TABLE OF CONTENTS The objective of this chapter is to provide additional knowledge about defects and their effects on properties beyond that already given in previous chapters. Also, the section headings in this chapter will deviate from the formula used in the previous chapters. In this chapter the section headings are provided by the structural units rather than by properties. Hopefully, this new approach will provide new understanding of the relations between defects and properties.
Grain boundaries affect a myriad of electrical and other properties in semiconductors. In the following we shall consider first the structure of grain boundaries in tetrahedrally bonded semiconductors and the possible defects that these grain boundaries may encompass. Then we will consider those effects of grain boundaries and their associated defects on properties which have not already been discussed in the other chapters of this book.
To the best of this writer's knowledge the only theoretical studies on grain boundaries in silicon reported in the literature prior to 2004 involve tilt and twist boundaries only,47 except for one preliminary study of a random high angle boundary52 These theoretical studies47 of tilt grain boundaries in silicon suggest a multitude of modes of bonding all involving fourfold coordination. The simplest boundaries studied have a perfect <011> tilt axis and contain the tilt axis. The calculated energies of such tilt boundaries are shown in Figure 7.1. There are but two defects in such boundaries: Lomer dislocations and twin units. The ?9 boundary was...
