slowed down in GexSi1-x lattice-matched to Si. The compressed GexSi1-x layers may thus act as diffusion barriers for impurities diffusing with help of native interstitials, such as B or P.

The generation of point defects in GaAs by electron-hole recombination at dislocations

The degradation of GaAs heterojunction lasers results in the formation of long dislocation dipoles which grow by a climb process involving point defect concentrations of the order of 1019 cm−3. The driving force for this climb process is not understood and it has been suggested that the material contains a supersaturation of native interstitials which condense on the dislocation during device operation. An alternative model proposed that the driving force is related to the energy released by electron-hole recombination on the dislocation which is partially dissipated by the dislocation emitting vacancies into the surrounding lattice.Gallium arsenide substrates containing greater than 2 × 1018 tellurium atoms cm−3 contain interstitial concentrations of the order of 1017 cm−3 which condense out to form small dislocation loops during an anneal at 880°C. The presence of these loops indicates that the annealed material does not contain excess interstitials in solution. This annealed material was optically pumped and examined by transmission electron microscopy. It was found that the loops developed into dipoles typical of degraded lasers. The number of point defects involved in this climb process increased with increasing pumping power and time. These results are discussed in terms of the two mechanisms listed above and it is concluded that the energy released by electron-hole recombination at the dislocation provides the driving force for the climb process.

Statistical Mechanics of Dilute Solid Solutions

An apparently quite general model for an essentially-ordered semiconductor compound containing impurity traces consists: (1) of atomic point defects randomly distributed over appropriate, equivalent sites and contributing to the internal energy of the crystal by terms linear in the concentration of each type of atomic point defect, and (2) an electronic energy band structure in which the concentration and type of ``impurity'' levels is determined by the concentration and type of atomic point defects. The assignment of donor or acceptor character to the native interstitials and vacancies is predicted in a specific case by analogy with the alkali halides. Otherwise the nature of the binding is irrelevant, provided the un-ionized impurity level associated with each substitutional atomic point defect bears the same charge as that on the substituted atom. From the appropriate quasi-grand partition function, one obtains the usual Fermi-Dirac distribution for electrons as well as distribution functions for the atomic point defects. In addition, one obtains expressions for the chemical potentials of the thermodynamic components. The latter are utilized in a discussion of those aspects of the M–N phase diagram pertinent to the semiconductor compound MN and in a discussion of amphoteric impurities.