Intrinsic Defects in Semiconductors

In all previous consideration of crystal structure and crystal growth, for simplicity it has been assumed that the silicon crystal lattice is entirely free of defects. Of course, in reality, this cannot be true since at any temperature greater than absolute zero, no crystal of finite size can be absolutely perfect. Indeed, there are a number of different types of defects that can exist within the crystal lattice of any pure material. In general, such intrinsic lattice defects can be broadly classified in terms of dimensionality, viz., point, line, plane, and spatial or volume defects. Moreover, any foreign species present within the crystal lattice may obviously also be regarded as a kind of defect. As a matter of semantic terminology, such impurities are to be regarded as extrinsic lattice defects; however, as will become evident subsequently, these may actually initiate the appearance of intrinsic defects. In any case, it is useful to limit discussion (at least temporarily) to the various types of intrinsic defects, i.e., defects that do not require the presence of foreign atoms.