Interactions of electrons and photons in semiconductors form the basis of technologies such as optical communications, display, and optical memories. In this and the next chapter we will discuss how electrons in a semiconductor interact with light. To describe this interaction, light has to be treated as particles (i.e., photons). The problem is mathematically quite similar to the electron-phonon (lattice vibration) scattering problem discussed in Chapter 6. Electron-photon interactions are described via scattering theory through an absorption or emission of a photon. Both intraband and interband processes can occur as shown in Fig. 9.1. Intraband scattering in semiconductors is an important source of loss in lasers and can usually be described by a Drude-like model where a sinusoidal electric field interacts with electrons or holes. Monte Carlo methods or other transport models can account for it quite adequately. The interband scattering involving valence and conduction band states is, of course, most important for optical devices such as lasers and detectors. In addition to the band-to-band transitions, increasing interest has recently focussed on excitonic states especially in quantum well structures. The exciton-photon interaction in semiconductor structures contains important physics and is also of great technical interest for high speed modulation devices and optical switches. Excitonic effects will be discussed in the next chapter.
We will briefly review some important concepts in electromagnetic theory and then discuss the interactions between electrons and photons. We will focus on the special aspects of this interaction for semiconductor electrons, especially those relating to selection rules.