Polycrystalline silicon dislocations

Inhomogeneous stress distributions that arise at the grain boundaries in polycrystalline silicon wafers were detected by fan-shaped dislocation clusters close to the grain boundaries. The dislocation clusters are formed during the solidification process and relieve stresses produced in the system. 

In general, dislocations are undesirable in crystals. Mechanically, they can lead to weakness that can cause fracture. Electrically, they interfere with conduction of electrons and reduce reliability, reproducibility, and efficiency in semiconductor devices. For example, one of the challenges of photocell manufacture is to raise the efficiency of cells made of polycrystalline silicon to levels that are reached by single crystals. 

Fig. 2.2. Schematic set-up of a top-seeded FZ apparatus. A float zone of the polycrystalline silicon supply rod is locally melted by the RF field of the coil located outside of the quartz tube. In this particular set-up, at the beginning of the process, the diameter of the single crystal is reduced to a few mm to prevent dislocations to propagate in the monocrystalline part continuing the monocrystalline seed [44]...

In this paper, we have given a summary of some of the aspects of the work done in our laboratory on hydrogen passivation in polycrystalline silicon ribbon. We have shown that the dominant defects being passivated are dislocations, that many of the dislocation-related defects can be passivated quite readily using a Kaufman ion source, and that passivation can proceed to depths > 200 pm in some cases with diffusivities down dislocation arrays > 10- cm /sec. Several examples have been chosen to demonstrate the enormous utility of the EBIC technique in studying passivation. 

Polycrystalline-alumina-based fibres can at present not compete with silicon-carbide-ba.sed fibres when low creep rates are required. Fibres with higher resistance to creep by dislocation motion could be provided by oxides with high melting point and complex crystal structure, a tendency to order over long distances and the maintenance of this order to high fractions of the melting temperatures (Kelly, 1996). Experimental development of monocrystalline fibres by Czochralski-derived techniques from chrysoberyl... 

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... 

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