Annihilation defects

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

Second, the energy of emission activation is close to the energy of activation of adsorption of oxygen by silver - 146 kj/mol [49]. This implies that emission of O-atoms occurs due to energy of defect annihilation in the surface-adjacent layers of catalyst due to adsorption of oxygen. From the stand-point of such assumption it is obvious that depletion of emission is linked with sloroing down of the oxygen absorption rate (as shown, for instance, in Fig. 6.12). 

Fig. 3.2. Two principal mechanisms of defect recombination in solids, (a) Complementary defect annihilation, r is the clear-cut (black sphere) radius, (b) distant tunnelling recombination due to overlap of wave functions of defects. Two principal kinds of hole centres - H and Vk...

The high temporal resolution of SFM imaging uncovered elementary dynamic processes of structural rearrangements. We observed short-term interfacial undulations [111], fast repetitive transitions between distinct defect configurations [112], their spatio-temporal correlations on a length scale of several microdomains [112], and unexpected defect annihilation pathways via formation of temporal excited states [51, 111]. 

The absorption band observed in all the MgO thin film samples at 5 eV ( 248 nm) corresponds to the presence of overlapping bands in the lattice due to F and F+ centers. Other observed bands that are less intensive at 5.7 eV ( 217 nm) can be due to the anionic vacancies (Kunsetsov and Yaek 1976). The absorption band that occurred at 3.42 eV ( 363 nm) can be assigned to the pairs of F centers in nearest neighbor sites in anionic sublattice along (110) direction (Kunsetsov and Yaek 1976). The broad absorption peak at 2.3 eV ( 540 nm) is due to the presence of V type centers in the cationic sublattice (Sender and Sibley 1972). The optical absorption band associated with metallic precipitate is observed at 560 nm, which is proportional to the number of hydrogen atoms in the metallic phase that dcCTcases with annealing. Further, the optical measurements indicate that V type defects annihilate completely at 450°C, while the bands due to F and F+ centers are annihilated partially at that temperature. This result was previously reported by Van Veen et al. (1999) that most of the F centers disappeared on annealing even below 450 C. 

We have here defect annihilation and a decrease in electrical conductivity as a result. 

Electronic transitions during bond breaking and during recombination/defect annihilation... 

Cross slip is a conservative mechanism that occurs under stress with the help of thermal activation. Climb reqnires point defect annihilations at the dislocation cores and can also be stress-assisted, bnt to a lesser extent. This indicates that cross shp can be operative at lower temperatures than climb, and points at the core structure of perfect screw dislocations as an important factor determining the stabUity of perfect shuffle dislocations. 

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