Material Properties Related to Point Disorder

Point Defects and Phase Diagrams. As will become more evident in subsequent parts of this chapter, substitutional impurities are one of the key types of point disorder. These defects correspond to foreign atoms that are taken into the lattice and which occupy sites normally reserved for the host atoms. For example, in the case of fee A1 some small fraction of the host lattice sites can be occupied by Cu 

Doping in Semiconductors. The electrical conductivity is one of the most diverse of material parameters. In passing from the best insulators to the best conductors (excluding the case of superconductivity), measured conductivities vary by more than 20 orders of magnitude, as illustrated in fig. 7.2. 

As was remarked as early as chap. 1, many of the properties of materials are not intrinsic in the sense that they are highly dependent upon the structure, purity and history of the material in question. The electrical conductivity is one of the most striking examples of this truth. Nowhere is this more evident than in considering the role of doping in semiconductors. This is hinted at in fig. 7.2 where it is seen that the conductivity of Si ranges over more than 6 orders of magnitude as the concentration of impurities is varied. In fig. 7.3 this effect is illustrated concretely with the variation in resistivity of Si as a function of the concentration of impurities. 

Though we will not imdertake any systematic analysis of the electronic implications of the presence of boron (or other dopants) in Si, it is evident that questions surrounding the energetics of impurities in Si are an important part of the whole picture of defects in semiconductors. One question of obvious significance is that 

Internal Friction. The application of a stress to a material containing point defects leads to measurable consequences that differ from those of an imaginary solid which is free of such defects. In particular, through the application of an alternating stress field, it is possible to induce microscopic rearrangements involving such 

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