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 s
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Excitons and Biexcitons in Semiconductors
This chapter briefly deals with information on the physics of excitons. In Sects. 1.1 and 1.2, and partially in Sect. 1.5, the individual properties of the excitons are considered. The exciton states are classified on the basis of microscopic theory and group theory. The characteristic properties of the exciton influenced by the division of its movements, the relative movement of the electron–hole and the translational motion of the center of gravity of the electron–hole pair, as well as the spin structure and longitudinal–transverse splitting of the exciton by Coulomb far action are considered in the framework of a simple two-band model for a semiconductor. The most impressive successes have been achieved in the physics of high-density excitons, and this field continues to develop intensively (Chap. 4). The main results in this domain are briefly reflected in Sect. 1.3. We note that the Lenard–Dyson theorem is significant in understanding the stability of the ground energy state of a system with an arbitrary number of charged particles interacting according to Coulomb’s law. In Sect. 1.5 the role of impurities and their capture of one or two excitons is discussed. In particular, we note the capture of excitons by isoelectron traps with the formation of a bound exciton or a localized exciton molecule.
1.1 The Electronic Structure of Excitons The concept of excitons as specific excited states of crystals was first introduced in 1931 by Frenkel [80] in regard to molecular crystals. In the framework of the theory of excitons the processes of the absorption of light by intrinsic (without impurities) crystals without the accompaniment of photoconductivity and the mechanism of transformation of light into heat can be easily explained. The representations of excitons were further developed by Wannier [81] and Mott [82], and it was shown that the presence of excitons is a characteristic feature of the spectrum of elementary excitations of any nonmetallic crystal. Some 30–35 years after the basic work of Frenkel, the theory of excitons turned into a developed topic in solid state physics. I. Geru, D. Suter, Resonance Effects of Excitons and Electrons, Lecture Notes in Physics 869, DOI 10.1007/978-3-642-35807-4_1, © Springer-Verlag Berlin Heidelberg 2013
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1 Excitons and Biexcitons in Semiconductors
General monographs on the theory of excitons [83–87], and later books [88, 89] and other works were published. In a rather detailed form they set forth the achievements of that period, which could be called “the period of all-round investigation of individual exciton properties.” The first clear confirmation of Frenkel’s work [80] on the existence of excitons in crystals was determined experimentally in the work of Gross and coauthors [90] in 1952 and in Hayashi’s and Katsuki’s work [91] on the rich discrete structure of the long-wave edge of the absorption spectrum of the Cu2 O crystal. The concrete structure of excitons is different for different types of crystals and, accordin
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