Semiconductors are important materials. Because of their unique electronic properties, they are the materials of choice for modern electronic devices. Silicon, in particular, has become the most important material for the electronics industry. Besides their unique properties for electronics applications, semiconductors also have many other important properties that are very useful for photonic device applications. In earlier chapters, we have already seen that III–V semiconductors are useful materials for opticalwaveguides and electro-optic devices. Many semiconductors are also used for acousto-optic devices and nonlinear optical devices. In such applications, which are based solely on the dielectric properties of semiconductors, semiconductors are nothing but another group of dielectric optical materials. Nevertheless, semiconductors do have many optoelectronic properties that are not shared by other dielectric materials. These optoelectronic properties make semiconductors once again, beyond their unique position in the electronics industry, the key materials for many important optoelectronic devices, such as light-emitting diodes, semiconductor lasers, and photodetectors. These devices are covered in the following two chapters. In this chapter, we review the basic properties of semiconductors that are relevant to their optoelectronic device applications.

Semiconductors

In Chapter 10, optical transitions between discrete atomic or molecular energy levels are considered, though the atoms or molecules may be embedded in a host solid-state material as dopants. In a semiconductor, however, the allowed states of the electrons of its constituent atoms form continuous energy bands rather than discrete levels. The optical processes associated with such electrons are a strong function of the characteristics of the energy bands.