Dislocations electrical activity

Key words Metal organic vapor phase epitaxy (MOVPE), dislocations, electrical activity of dislocations, transmission electron microscopy, electron holography... 

Some of the major questions that semiconductor characterization techniques aim to address are the concentration and mobility of carriers and their level of compensation, the chemical nature and local structure of electrically-active dopants and their energy separations from the VB or CB, the existence of polytypes, the overall crystalline quality or perfection, the existence of stacking faults or dislocations, and the effects of annealing upon activation of electrically-active dopants. For semiconductor alloys, that are extensively used to tailor optoelectronic properties such as the wavelength of light emission, the question of whether the solid-solutions are ideal or exhibit preferential clustering of component atoms is important. The next... 

The present study is focused on dislocations in ZnO epilayers grown by MOVPE. The distribution of edge, mixed and screw dislocations was analyzed for layers grown under different MOVPE conditions using TEM. Electron holography was applied to study the electrical activity of threading dislocations. 

A number of the well-known radiation-induced centers in silicon, which are known to involve broken bonds, are also neutralized by atomic hydrogen. For exanple, the A-center (oxygen+vacancy coitplex, -0.18 eV), and divacancy level (E -0.23 eV) may be passivated [65]. Point defects produced by the Q-switched ruby-laser-annealing of both n-type [66] and p-type [67] Si surfaces are neutralized to the melt depth of - 1 /mi by plasma exposures of just 10 minutes at 100°C. And there has been a lot of work on the passivation of the electrical activity associated with dislocations (and their attendant point defects) and grain boundaries [66-76], which is so helpful in making photovoltaic solar cells from polycrystalline materials. While these defects may involve broken bonds, it should be remembered that these... 

The driving forces necessary to induce macroscopic fluxes were introduced in Chapter 3 and their connection to microscopic random walks and activated processes was discussed in Chapter 7. However, for diffusion to occur, it is necessary that kinetic mechanisms be available to permit atomic transitions between adjacent locations. These mechanisms are material-dependent. In this chapter, diffusion mechanisms in metallic and ionic crystals are addressed. In crystals that are free of line and planar defects, diffusion mechanisms often involve a point defect, which may be charged in the case of ionic crystals and will interact with electric fields. Additional diffusion mechanisms that occur in crystals with dislocations, free surfaces, and grain boundaries are treated in Chapter 9. 

For instance, dislocations have been shown to play a key role in the accommodation process in YTZP, justifying the threshold stress in YTZP, in contrast with the hypothesis that this threshold stress is due to the electric field created by impurity segregation. However, dislocations are not systematically observed in YTZP furthermore it was shown that in yttria-stabilized tetragonal zirconia single crystals, the stress necessary to activate dislocations at 1400°C was over 400 MPa, one order of magnitude higher than the stresses used during superplastic deformation of YTZP at the same temperature. It will be necessary to conduct a systematic study of the microstructure of the monolithic ceramics such as YTZP before and after deformation and to correlate their relationship with the superplastic features. 

This study confirms our previous result [8] that even ultrashort shock experiments with laser and electric discharge guns are well suited to reproduce shock defects known to occur in naturally shocked minerals. For example, dislocation glide and twinning activated in the experimentally shocked specimens have also been detected in weakly shocked limestones from the Ries crater [50]. 

As in the electric discharge experiment, two sets of primary twins generally interpenetrate, which also induces a second generation of twins (Fig. 1.13a). Activated dislocations occur at a density varying between 1013 and 1014nT2. Strong interaction between dislocations is manifested in numerous triple junctions. 

Those sites of dislocations of edge and screw are beneficial to the catal3dic reactions. The other is that the electronic factors on those sites of crystal lattice irregularity enhance the high catal3dic activities, because the surface points correlated with the dislocations and defects can modify the electrical properties of solids. 

It is well known that dislocation etch pits on the surfaces of metals are produced in solutions of salts of other metals as a result of contact displacement reactions (53)(54). The size of pits formed by these solutions depends on the concentration of a salt and the time of etching. However, prolonged etching often leads to the precipitation of mono- or polycrystalline displaced metal at relatively more active sites where dissolution is faster than that at the rest of the surface. Subsequent etching can yield etch hillocks, as observed In the case of etching white tin in acidic solutions of CuSO. Whether etch hillocks or etch pits will be formed at dislocation sites Is determined by the exchange kinetics at the electric double layer and by the diffusion kinetics. 

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