Excitons and Biexcitons in Semiconductors

This chapter introduces the essential physics of excitons. In Sects. 1.1 and 1.2, and partially in Sect. 1.5, the individual properties of excitons are considered. The basis of the microscopic theory and the theoretical group classification of exciton states is given. The characteristic properties of excitons are discussed in terms of the relative electron–hole and translational motion. The spin structure and the longitudinal–transverse splitting of excitons due to long-range Coulomb interactions are considered in the framework of a simple two-band model for a semiconductor. The most impressive results are achieved in the physics of high-density excitons, a field that continues to develop rapidly (see Chap. 4). The main results in this domain are summarized in Sect. 1.3. The Lenard–Dyson theorem is an important basis for understanding the stability of the ground state of a system of particles interacting through Coulomb forces. In Sect. 1.5, we discuss the effect of impurities capturing one or two excitons. Examples include the capture of excitons by isoelectron traps, resulting in the formation of bound excitons or localized exciton molecules.